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Nahime, Bacus de Oliveira [UNESP]. "Estabilização da fase perovskita e propriedades estruturais de filmes finos relaxores do sistema PLZT." Universidade Estadual Paulista (UNESP), 2016. http://hdl.handle.net/11449/138275.
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Programa de Capacitação dos Servidores do Instituto Federal de Educação, Ciência e Tecnologia Goiano
Filmes finos de Pb0,91La0,09(Zr0,65Ti0,35)O3 (PLZT) foram preparados sobre substratos Pt/TiO2/SiO2/Si(100), usando um método químico baseado no processo Pechini, com objetivo de estudar a supressão da fase pirocloro e a estabilização da fase perovskita. Pós de PLZT preparados por reação do estado sólido foram utilizados como principal fonte de íons Pb2+, La2+, Zr4+ e Ti4+ pela dissolução em solução ácida. A obtenção de resinas poliméricas estáveis com diferentes excessos de chumbo foi possível preparando-se separadamente as resinas de PLZT e PbO seguido de posterior mistura e homogeneização à temperatura ambiente.
Pb0,91La0,09(Zr0,65Ti0,35)O3 (PLZT) thin films were prepared on Pt/TiO2/SiO2/Si(100) substrates by using a chemical method based on Pechini process to study the pyrochlore phase suppression and to stabilizing the perovskite phase. PLZT powders prepared by solid state reaction were used as source of Pb2+, La2+, Zr4+ and Ti4+ ions by its dissolution in acid solution.
Programa de Capacitação dos Servidores do Instituto Federal de Educação, Ciência e Tecnologia Goiano, aprovado pela Resolução nº 028/2010 de 23/11/2010
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Nahime, Bacus de Oliveira. "Estabilização da fase perovskita e propriedades estruturais de filmes finos relaxores do sistema PLZT /." Ilha Solteira, 2016. http://hdl.handle.net/11449/138275.
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Orientador: Eudes Borges de AraújoResumo: Filmes finos de Pb0,91La0,09(Zr0,65Ti0,35)O3 (PLZT) foram preparados sobre substratos Pt/TiO2/SiO2/Si(100), usando um método químico baseado no processo Pechini, com objetivo de estudar a supressão da fase pirocloro e a estabilização da fase perovskita. Pós de PLZT preparados por reação do estado sólido foram utilizados como principal fonte de íons Pb2+, La2+, Zr4+ e Ti4+ pela dissolução em solução ácida. A obtenção de resinas poliméricas estáveis com diferentes excessos de chumbo foi possível preparando-se separadamente as resinas de PLZT e PbO seguido de posterior mistura e homogeneização à temperatura ambiente.
Abstract: Pb0,91La0,09(Zr0,65Ti0,35)O3 (PLZT) thin films were prepared on Pt/TiO2/SiO2/Si(100) substrates by using a chemical method based on Pechini process to study the pyrochlore phase suppression and to stabilizing the perovskite phase. PLZT powders prepared by solid state reaction were used as source of Pb2+, La2+, Zr4+ and Ti4+ ions by its dissolution in acid solution.
Doutor
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Freire, Rafael Luiz Heleno [UNESP]. "Síntese e propriedades físicas de filmes ferroelétricos do sistema PLZT." Universidade Estadual Paulista (UNESP), 2012. http://hdl.handle.net/11449/91956.
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freire_rlh_me_ilha.pdf: 1499812 bytes, checksum: c68dc0f0c8070f1cf78c922fae42e2df (MD5)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
O titanato zirconato de chumbo dopado com lantânio, dado convencionalmente pela fórmula estequiométrica Pb1− x Lax ( Zry ; Ti1− y ) 1− x / 4 O3 , com x = 0,09 e y = 0,65, também conhecido como PLZT 9/65/35, é um importante sistema ferroelétrico relaxor devido as suas propriedades dielétricas, elétricas e eletroóticas. Sendo um ferroelétrico, exibe, também, propriedades tais como piezo e piroeletricidade, dependendo apenas das proporções em que são preparados. Logo, esse sistema é bastante interessante para uma gama de aplicações tecnológicas. Na forma de filmes finos, a composição PLZT 9/65/35 tem sido amplamente estudada e preparada pelos mais diversos métodos. Neste trabalho propõe-se a síntese de filmes finos ferroelétricos da composição PLZT 9/65/35 pelo método dos precursores óxidos, a fim de se compreender a dinâmica dos processos de cristalização e, também, avaliar suas propriedades físicas, como permissividade elétrica e histerese ferroelétrica. A intenção, assim, é colaborar com as informações presentes na literatura sobre as propriedades de filmes finos de PLZT 9/65/35
The lead zirconate titanate doped with lanthanum, conventionally given by stoichiometric formula Pb1− x Lax ( Zry ; Ti1− y ) 1− x / 4 O3 , with x=0,09 and y=0,65, also known as PLZT 9/65/35, is an important relaxor ferroelectric system due to its dielectric, electrical and electrooptical properties. Being a ferroelectric material exhibits also properties such as piezo- and piroelectricity, depending upon the extent to which they are prepared. Therefore, this system is very interesting for a range of technological applications. In the thin films format, the composition PLZT 9/65/35 has been widely studied and prepared by several methods. In this project it is proposed the synthesis of thin films of such material by the oxide precursor method in order to understand the dynamics of crystallization process and also to evaluate their physical properties like electrical permittivity and ferroelectric hysteresis. The intention, thus, is collaborate with the information presented in the literature about the properties of PLZT 9/65/35 thin films
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Tavernor, Andrew. "Modelling relaxor ferroelectrics." Thesis, University of Leeds, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305874.
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Melo, Michael de [UNESP]. "Structural and local physical properties of relaxor ferroelectric thin films." Universidade Estadual Paulista (UNESP), 2017. http://hdl.handle.net/11449/151761.
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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Polycrystalline thin films of Pb0.91La0.09Zr0.65Ti0.35O3 (PLZT9/65/35) and Sr0.75Ba0.25Nb2O6 (SBN75) were prepared by the chemical polymeric routine in order to investigate their physical properties at the macro- and nanoscale. X-ray diffraction (XRD), piezoresponse force microscopy (PFM), and scanning electron microscopy (SEM) were used as investigative tools. PLZT9/65/35 and SBN75 thin films have exhibited perovskite and tungsten bronze crystal structure at room temperature, as it was expected in this nominal composition for these relaxor ferroelectric materials. In addition, Rietveld method of the crystalline structure has revealed the thickness dependence of the crystallite size, grain size, and microstrain. The transition temperature of SBN thin film showed to shift to lower temperatures, suggesting the presence of a higher defect concentration, such as oxygen vacancies, chemical disorder, and lattice defects in this film. SEM has exhibited the porosity features in both thin films and has confirmed the existence of chemical elements (such as oxygen, niobium, lanthanum, strontium, platinum, silicon and barium) in film surface and near the substrate. Ferroelectric properties have been investigated by PFM and the results have suggested a thickness and crystallite size dependence of the piezoelectric response. Also in this work, the dynamic of ferroelectric domain switching and the induced domain relaxation were studied using the switching spectroscopy PFM (SS-PFM) in both relaxor systems as a function of variable DC applied voltages and pulse durations.
Filmes policristalinos de Pb0,91La0,09Zr0,65Ti0,35O3 (PLZT9/65/35) e de Sr0,75Ba0,25Nb2O6 (SBN75) foram preparados por uma rotina química polimérica para investigarmos as suas propriedades em nano- e macroescala. Difração de raios-X (DRX), microscopia de força atômica de piezoresposta (PFM), e microscopia eletrônica de varredura (SEM), foram utilizados como ferramentas investigativas. Os filmes finos de PLZT9/65/35 e de SBN75 exibiram estrutura peroviskita e tungstênio bronze, respectivamente, conforme esperado à temperatura ambiente e na composição nominal para estes materiais ferroelétricos relaxores. Além disso, o refinamento de Rietveld da estrutura revelou a dependência do tamanho do cristalito e do microstrain com a espessura. A temperatura de transição de fase do filme de SBN mostrou um deslocamento para valores menores de temperatura, sugerindo a presença de concentração de defeitos, tais como vacâncias de oxigênio, desordem química e defeitos de rede, maior no filme de SBN. Microscopia eletrônica de varredura (SEM) exibiu o caráter poroso de ambos os filmes. Propriedades ferroelétricas desses filmes foram investigados por meio da técnica de PFM. A piezoresposta mostrou ter uma dependência em função do tamanho do cristalito e da espessura. Neste trabalho, a dinâmica de reversão de domínios ferroelétricos e a relaxação de domínios induzidos foram estudados por meio do uso da espectroscopia de chaveamento (SS-PFM) em ambos os sistemas em função da tensão DC e do tempo de duração do pulso.
CNPq: 232241/2014-7
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Nealon, Thomas Anthony. "The properties of ferroelectric relaxors." Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329982.
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Nahas, Yousra. "Gauge theory for relaxor ferroelectrics." Phd thesis, Ecole Centrale Paris, 2013. http://tel.archives-ouvertes.fr/tel-01003357.
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Concomitantly with lattice disorder, there is a discrepancy between local and global scales in relaxor ferroelectrics, in that structural distortions occurring at the local scale are not reflected in the average global structure which remains cubic. There is an absence of direct implementation of the local symmetry in the modeling of relaxors, despite its considerable, but often unacknowledged, ability to encode local features. Central to the thesis is an explicit account for local gauge symmetry within the first-principles-derived effective Hamiltonian approach. The thesis thus aims to consider how an extended symmetry allowing independent transformations at different points in space can effectively bridge local features and macroscopical properties. An underlying question the thesis also seeks to answer is whether the disorder-induced non-trivial interplay between local and global scales can be described from a topological point of view
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Melo, Michael de. "Structural and local physical properties of relaxor ferroelectric thin films /." Ilha Solteira, 2017. http://hdl.handle.net/11449/151761.
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Orientador: Eudes Borges de AraújoResumo: Polycrystalline thin films of Pb0.91La0.09Zr0.65Ti0.35O3 (PLZT9/65/35) and Sr0.75Ba0.25Nb2O6 (SBN75) were prepared by the chemical polymeric routine in order to investigate their physical properties at the macro- and nanoscale. X-ray diffraction (XRD), piezoresponse force microscopy (PFM), and scanning electron microscopy (SEM) were used as investigative tools. PLZT9/65/35 and SBN75 thin films have exhibited perovskite and tungsten bronze crystal structure at room temperature, as it was expected in this nominal composition for these relaxor ferroelectric materials. In addition, Rietveld method of the crystalline structure has revealed the thickness dependence of the crystallite size, grain size, and microstrain. The transition temperature of SBN thin film showed to shift to lower temperatures, suggesting the presence of a higher defect concentration, such as oxygen vacancies, chemical disorder, and lattice defects in this film. SEM has exhibited the porosity features in both thin films and has confirmed the existence of chemical elements (such as oxygen, niobium, lanthanum, strontium, platinum, silicon and barium) in film surface and near the substrate. Ferroelectric properties have been investigated by PFM and the results have suggested a thickness and crystallite size dependence of the piezoelectric response. Also in this work, the dynamic of ferroelectric domain switching and the induced domain relaxation were studied using the switching spectroscopy PFM (SS-PFM) in both r... (Resumo completo, clicar acesso eletrônico abaixo)
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Kiselev, Dmitry. "Piezoresponse force microscopy of ferroelectric relaxors." Doctoral thesis, Universidade de Aveiro, 2010. http://hdl.handle.net/10773/3609.
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Doutoramento em Ciência e Engenharia de MateriaisNesta tese, ferroeléctricos relaxor (I dont know uf the order is correct) de base Pb das familias (Pb,La)(Zr,Ti)O3 (PLZT), Pb(Mg1/3,Nb2/3)O3-PbTiO3 (PMN-PT), Pb(Zn1/3,Nb2/3)O3-PbTiO3 (PZN-PT) foram investigados e analisados. As propriedades ferroeléctricas e dieléctricas das amostras foram estudadas por métodos convencionais de macro e localmente por microscopia de força piezoeléctrica (PFM). Nos cerâmicos PLZT 9.75/65/35 o contraste da PFM à escala nanometrica _ foi investigado em função do tamanho e orientação dos grãos. Apurou-se que a intensidade do sinal piezoeléctrico das nanoestruturas diminui com o aumento da temperatura e desaparece a 490 K (La mol. 8%) e 420 K (9,5%). Os ciclos de histerese locais foram obtidos em função da temperatura. A evolução dos parâmetros macroscópicos e locais com a temperatura de superfície sugere um forte efeito de superfície nas transições de fase ferroeléctricas do material investigado. A rugosidade da parede de domínio é determinada por PFM para a estrutura de domínio natural existente neste ferroeléctrico policristalino. Além disso, os domínios ferroeléctricos artificiais foram criados pela aplicação de pulsos eléctricos à ponta do condutor PFM e o tamanho de domínio in-plane foi medido em função da duração do pulso. Todas estas experiências levaram à conclusão de que a parede de domínio em relaxors do tipo PZT é quase uma interface unidimensional. O mecanismo de contraste na superfície de relaxors do tipo PLZT é medido por PFMAs estruturas de domínio versus evolução da profundidade foram estudadas em cristais PZN-4,5%PT, com diferentes orientações através da PFM. Padrões de domínio irregulares com tamanhos típicos de 20-100 nm foram observados nas superfícies com orientação <001> das amostras unpoled?. Pelo contrário, os cortes de cristal <111> exibem domínios regulares de tamanho mícron normal, com os limites do domínio orientados ao longo dos planos cristalográficos permitidos. A existência de nanodomínios em cristais com orientação <001> está provisoriamente (wrong Word) atribuída à natureza relaxor de PZN-PT, onde pequenos grupos polares podem formar-se em coindições de zero-field-cooling (ZFC). Estes nanodomínios são considerados como os núcleos do estado de polarização oposta e podem ser responsáveis pelo menor campo coercitivo para este corte de cristal em particular. No entanto, a histerese local piezoelétrica realizada pelo PFM à escala nanométrica indica uma mudança de comportamento de PZN-PT semelhante para ambas as orientações cristalográficas investigadas. A evolução das estruturas de domínio com polimento abaixo da superfície do cristal foi investigada. O domínio de ramificações e os efeitos de polarização de triagem após o polimento e as medições de temperatura têm sido estudados pela PFM e pela análise SEM. Além disso, verificou-se que a intensidade do sinal piezoeléctrico a partir das estruturas de nanodomínio diminui com o aumento da temperatura, acabando por desaparecer aos 430 K (orientaçáo <111>) e 470 K (orientação <100>). Esta diferença de temperatura nas transições de fase local em cristais de diferentes orientações é explicada pelo forte efeito de superfície na transição da fase ferroelétrica em relaxors.A comutação da polarização em relaxor ergódico e nas fases ferroeléctricas do sistema PMN-PT foram realizadas pela combinação de três métodos, Microscopia de Força Piezoeléctrica, medição de um único ponto de relaxamento eletromecânico e por ultimo mapeamento de espectroscopia de tensão. A dependência do comportamento do relaxamento na amplitude e tempo da tensão de pulso foi encontrada para seguir um comportamento logarítmico universal com uma inclinação quase constante. Este comportamento é indicativo da progressiva população dos estados de relaxamento lento, ao contrário de uma relaxação linear na presença de uma ampla distribuição do tempo de relaxamento. O papel do comportamento de relaxamento, da não-linearidade ferroeléctrica e da heterogeneidade espacial do campo na ponta da sonda de AFM sobre o comportamento do ciclo de histerese é analisada em detalhe. Os ciclos de histerese para ergódica PMN- 10%PT são mostrados como cineticamente limitados, enquanto que no PMN, com maior teor de PT, são observados verdadeiros ciclos de histerese ferroeléctrica com viés de baixa nucleação.
In this thesis, Pb-based relaxor ferroelectrics of the (Pb,La)(Zr,Ti)O3 (PLZT), Pb(Mg1/3,Nb2/3)O3-PbTiO3 (PMN-PT), Pb(Zn1/3,Nb2/3)O3-PbTiO3 (PZN-PT) families were investigated and analyzed. Ferroelectric and dielectric properties of the samples were studied by conventional macroscopic methods and locally by piezoresponse force microscopy (PFM). In PLZT 9.75/65/35 ceramics the nanoscale PFM contrast was investigated as a function of grain size and grain orientation. It was found that the intensity of piezoresponse signal from nanodomain structure decreases with temperature and it disappears at 490 K (La mol. 8%) and 420 K (9.5%). Local hysteresis loops were obtained as a function of temperature. The evolution of the macroscopic and local parameters with temperature suggests strong surface effect on ferroelectric phase transition in the investigated materials. The domain wall roughness is determined with PFM for the natural domain structure existing in this polycrystalline ferroelectric. Besides, artificial ferroelectric domains were created by application of voltage pulses to the conducting PFM tip, and the in-plane domain size was measured as a function of pulse duration. All these experiments result in the conclusion that the domain wall in PZT-type relaxors is quasi one-dimensional interface. The mechanism of the surface contrast in PLZT-type relaxors is uncovered by PFM. Domain structures vs. depth evolution was studied in PZN-4.5%PT crystals with different orientation via PFM. Irregular domain patterns with the typical sizes 20-100 nm were observed on the (001)-oriented surfaces of unpoled samples. On the contrary, (111) crystal cuts exhibit normal micron-size regular domains with the domain boundaries directed along allowed crystallographic planes. The existence of nanodomains in (001)-oriented crystals is tentatively attributed to the relaxor nature of PZN-PT where small polar clusters may form under zero-field-cooling (ZFC) conditions. These nanodomains are considered as the nuclei of the opposite polarization state and can be responsible for the smaller coercive field for this particular crystal cut. However, local piezoelectric hysteresis performed by PFM on the nanometer scale indicates similar switching behavior of PZN-PT for both investigated crystallographic orientations. Evolution of the domain structures with polishing below the crystal surface has been investigated. The domain branching and polarization screening effects after polishing and temperatures measurements have been studied by PFM and SEM analysis. In addition, it was found what the intensity of piezoresponse signal from nanodomain structures decreases with temperature and finally disappears at 430 K (<111> orientation) and 470 K (<100> orientation). This difference of the temperature of local phase transitions for crystals of different orientaions is explained by strong surface effect on ferroelectric phase transition in relaxors. Polarization switching in ergodic relaxor and ferroelectric phases in the PMNPT system is studied using Piezoresponse Force Microscopy, single point electromechanical relaxation measurements, and voltage spectroscopy mapping. The dependence of relaxation behavior on voltage pulse amplitude and time was found to follow a universal logarithmic behavior with a nearly constant slope. This behavior is indicative of the progressive population of slow relaxation states, as opposed to a linear relaxation in the presence of a broad relaxation time distribution. The role of relaxation behavior, ferroelectric non-linearity, and the spatial inhomogeneity of the tip field on hysteresis loop behavior is analyzed in detail. The hysteresis loops for ergodic PMN-10%PT are shown to be kinetically limited, while in PMN with larger PT content, true ferroelectric hysteresis loops with low nucleation biases are observed.
FCT - SFRH/BD/22391/2005
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Liu, Tieqi. "Electromechanical Behavior of Relaxor Ferroelectric Crystals." Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4881.
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Relaxor ferroelectric PZN-xPT and PMN-xPT single crystals exhibit extraordinary electromechanical properties. They are under development for applications in sensors, actuators and transducers. The polarization switching and phase transition behavior of PZN-4.5%PT and PMN-32%PT single crystals under external loading has been investigated. Experimental investigation elucidates the polarization switching and phase transition behavior of relaxor ferroelectric crystals at different orientation cuts under combined temperature, electric field and stress loading. These crystals exhibit strong orientation dependence of electromechanical properties, and the applied fields all affect the poling and phase states of the crystals. Based on experimental investigation, crystal variant modeling was developed to compute the piezoelectric properties of multi-domain crystals at different orientation cuts from a set of properties for the single domain. Thermodynamics and work-energy analysis of field induced phase transitions in these single crystals sheds light on the phase transition mechanism of ferroelectric crystals. Fracture behavior of relaxor single crystals under non-uniform electric fields at a partial electrode edge has also been measured and analyzed.
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Hilton, Andrew David. "TEM studies of relaxor ferroelectric materials." Thesis, University of Essex, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328755.
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Zhou, Donghua. "Multinuclear NMR studies of relaxor ferroelectrics." W&M ScholarWorks, 2003. https://scholarworks.wm.edu/etd/1539623422.
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Multinuclear NMR of 93Nb, 45Sc, and 207Pb has been carried out to study the structure, disorder, and dynamics of a series of important solid solutions: perovskite relaxor ferroelectric materials (1-x) Pb(Mg1/3Nb 2/3)O3-x Pb(Sc1/2Nb1/2)O 3 (PMN-PSN).;93Nb NMR investigations of the local structure and cation order/disorder are presented as a function of PSN concentration, x. The superb fidelity and accuracy of 3QMAS allows us to make clear and consistent assignments of spectral intensities to the 28 possible nearest B-site neighbor (nBn) configurations, (NMg, NSc, NNb), where each number ranges from 0 to 6 and their sum is 6. For most of the 28 possible nBn configurations, isotropic chemical shifts and quadrupole product constants have been extracted from the data. The seven configurations with only larger cations, Mg 2+ and Sc3+ (and no Nb5+) are assigned to the seven observed narrow peaks, whose deconvoluted intensities facilitate quantitative evaluation of, and differentiation between, different models of B-site (chemical) disorder. The "completely random" model is ruled out and the "random site" model is shown to be in qualitative agreement with the NMR experiments. to obtain quantitative agreement with observed NMR intensities, the random site model is slightly modified by including unlike-pair interaction energies.;To date, 45Sc studies have not been as fruitful as 93Nb NMR because the resolution is lower in the 45Sc spectra. The lower resolution of 45Sc spectra is due to a smaller span of isotropic chemical shift (40 ppm for 45Sc vs. 82 ppm for 93Nb) and to the lack of a fortuitous mechanism that simplifies the 93Nb spectra; for 93Nb the overlap of the isotropic chemical shifts of 6-Sc and 6-Nb configurations results in the alignment of all the 28 configurations along only seven quadrupole distribution axes.;Finally we present variable temperature 207Pb static, MAS, and 2D-PASS NMR studies. Strong linear correlations between isotropic and anisotropic chemical shifts show that Pb-O bonds vary from more ionic to more covalent environments. Distributions of Pb-O bond lengthes are also quantitatively described. Such distributions are used to examine two competing models of Pb displacements; the shell model and the unique direction model. Only the latter model is able to reproduce the observed Pb-O distance distribution.
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Brouwer, William J. "Nuclear magnetic resonance studies of relaxor ferroelectrics." W&M ScholarWorks, 2005. https://scholarworks.wm.edu/etd/1539623478.
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This work is devoted to the study of local order in the ferroelectric PbSc1/2Ta1/2O3 (PST) and relaxor ferroelectric solid solutions (1-x)PbSC2/3W1/3O3-(x)PbTiO 3 (PSW-PT), (1x)PbSC2/3W1/3O3-(x)PbZrO 3 (PSW-PZ). Novel Magic Angle Spinning (MAS) Solid State Nuclear Magnetic Resonance (SS-NMR) experiments, including Multiple Quantum MAS (MQMAS) and Double Quantum Filtered Satellite Transition (DQF-STMAS), have been performed on these materials. A gamma function model is proposed for the distribution of quadrupole coupling constants, based on the Poissonian nature of atomic displacements. Moments for distributions may be subsequently extracted through agreement between experimental spectra and simulations implemented in novel programs. Simple crystal compound scandium oxide provides a reasonable analogue and assists in spectral interpretation. Support is given to the Random Site (RS) model for atomic ordering in Relaxor Ferroelectrics. Based on point charge calculations, significant lead displacement takes place as well as oxygen octahedral tilting. In June 2004, Donghua Zhou proposed an experimental scheme to expedite the interpretation of experimental spectra for materials such as those studied here and a realization with analysis is given.
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Chu, Fan. "The ferroelectric phase transition in complex perovskite relaxors /." [S.l.] : [s.n.], 1994. http://library.epfl.ch/theses/?nr=1248.
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Bhattacharya, Prodipta. "Solid state NMR studies of ferroelectric relaxor materials." Thesis, University of Warwick, 2005. http://wrap.warwick.ac.uk/66666/.
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Multi-nuclear solid state nuclear magnetic resonance has been used to investigate the local atomic structure of the relaxor ferroelectric materials, lead magnesium niobate titanate (PMN-PT) and sodium potassium bismuth titanate (NKBT). In addition to these two series of materials, numerous precursor and model niobate compounds have also been analysed in order to gain a insight into the structures and phases present in these materials. The PMN-PT series was investigated using 93Nb, 207Pb and 170 NMR techniques. A total of 14 PMN-PT samples, from pure PMN to PMN-90PT, were investigated in order to fully understand the transitions taking place over the entire compositional range. 9~b proved to be the most informative nucleus, owing to its high sensitivity to the changes occurring at the B-site of the perovskite structure. We discovered three distinct niobium environments. We then proposed a new randomsite random-layer model explaining the distribution of the cations among two different layers ß' and ß". The high level of correlation between the theoretical predictions and the experimental results suggests that there are actually two different ways that PMN-PT behaves, one for titanium concentrations less than 25% and the other for concentrations over 25%. This was also clearly visible in our PMN-PT spectra, as a sharp line present in titanium concentrations below 25%, that disappears in the concentrations above 25%. We have also tied in our results with the existing literature on PMN-PT to identify possible links to the dielectric response and phase transitions in the material. NKBT was investigated using both 23Na and 39K MAS NMR techniques. The 23Na data proved most informative and results were obtained at different fields and different spinning speeds. We were then able to extract calculated isotropic chemical shift values and quadrupolar parameters to understand the subtle changes taking place. The preliminary results hint that there are some interesting changes taking place around the morphotropic phase boundary in the material.
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Corbett, Michael H. "Synthesis of thin film relaxor electroceramics and heterostructures." Thesis, Queen's University Belfast, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343205.
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Waeselmann, Naëmi [Verfasser], and Boriana [Akademischer Betreuer] Mihaylova. "Structural transformations in complex perovskite-type relaxor and relaxor-based ferroelectrics at high pressures and temperatures / Naëmi Waeselmann. Betreuer: Boriana Mihaylova." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2012. http://d-nb.info/1024355527/34.
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Zang, Jiadong [Verfasser]. "High-temperature dielectrics based on relaxor ferroelectrics / Jiadong Zang." Aachen : Shaker, 2014. http://d-nb.info/1053904207/34.
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Kircher, Oliver. "Lineare und nichtlineare dielektrische Spektroskopie am Relaxor-Ferroelektrikum-Bleimagnesiumniobat." [S.l.] : [s.n.], 2001. http://ArchiMeD.uni-mainz.de/pub/2001/0136/diss.pdf.
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Welter, Cezar. "Comportamento relaxor de polímeros ferroelétricos submetidos a radiações eletromagnéticas." Universidade Federal de Minas Gerais, 2008. http://hdl.handle.net/1843/ESCZ-7N4GFV.
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Electromagnetic radiation effects onto poly (vinylidene fluoride-trifluoroethylene), P(VDFTrFE) copolymers are studied. It is demonstrated that high energy (gamma radiation, E = 1250 keV ) and low energy (ultraviolet radiation, EUV = 4.88 eV ) ionizing radiation are able to induce a relaxor behavior to equimolar (PVDF-TrFE) ferroelectric copolymer. This is the first scientific report on the use of low energy radiation to induce and study the relaxor behavior in ferroelectric polymers. The experimental technics used to investigate the effects of radiations were: (1) xray diffractometry, to structurally characterize the crystalline phase and to find the relation between crystalline and amorphous phases; (2) differential scanning calorimetry, to analyze the thermal stability of ferro-paraelectric transition and the melting point;(3) thermo-dielectric spectroscopy, to qualify the electric dipoles interactions, that represent the ferroelectric domains of material and its interactions; (4) infrared and ultraviolet spectroscopy, to detect the included chemical changes; and (5) solvent dissolutions to confirm intermolecular chemicals modifications. We demonstrated that the mechanisms responsible for inducing the relaxor behavior under low and high energy radiation are distinct. In the case of gamma radiation, therelaxor behavior is a consequence of the decreasing correlation length between the ferroelectric domains (loss of cooperative ferroelectric effects), due three-dimensional reticulation. In the case of ultraviolet radiation, it is due to the formation of singlet, duplets, and triplets of double (C=C) bounds.Estudamos os efeitos da radiação eletromagnética sobre o copolímero poli(fluoreto de vinilideno ^Ö trifluoroetileno), P(VDF-TrFe). Demonstramos que tanto a radiação ionizante de alta energia (radiação gama, Eg = 1250 keV), quanto a de baixa energia (radiação ultravioleta, EUV = 4.88 eV) são capazes de induzir o comportamento relaxor em um copolímero ferroelétrico contendo 50% molar de monômeros de trifluoretileno. Este é o primeiro trabalho científico que utiliza radiação de baixa energia para a indução e o estudo do efeito relaxor em polímeros ferroelétricos. As técnicas experimentais utilizadas para determinar o estado e as alterações decorrentes das radiações foram: (1) difratometria de raios-X (DRX), na caracterização estrutural da fase cristalina e relação entre fase cristalina e amorfa; (2) calorimetria diferencial de varredura (DSC), na análise de estabilidade térmica da transição de fase ferro-paraelétrica e ponto de fusão; (3) espectroscopia termodielétrica (DETA), para qualificar as interações entre dipolos elétricos que caracterizam os domínios ferroelétricos contidos no material, bem como as interações entre domínios; (4) espectroscopias de infravermelho e ultravioleta (FTIR e UV-VIS), na detecção de alterações químicas induzidas; e (5) dissolução em solvente para a confirmação de alterações químicas intermoleculares. Demonstramos que, apesar de ambas as radiações, de alta e de baixa energia serem capazes de induzir o efeito relaxor, elas o fazem por mecanismos distintos. O efeito relaxor decorre da redução do comprimento de correlação entre os domínios ferroelétricos do material (perda do efeito cooperativo entre domínios), conseqüência do surgimento de retículos tridimensionais e outros radicais no copolímero quando exposto a radiação gama, ou pela formação de singletos, dupletos e tripletos de ligações duplas entre carbonos (C=C) na cadeia polimérica quanto submetido à radiação ultravioleta.
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Zhou, Liqin. "Relaxor behavior of Pb(Fe2/3W1/3)O3 ceramics." Doctoral thesis, Universidade de Aveiro, 1996. http://hdl.handle.net/10773/17561.
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Doutoramento em Engenharia Cerâmica e do VidroThe complex perovskite Pb(Fe213W1fi)O; (PFW) is one of the many ferroelectric relaxors. Although PFW has a low transition temperature around 1S5K, it is used to obtain solid solutions with dielectric parameters adjusted to make multilayer capacitors, meeting appropriate standard specifications. PFW was first synthesized in the late fifties, but, it has received less attention than other ferroelectric relaxors, like Pb(Mgl~Nbz5)O; and Pb(Scl~Taii2)03. In this thesis, diierent interesting aspects of the relaxor properties of PFW ceramics, such as synthesis, aging, ordering and disorde~gw, ere studied, in order to extend the understanding of the relaxation behavior of ferroelectric relaxors. PFW ceramics was successfully synthesized by the columbite precursor method, using the reaction between a prereacted columbite-type compound FezW06 and PbO. Considerable improvements were achieved in relation to the conventional mixed oxide procedure: an almost single phase PFW ceramics (>98%), with high dielectric permittivity value (~,,,=12180, at 10KHz) and dense and uniform microstructure, was obtained. The aging behaviors of diierent stoichiometric, Mn and La modified PFW ceramics were studied. The tungsten deficient samples showed evident aging effects, more pronounced as the tungsten deficiency increased. However, lead deficient samples showed no aging phenomena. Mn doping does not cause marked changes in the maximum of the permittivity E,, the transition temperature TO and the diffuseness coefficient 6, while the aging level increases significantly with increasing the Mn content. La doping results in the decrease o, , E, f the shift of To to lower temperatures and the increase of 6. The aging decreases with increasing the La content up to 5at%. No aging was observed at 5at%. Samples doped with lOat% of La show again aging behavior. Comparing with nonstoichiometric and Mn doped PFW ceramics, the aging of La doped samples is not so strong. In general the aging behavior shows a strong dependence on the frequency, a log-linear hnction of the aging time, and a shift of the dielectric distortion with the aging temperature. The defect dipole pairs, provided by the W vacancies, acceptor and donor defects, with the corresponding compensating defects, couple to the polarization vectors, being suggested to be responsible for the aging process of nonstoichiometric, Mn and La modified PFW ceramics. The structural positions of the defects in the perovskite lattice and the reorientation of the defect dipole pairs, were discussed for the studied compositions and suggested to account for the different aging behavior observed between samples with different defective nature. The ordering of PFW ceramics is difficult to be modified by annealing treatments in air, but the presence of vacancies in the ceramics could si@cantly enhance the rearrangement of B cations. Although no superlattice reflections were detected by either X-ray difliaction (XRD) or transmission electron microscopy (TEM) for air annealed samples, considerable modifications of the dielectric properties were observed after air annealing treatment: the dfiseness of the dielectric permittivity is decreased and the permittivity maximum value is increased. The annealing effect is enhanced with increasing the amount of Mn dopant; it weakens with increasing the La content below 5at%, and the dielectric permittivity and loss factor are almost unchanged after annealig a 5at% La doped sample. Further increase in La content, leads to the annealing effect becoming evident again. The role of the oxygen and lead vacancies, present in Mn and La doped PFW ceramics, respectively, on the annealing process, was proposed and discussed. Sodium doping could easily moe the ordering of PFW ceramics. The superlattice reflections, indexed as {h+i, k+i, 1++ }, were observed in both XRD and TEM diiaction patterns. These reflections were identified to be associated with 1:l type ordering of B cations. The ordering degree increases with increasing the Na content, when NalXat% and decreases, when Na>Xat%. The Na modified PFW ceramics were not single phase. Besides the PFW perovskite phase, a second phase, PbW04, was also observed and its amount increases with increasing the Na content. The effect of the sodium substitutional ions, on enhancing the ordering of the PFW ceramics, was suggested to be due to the weakening of the charge effect, in the ordered regions, caused by the lower valence of Na+ ions, when substituting pb2* ions. The competition between the enhancement of ordering and the formation of PbW04 phase was suggested to be responsible for the decrease of ordering when Na>Xat%. La doping causes a decrease of ordering of PFW perovskite. The effects of Na and La doping on the dielectric properties were also analyzed and discussed. The relaxation behavior of the PFW ceramic compositions studied in this work supports the compositional fluctuation and superparaelectric models proposed to explain the dielectric diffuseness of ferroelectric relaxors.
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Mathan, Nicolas de. "Études structurales de céramiques diélectriques de magnoniobate de plomb Pb(Mg1/3Nb2/3)O3 en fonction de la température." Châtenay-Malabry, Ecole centrale de Paris, 1991. http://www.theses.fr/1991ECAP0157.
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Les céramiques de PbMg1/3Nb2/3O3 (PMN) constituent un modele de relaxor ; leur constante diélectrique présente à Tmax (environ 270 k) un maximum large en fonction de la température ainsi qu'une forte relaxation en fréquence. Ce maximum de la constante diélectrique est attribué à une corrélation polaire des déplacements atomiques qui apparaitrait en dessous de Td (environ 600 k) et dont la longueur de cohérence augmenterait sensiblement au voisinage de Tmax. En diffraction sur poudre, cette corrélation se manifeste par de la diffusion diffuse concentrée au pied des raies. Un blocage de l'évolution structurale se produit en dessous de 180 k environ et, à 5 k, la taille des nanorégions polaires serait proche d'une centaine d'angstroms. Par l'application d'un fort champ électrique à basse température, l'ordre polaire à courte distance est transformé en un ordre polaire à longue distance de symétrie rhomboédrique ; après suppression du champ électrique, cette structure reste stable en dessous de Tt (environ 200 k). Il existe également des régions dont la taille est voisine de 20-40 angstroms et à l'intérieur desquelles la distribution des cations Mg2+ et Nb5+ se ferait selon un ordre 1:1 non stchiométrique. Ceci induit des fluctuations de composition et de charge électrique. Par analogie avec le cas des verres dipolaires, nous pouvons penser que ces fluctuations sont à l'origine du blocage de l'évolution structurale qui se produit en dessous de 190 k.
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Ivanov, Maksim. "Grain size effect on dielectric properties of ferroelectrics and relaxors." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2014. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2014~D_20141230_153112-03380.
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The aim of doctoral dissertation „Grain Size Effect on Dielectric Properties of Ferroelectrics and Relaxors“ by Maksim Ivanov is to investigate, how grain size of ceramics and powders of a few ferroelectrics and relaxors influences macroscopic dielectric properties. The studied materials are powders of a relaxor PbMg⅓Nb⅔O3 (PMN), ceramics of a relaxor with a spontaneous phase transition PbSc½Nb½O3 (PSN), ceramics of a ferroelectric 0.36BiScO3-0.64PbTiO3, and ceramics of Ba2SnO4, which were compared to a better investigated BaSnO3. Investigations were performed in broad frequency (100 Hz – 55 GHz) and temperature (30 K – 1000 K) ranges. Experimental investigations and modelling showed, that bulk properties of relaxor materials are heavily influenced by polar nanoregions, but they do not fully determine them. Morphology of the material (i.e. grain size of ceramics) determines growth and interactions of the nanoregions, thus influencing bulk properties. Moreover, effective medium approximation can explain evolution of dielectric properties of ferroelectrics and relaxors only if dependence of bulk properties on grain size is known. The most interesting result is, that there exist polar entities in ferroelectrics, which are different from ferroelectric domains and are similar to polar nanoregions in relaxors. Their contribution to dielectric permittivity can be comparable to all other contributions. Dimensions of these entities depend on grain size in accordance with Kittel's law.Maksimo Ivanovo daktaro disertacijos tema yra “Grūdų dydžio įtaka dielektrinėms feroelektrikų ir relaksorių savybėms”. Šio darbo tikslas yra ištirti, kaip keramikų ar miltelių grūdų dydis įtakoja makroskopiškai stebimas kelių feroelektrikų bei feroelektrinių relaksorių dielektrines savybes. Tirtos medžiagos yra klasikinio relaksoriuas PbMg⅓Nb⅔O3 (PMN) milteliai, relaksoriaus su savaiminiu feroelektriniu faziniu virsmu PbSc½Nb½O3 (PSN) keramikos, feroelektriko 0.36BiScO3-0.64PbTiO3 keramikos, bei Ba2SnO4 keramiką, kuri buvo palyginta su kiek labiau žinoma BaSnO3 keramika. Tyrimai buvo atlikti plačiame dažnių (100 Hz – 55 GHz) bei temperatūrų (30 K – 1000 K) intervaluose. Eksperimentiniai tyrimai bei modeliavimai parodė, kad polinės nanosritys labai stipriai įtakoja tūrines relaksorių savybes, tačiau jų neapsprendžia. Medžiagos morfologija (antai keramikų grūdų dydis) lemia nanosričių augimą bei tarpusavio sąveikas, tokiu būdų įtakojamos tūrinės savybės. Be to, efektyvios terpės aproksimacija gali paaiškinti feroelektrikų ir relaksorių dielektrinių savybių priklausomybę nuo grūdų dydžio tik, jei žinomas sąryšis tarp dydžio ir tūrinių savybių. Įdomiausia yra tai, kad feroelektrikuose yra objektų, kurie nėra feroelektriniai domenai ir yra panašūs į relaksorių polines nanosritis. Jų indėlis į dielektrinę skvarbą gali būti palyginamas su visų kitų procesų (pvz. domenų sienelių ir polinių modų) indėliais. Šių objektų dydis priklauso nuo grūdų dydžio pagal Kittel'io dėsnį.
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Lima, Elton Carvalho de [UNESP]. "Propriedades dielétricas de cerâmicas relaxoras PMN." Universidade Estadual Paulista (UNESP), 2008. http://hdl.handle.net/11449/92008.
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O presente estudo destina-se à investigação sistemática das propriedades dielétricas de cerâmicas ferroelétricas relaxoras de Pb(Mg1/3Nb2/3)O3 (PMN). A resposta dielétrica em ferroelétricos relaxores, sob diferentes condições de excitações elétricas externas, deve ser considerada com especial atenção, posto que a fenomenologia para os estudos reportados na literatura não está completamente fundamentada. Sob tais considerações, a finalidade do presente trabalho é investigar o comportamento da permissividade dielétrica (e = e´ + i e´´) de cerâmicas PMN em função de campos elétricos AC e DC, em uma ampla faixa de freqüências (20 Hz a 1 MHz) e temperatura (20 K a 800 K). O estudo da dispersão dielétrica com a freqüência foi realizado em termos da relação de Vogel-Fulcher, permitindo a determinação da energia de ativação (Ea) e da temperatura de congelamento (Tf) dos dipolos para a amostra investigada. O comportamento do efeito relaxor em função de campos elétricos externos AC e DC foi avaliado e comparado com os resultados recentes reportados na literatura.
The present study is destined to the systematic investigation of dielectric properties on relaxor ferroelectric lead magnesium niobate Pb(Mg1/3Nb2/3)O3 (PMN). The answer dielectric in ferroelectrics relaxors, under different conditions of external electric excitements, should be considered with special attention, position that the phenomenology for the studies moderated in the literature is not completely based. Under such considerations, the purpose of the present work is to investigate the behavior of the dielectric permittivity ( = ’+ i ”) of ceramic PMN in function of fields electric AC and DC, in a wide interval of frequencies (20 Hz to 1 MHz) and temperature (20 K to 800 K). The study of the dielectric dispersion with the frequency was accomplished in terms of the relationship of Vogel-Fulcher, allowing the determination of the activation energy (Ea) and of the freezing temperature (Tf) of the dipoles for the investigated sample. The behavior of the effect relaxor in function of fields external electric AC and DC was evaluated and compared with the recent results moderated in the literature.
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Lima, Elton Carvalho de. "Propriedades dielétricas de cerâmicas relaxoras PMN /." Ilha Solteira : [s.n.], 2008. http://hdl.handle.net/11449/92008.
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Orientador: Eudes Borges de AraújoBanca: José de Los Santos Guerra
Banca: Jean-Claude M'Peko
Resumo: O presente estudo destina-se à investigação sistemática das propriedades dielétricas de cerâmicas ferroelétricas relaxoras de Pb(Mg1/3Nb2/3)O3 (PMN). A resposta dielétrica em ferroelétricos relaxores, sob diferentes condições de excitações elétricas externas, deve ser considerada com especial atenção, posto que a fenomenologia para os estudos reportados na literatura não está completamente fundamentada. Sob tais considerações, a finalidade do presente trabalho é investigar o comportamento da permissividade dielétrica (e = e' + i e') de cerâmicas PMN em função de campos elétricos AC e DC, em uma ampla faixa de freqüências (20 Hz a 1 MHz) e temperatura (20 K a 800 K). O estudo da dispersão dielétrica com a freqüência foi realizado em termos da relação de Vogel-Fulcher, permitindo a determinação da energia de ativação (Ea) e da temperatura de congelamento (Tf) dos dipolos para a amostra investigada. O comportamento do efeito relaxor em função de campos elétricos externos AC e DC foi avaliado e comparado com os resultados recentes reportados na literatura.
Abstract: The present study is destined to the systematic investigation of dielectric properties on relaxor ferroelectric lead magnesium niobate Pb(Mg1/3Nb2/3)O3 (PMN). The answer dielectric in ferroelectrics relaxors, under different conditions of external electric excitements, should be considered with special attention, position that the phenomenology for the studies moderated in the literature is not completely based. Under such considerations, the purpose of the present work is to investigate the behavior of the dielectric permittivity ( = '+ i ") of ceramic PMN in function of fields electric AC and DC, in a wide interval of frequencies (20 Hz to 1 MHz) and temperature (20 K to 800 K). The study of the dielectric dispersion with the frequency was accomplished in terms of the relationship of Vogel-Fulcher, allowing the determination of the activation energy (Ea) and of the freezing temperature (Tf) of the dipoles for the investigated sample. The behavior of the effect relaxor in function of fields external electric AC and DC was evaluated and compared with the recent results moderated in the literature.
Mestre
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Stoica, Laura Andreea. "Relaxor-PbTiO3 single crystals and polycrystals : processing, growth and characterisation." Thesis, University of Leeds, 2016. http://etheses.whiterose.ac.uk/16259/.
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Acoustic transducers operate using polycrystalline lead zirconate titanate (PZT) since the 1950s’. Recently, relaxor-lead titanate (relaxor-PT) single crystals have been developed and exhibit up to 650% higher piezoelectric charge coefficient and up to 50% higher electromechanical coupling factor, compared with PZT. Transducers built with relaxor-PT crystals show increased bandwidth, lower power consumption and increased sensitivity. Despite the significant advantages over PZT, a growth method for relaxor-PT single crystals that is both economical and able to produce homogeneous, highly dense crystals is yet to be found. Furthermore, one of the most important relaxor-PT solid solution is Mn modified Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3- PbTiO3 due to its thermal stability and low electrical and mechanical losses compared with other relaxor-PT solid solutions. However, the behaviour of Mn in this compound is not fully understood and control of properties, such as the mechanical quality factor, is difficult. The aim of this study was to compare Bridgman and Solid State techniques for growth of single crystalline Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3. Subsequent to this, several Mn modified compositions were designed and investigated to determine the mechanisms by which mechanical and electrical losses are lowered upon Mn incorporation. Bridgman experiments have shown that a 20 mm ø x 60 mm length and highly dense single crystal can be obtained, with (011) the natural growth direction. Seeded Bridgman was also investigated as a method of controlling the orientation of the grown crystal, but was proven challenging due to nucleation of several crystallites. Solid State experiments, which involve attaching a single crystal seed to a polycrystalline matrix and promoting boundary migration of the seed into the matrix, showed that crystal growth is encouraged when a Pb-based interlayer exists in between the seed and matrix. An epitaxially deposited, uniform thin film as interlayer was found particularly beneficial. More research is needed to determine conditions for growth of a single crystal of useful size by Solid State. Analysis of several relaxorPT compositions modified with the same amount of Mn revealed that alterations of the relaxor-PT formulation affects behaviour of the multi-valent Mn which in turn in- fluences electromechanical properties. These findings are of use to the industrial and scientific communities. Crystal growth results indicate Bridgman as suitable method if growth of crystals is desired in a short time frame, whilst Solid State results provide the basis of a new approach for growing relaxor-PT crystals. The study of Mn modified compositions provides new insights into the role of Mn substitution for manipulating the electrical and mechanical properties of complex, relaxor-PT solid solutions.
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Peräntie, J. (Jani). "Electric-field-induced dielectric and caloric effects in relaxor ferroelectrics." Doctoral thesis, Oulun yliopisto, 2014. http://urn.fi/urn:isbn:9789526204406.
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Abstract In this thesis, dielectric and thermal behaviours due to the application of an electric field were studied in relaxor ferroelectric (1−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) and (1−x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 (PZN-PT) systems of great technological importance. Special attention was given to the behaviour of the electric-field-induced phase transitions and electrocaloric effect, which are closely related to the existing and potential applications. Reactive sintering or columbite methods were used to fabricate polycrystalline PMN-PT ceramics with various compositions (x=0−0.3). In addition, commercial PMN-PT single crystals with composition close to the morphotropic phase boundary region were used. A studied PZN-PT crystal composition was grown by solution gradient cooling technique. Materials were mainly studied by means of dielectric and direct temperature measurements. The electrocaloric effect observed in a ceramic PMN-PT system was found to show distinct maximum values close to the thermal depolarization temperatures with low electric fields. The temperature range and magnitude of the electrocaloric effect was significantly expanded to high temperatures with increasing electric fields due to the contribution of polar nanoregions. The maximum electrocaloric temperature change was in the range of 0.77−1.55 °C under an electric field of 50 kV/cm. In addition, temperature change measurements on depoled PMN-0.13PT ceramics demonstrated that the electrocaloric effect is accompanied with an irreversible part below its depolarization temperature due to hysteresis loss and a possible phase transition type response related to the evolution of the macroscopic polarization. An electric field application to the <001> and <011> directions in PMN-PT crystals was found to cause distinct anomalies in the dielectric and temperature change responses. These anomalies were attributed to the complex polarization rotation routes and different phase stability regions in the electric-field-temperature phase diagrams of PMN-PT. Furthermore, measurements on PMN-PT crystals provided the first direct indications of a temporarily reversed electrocaloric effect with an increasing electric field. In addition, the measured electrocaloric trends in PZN-PT crystal were reproduced by a simple lattice model and mean-field approximation around the transition temperature. This demonstrated that the electrocaloric effect is driven mainly by the dipolar entropy loweringTiivistelmä Tässä työssä tutkittiin dielektristen ominaisuuksien ja lämpötilan käyttäytymistä teknologisesti merkittävissä (1−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) ja (1−x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 (PZN-PT) ferrosähköisissä relaksorimateriaaleissa sähkökentän vaikutuksen alaisena. Tutkimuksen erityishuomion kohteena olivat sähköisesti indusoidut faasimuutokset sekä sähkökalorinen ilmiö, jotka liittyvät läheisesti nykyisiin sekä tulevaisuuden sovellutuksiin. Monikiteisiä PMN-PT keraamikoostumuksia (x=0−0,3) valmistettiin sekä reaktiivisella sintrauksella että kolumbiittimenetelmällä. Lisäksi tutkimuksessa käytettiin kaupallisia PMN-PT erilliskiteitä, joiden koostumus on lähellä morfotrooppista faasirajaa. Työssä käytetty PZN-PT erilliskide kasvatettiin jäähdyttämällä korkean lämpötilan liuoksesta. Materiaaleja tutkittiin pääosin lämpötilan ja dielektristen ominaisuuksien mittauksilla. Kun PMN-PT keraamisysteemiin kohdistettiin alhainen sähkökenttä, sähkökalorisen ilmiön selkeä maksimiarvo havaittiin lähellä materiaalin termistä depolarisaatiolämpötilaa. Suuremmilla sähkökentän arvoilla sähkökalorinen ilmiö voimistui ja sen lämpötila-alue laajeni korkeampiin lämpötiloihin polaaristen nanoalueiden kytkeytymisen vuoksi. Sähkökalorisen lämpötilamuutoksen maksimi vaihteli välillä 0,77−1,55 °C sähkökentän arvolla 50 kV/cm. Lisäksi lämpötilamittaukset depoolatulle PMN-0,13PT koostumukselle osoittivat, että sähkökalorisen ilmiön ohella materiaalissa esiintyy makroskooppisen polarisaation muodostumiseen liittyvä palautumaton lämpöenergia depolarisaatiolämpötilaa pienemmissä lämpötiloissa hystereesihäviön ja mahdollisen faasimuutoksen vaikutuksesta. PMN-PT erilliskiteiden dielektrisyys- ja lämpötilavasteessa havaittiin selkeitä muutoksia sähkökentän vaikuttaessa <001> ja <011> kidesuuntiin. Nämä muutokset ovat selitettävissä PMN-PT:n polarisaation kompleksisten rotaatiosuuntien ja erityyppisten sähkökenttä-lämpötila -faasidiagrammien stabiilisuusalueiden avulla. PMN-PT kiteiden mittauksissa havaittiin myös ensimmäinen suora osoitus väliaikaisesti käänteisestä sähkökalorisesta ilmiöstä sähkökentän kasvaessa. Lisäksi mitatut PZN-PT erilliskiteen sähkökaloriset ominaisuudet transitiolämpötilan läheisyydessä pystyttiin pääpiirteittäin mallintamaan käyttämällä yksinkertaista hilamallia ja keskimääräisen kentän approksimaatiota. Mallinnuksen mukaan sähkökalorinen ilmiö aiheutuu pääasiassa sähköisesti indusoidusta dipolientropian alenemisesta
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Le, Goupil Florian. "Electrocaloric effect in ferroelectric relaxors : the road to solid-state cooling." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/39350.
Full textAbstract:
This thesis describes the potential of relaxor ferroelectrics for solid state cooling based on the electrocaloric effect. The core of this investigation is to identify the reliable methods to correctly evaluate the electrocaloric effect and develop materials with the properties required for commercial electrocaloric cooling. A thorough review of the state-of-the-art electrocaloric research reveals that too many research groups still rely on the indirect evaluation of the electrocaloric effect (ECE) from polarization measurements and highlights the need for direct ECE measurements. A direct electrocaloric effect measurement set-up based on a modified-differential scanning calorimeter, allowing the acquisition of both ther- mal (ECE, heat capacity) and electrical (P-E loops, leakage current) information simultaneously, has successfully been constructed and benchmarked. Direct ECE measurements have been performed on normal ferroelectrics, such as barium titanate, but also well-known relaxor ferroelectrics, such as the PMN- PT system, for fundamental understanding of the electrocaloric effect. These results highlight the importance of the polar direction of the electrocaloric mate- rials with regard to the direction of applied electric field. A region with negative ECE, which could be exploited to increase the efficiency of electrocaloric cooling cycles, has been identified for < 001 > -oriented PMN-30PT by both direct and indirect measurements. This negative ECE is observed in the vicinity of the low temperature field-induced structural phase transition, which forms intermediate lower-symmetry monoclinic phases. The occurrence of this phenomenon requires the combination of several parameters related to the direction of application of the electric field. The results on PMN-PT also show how the chemical disorder in ferroelectric relaxors provides important entropy changes over the ferroelectric to paraelectric transition which enables an extended cooling regime as the ECE maximum can be extended over several tens of degrees. Direct ECE measurements have therefore been performed on novel relaxor fer- roelectrics, including perovskite, Aurivillius phase and tungsten bronze structures, with a focus on lead-free, for environmental purposes, highly disordered materi- als. For most of these systems, the direct ECE measurement presented here are the first ever reported. The presence of a dual electrocaloric peak, sometimes far above the ferroelectric to paraelectric transition, is confirmed in all the studied relaxor ferroelectrics. This peak was attributed to the extra contribution to the field-induced entropy change by the polar nanodomains. The presence of this ex- tra ECE peak confirms the great potential of relaxor ferroelectrics for solid-state electrocaloric cooling over a range of temperature broad enough for commercial applications. Comparisons between direct and indirect measurements are performed on nu- merous systems throughout this thesis, in order to identify the domain of validity of the indirect method still overly used in the literature. It is shown that the indi- rect ECE method, although it gives satisfactory results for normal ferroelectrics, is unreliable for strong relaxor ferroelectrics above the ferroelectric to paraelectric phase transition, where the dual peak is observed by direct measurements. These limitations are attributed to the inability of the indirect method to account for the field-induced entropy contribution of the polar nanodomains to the electrocaloric effect.
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Lehnen, Peer. "Relaxoreigenschaften von Strontium-Barium-Niobat - Relaxor Properties of Strontium-Barium-Niobate." Gerhard-Mercator-Universitaet Duisburg, 2001. http://www.ub.uni-duisburg.de/ETD-db/theses/available/duett-12132001-102821/.
Full textAbstract:
In the present thesis the relaxor properties of the tungsten-bronze ferroelectric material strontium-barium niobate Sr1-wBawNb2O6 (SBN) are investigated. SBN is a very good experimental realization of the three-dimensional random-field Ising model (3d RFIM). The quenched random fields (RF) originate from charge disorder and can be enhanced by doping with Ce3+. They are responsible for the formation of polar nanoclusters in the paraelectric phase. In order to study the critical behavior of SBN, linear birefringence (LB) and second harmonic generation (SHG) have been measured as a function of temperature. Within an Ornstein-Zernike analysis of the LB data the autocorrelation function, <P2>, was determined, whereas the dipolar correlation length was obtained from the SHG data. They suggest that, due to its intrinsic disorder, pure SBN does not belong to the 3d Ising universality class. Doping with Ce3+ions, which seem to generate RFs, enhances the relaxor properties. The critical exponents v and y of SBN:Ce shift against those of the 3d RFIM. The domain morphology of SBN:Ce has been investigated by piezoelectric force microscopy (PFM). Fractal-like shaped zero-field cooled nanodomains are observed. Their size distribution can be described by a power law with exponential cutoff in accordance with prediction for the RFIM. It was measured for the first time in a RF system. The temperature and field induced evolution of natural and written domains has been studied with PFM, LB and SHG measurements. It reveals a very slow relaxation from a macrodomain into a depolarized multidomain state (and vice versa) even above TC. This hints at strong pinning forces due to quenched RFs. They are also responsible for the observed aging in poled SBN and the field induced cluster percolation above TC measured with SH-hysteresis. The domains can be considered as a "thick" phase grating for SH-diffraction. The Bragg-regime diffraction efficiency reflects the temperature and field induced change of the averaged domain sizes in the system.
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Shi, Yuping, and 史玉平. "On polarization physics and electrocaloric effect in normal and relaxor ferroelectrics." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2012. http://hub.hku.hk/bib/B49617989.
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Switchable polar properties of ferroelectric and multiferroic nanostructures are ideal to further diversify applications of mainstream semiconductors. Recent breakthroughs in Scanning Probe Microscopy (SPM) have enabled tailoring of polar domain structures at the nanoscale, which is critical to fabricate polarization-based devices. However, highly inhomogeneous electric fields of biased SPM-tips complicate polarization physics in ferroelectrics and multiferroics. Also, typical diffused phase transition in relaxor bulks originates from coupled inhomogeneities of intrinsic polar nanoregions (PNRs). In this thesis, anisotropic and time-dependent mechanisms were developed to study SPM-tip poled polarization switching in ferroelectric and multiferroic thinfilms. Moreover, frequency-related PNR thermodynamics and its effect on electrocaloric effect of locally disordered relaxors were modeled.
Firstly, a three dimensional model was established to clarify tip-poling effect on ferroelectric domain nucleation and growth. The concept of “domain shape invariance” was confirmed through constant aspect ratio obtained for conic ferroelectric nucleus. This domain aspect ratio was found to abruptly decrease under the depolarization effect, saturating domain radius. Further increasing tipvoltage could drive longitudinal breakdown of already reverted domains throughout film thickness.
Subsequently, tip-activated evolution of domain wall width in ferroelectric and multiferroic thinfilms was studied via extended Kittle’s law, which included anisotropic and dynamic effects arising from tip-fields. Our calculation results showed that wall width in LiNbO3 varied slightly in an initial stage, followed by a drastic change. This wall variation corresponded to three varying regions of coercive field. Besides, we highlighted three polarization switching modes in BaTiO3 - absence, activation and nonactivation mode. Importantly, distinct switching modes, i.e., breakdown mode of 71° domain switching and activation mode of 180°/109° switching, were revealed to fundamentally control filmorientation dependent multipolarization switching sequence in BiFeO3.
Thirdly, Pauli’s mater theory was utilized to bridge microscopic evolution of PNRs and characteristic properties of Pb(Mg1/3Nb2/3)O3 (PMN) relaxors. Temperature dispersion and frequency dependence of PMN dielectric susceptibility were related to nonlinear PNR dynamics over a broad temperature interval. We could not validate PNR-volume predictions of percolation theory above the freezing temperature, but suggest a gradual saturation of PNR volume at lower temperatures. Besides, observed deviations of relaxor permittivity from the Curie-Weiss law were attributed to thermal effects on PNR dynamics and resultant polarization rotations. Furthermore, time-dependent PNR dynamics was proposed to study strong frequency dependence of typical relaxor behaviors. It was implied that frequency effect on PNR coercive field was governed by classic Merz’s-switching, leading to suitability of Vogel-Fulcher law for relaxors bulks.
Last but not least, above-mentioned framework for PMN relaxors was incorporated with Landau-Ginzburg-Devonshire thermodynamics and Maxwell relation to better understand recently observed giant electrocaloric (EC) effect of relaxor thinfilms, which is promising for solid-state refrigeration. Three contributions were found to dominate relaxor EC response: temperature-dependent dielectric dispersion, inverse pyroelectric effect and thermally enhanced dielectric stiffness. We emphasized that the EC material with larger dielectric stiffness and smaller correlation length could extend its enormous EC response above Curie temperature. Finally, potential approaches, e.g., by manipulating shape, volume and density of PNRs, were suggested to engineer the EC enhancement in relaxor nanostructures.published_or_final_version
Mechanical Engineering
Master
Master of Philosophy
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Cavalheiro, Alberto Adriano [UNESP]. "Influência dos dopantes potássio e lítio na cerâmica relaxora niobato de chumbo e magnésio (PMN)." Universidade Estadual Paulista (UNESP), 2002. http://hdl.handle.net/11449/102590.
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cavalheiro_aa_dr_araiq.pdf: 6472595 bytes, checksum: e04161cc1c7b719e9fdf747d97469e9f (MD5)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Este trabalho se focaliza na obtenção da cerâmica relaxora PMN com temperatura de máxima constante dielétrica se situando próximo à temperatura ambiente, alta constante dielétrica e valores de perda dielétrica baixos. A influência dos dopantes potássio e lítio durante a síntese dos pós e o processamento da cerâmica PMN constitui uma grande contribuição para a pesquisa deste tipo de material. Os pós de PMN foram sintetizados utilizando a rota da columbita associada ao método de coprecipitação de chumbo. O monitoramento da formação da fase columbita foi acompanhado por DRX. O refinamento de estrutura, o cálculo do tamanho médio de cristalito e a microdeformação de rede foram executadas utilizando o método de Rietveld. Além disso, as amostras foram caracterizadas por TG/DTA, BET e MEV. Diferentemente do lítio, o potássio provoca a elevação da temperatura de formação da fase MgNb2O6 (MN), mas isto não interfere na obtenção do precursor monofásico até a concentração de 2,0%mol de dopante. Para pós de MN calcinados a 900ºC por 2 horas, a presença dos dopantes atenuam a microdeformação de rede e aumentam o tamanho médio de cristalito e, conseqüentemente ocorre a formação de partículas secundárias. Os valores de tamanho médio de cristalito das amostras de PMN dopadas com lítio, calcinadas a 800ºC por 2 horas, são maiores do que para as amostras dopadas com potássio. Nesta condição, a adição de lítio também acarreta crescimento de partículas e aglomeração dos pós. Durante a sinterização, as amostras dopadas com potássio apresentaram tamanho de grão menor e com menor faixa de distribuição de tamanhos, enquanto que para o lítio houve uma menor perda de massa. A mescla de pós permitiu obter maiores valores de densidade a verde, reduzir a perda de massa e obter uma cerâmica mais densa. A adição de,...
This work aims at getting the relaxor ceramic PMN with temperature of maximum dielectric constant close to room temperature, high dielectric constant and low dielectric loss values. The influence of the potassium and lithium additives during powder synthesis and processing of the PMN ceramic constitutes a great contribution to the research of this material type. The PMN powders were synthesized by using the columbite route associated to the lead co-precipitation method. The columbite phase formation was verified by XRD. The structure refinement, calculus of mean crystallite size and lattice microstrain were performed by using the Rietveld method. Furthermore, the samples were characterized by TG/DTA, BET and SEM. Differing from lithium, potassium increases the temperature of MgNb2O6 phase formation, however it does not hinder obtaining the monophasic precursor until 2mol% of additives. For columbite powders, burned at 900ºC during 2 hours, additive presence attenuates the lattice microstrain and increases the mean crystallite size and, consequently, the secondary particle formation occurs. The values of mean size crystallite for lithium doped-PMN samples burned at 800ºC during 2 hours are bigger than potassium ones. In this condition, the lithium doping causes particles growth and powder agglomeration. In sintering, the potassium doped-PMN samples showed smaller grain size and short range of size distribution, while the lithium doped ones showed lesser weight loss. The powder mixture allowed obtaining greater green density values, decreasing weight loss and getting a denser ceramic. Potassium addition reduces Km and Tm values, while the lithium addition, increases these values if compared to PMN. The utilization of LiNbO3 seeds reduces the weight loss and helps the ceramic densification. The seeded sample showed a diffuse phase transition more...(Complete abstract, click electronic access below)
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Randall, C. A. "A transmission electron microscopy study of normal and relaxor perovskite ferroelectric materials." Thesis, University of Essex, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376749.
Full text
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Paxton, Benjamin John. "Development of phonon-polarization THz spectroscopy, and the investigation of relaxor ferroelectrics." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/36264.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2006.Vita.
Includes bibliographical references (p. 155-162).
This thesis develops phonon-polariton based THz spectroscopy and uses this technique to make the first THz frequency dielectric measurements of a relaxor ferroelectric crystal, in particular KTao0.982Nb0.018O3 (KTN 1.8). THz spectroscopy has emerged as an important probe for a wide variety of systems with the development of pulsed THz radiation sources and time-domain detection methods. Four factors motivate the use of phonon-polaritons generated in an ionic crystal (typically LiNbO3 or LiTaO3) via impulsive stimulated Raman scattering as a THz source for spectroscopy: (1) the versatility of phonon-polariton waveform shaping and detection, (2) the ability to use the ionic crystal as a compact, integrated spectroscopic platform, (3) the high THz refractive index of the host material facilitates coupling of THz radiation into high-dielectric samples, and (4) the potential to generate large amplitude polariton fields for nonlinear THz spectroscopy. Here we demonstrate both reflection and transmission implementations of THz spectrometers based on grating interferometric measurement of the phase and amplitude of a phonon-polariton waveform before and after interaction with a sample.
(cont.) A simple implementation of free space THz spectroscopy with conventional detection is also performed as a comparison to the polariton spectroscopy measurements. For the investigation of high-dielectric materials, both reflection and transmission polariton spectroscopy offer clear advantages over free space methods. Polariton spectroscopy is used to measure the refractive index of KTN 1.8 in the -50-250 GHz range from 4-300 K as the index varies between -10 and 35. At low temperatures, the Nb ions in our sample induce dynamically fluctuating polar nano-regions (PNRs) that dominate the dielectric response at low at low frequencies (< 10-7 Hz). Our results differed from low frequency measurements in two ways: a significantly smaller, but still ionic, dielectric response and Curie-Weiss soft mode behavior. Together with ISRS transient grating measurements of the KTN soft mode in the low temperature disordered state, we attribute this behavior to soft mode mediated fast Nb intersite hopping separated from slower PNR dynamics.
by Benjamin John Paxton.
Ph.D.
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Al-Zein, Ali. "Order and Disorder of Relaxor and Ferroelectric Materials : structural and Vibrational Studies." Thesis, Montpellier 2, 2010. http://www.theses.fr/2010MON20078/document.
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Parmi les matériaux piézo-électriques, les pérovskites ferroélectriques à base de plomb sont connus pour avoir les meilleurs coefficients piézo-électriques et couplage électromécanique. Ils sont largement utilisés dans diverses applications industrielles et technologiques. Les "ferroélectrique relaxeurs" appartiennent à cette famille. Leur structure est caractérisée par la présence de nanorégions polaires orientées de façon aléatoire. Dans cette thèse, nous nous sommes intéressés à l'étude des propriétés structurales et dynamiques de matériaux ferroélectriques et relaxeurs tels que PbTiO3, PbZr0.52Ti0.48O3, PbMg1/3Nb2/3O3 (PMN), PbZn1/3Nb2/3O3, et PbMg1/3Ta2/3O3 (PMT). La structure à longue et courte portée a été étudiée par diffraction de neutrons et spectroscopie d'absorption des rayons X (XAFS), alors que la spectroscopie hyper-Raman (HR) est utilisée pour sonder les vibrations. L'analyse de la structure locale de matériaux pérovskites complexes AB'B''O3 montre que la pression diminue le désordre statique des gros cations occupant le site B, tandis que le champ électrique appliqué a un effet opposé. Cette distortion induite sous champ pourrait être à l'origine des forts coefficient piézoélectrique dans ces matériaux. La diffusion HR dans PMN et PMT a permis d'observer pour la première fois le "mode mou" responsable de la dépendance en température de la constante diélectrique. L'analyse des règles de sélection et la description en modes propres des vibrations actives en HR, permet de rendre compte de l'implication de chaque atome dans le comportement structural en température des ferroélectriques relaxeursAmong piezoelectric materials, lead-based ferroelectric perovskites are known to have the largest piezoelectric coefficients and electromechanical coupling. They are widely used in dfferent industrial and technological applications. The so-called "relaxors" belong to this family. Their structure is characterized by the presence of randomly oriented polar nanoregions. In this thesis, we are interested in studying the structural and dynamical properties of prototypical ferroelectric materials and relaxors such as PbTiO3, PbZr0.52Ti0.48O3, PbMg1/3Nb2/3O3 (PMN), PbZn1/3Nb2/3O3, and PbMg1/3Ta2/3O3 (PMT). The long and short range structure has been investigated by neutron diffraction and X-ray absorption fine structure (XAFS), while hyper-Raman scattering (HRS) is used to probe the vibrations. The local structure analysis of complex perovskite materials AB'B''O3 shows that pressure reduces the static disorder of the large cation occupying the B-site, while an applied electric field has an opposite effect. This field-induced distortion might relate to the large piezoelectric coefficient in such materials. HRS in PMN and PMT allows the first observation of the "primary" soft mode responsible for the temperature dependence of the dielectric constant. The selection rule analysis reveals the nature of the HRS active vibrational bands and enables us to get insights about the involvement of each atom in the structural modifications upon temperature
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Cavalheiro, Alberto Adriano. "Influência dos dopantes potássio e lítio na cerâmica relaxora niobato de chumbo e magnésio (PMN) /." Araraquara : [s.n.], 2002. http://hdl.handle.net/11449/102590.
Full textAbstract:
Resumo: Este trabalho se focaliza na obtenção da cerâmica relaxora PMN com temperatura de máxima constante dielétrica se situando próximo à temperatura ambiente, alta constante dielétrica e valores de perda dielétrica baixos. A influência dos dopantes potássio e lítio durante a síntese dos pós e o processamento da cerâmica PMN constitui uma grande contribuição para a pesquisa deste tipo de material. Os pós de PMN foram sintetizados utilizando a rota da columbita associada ao método de coprecipitação de chumbo. O monitoramento da formação da fase columbita foi acompanhado por DRX. O refinamento de estrutura, o cálculo do tamanho médio de cristalito e a microdeformação de rede foram executadas utilizando o método de Rietveld. Além disso, as amostras foram caracterizadas por TG/DTA, BET e MEV. Diferentemente do lítio, o potássio provoca a elevação da temperatura de formação da fase MgNb2O6 (MN), mas isto não interfere na obtenção do precursor monofásico até a concentração de 2,0%mol de dopante. Para pós de MN calcinados a 900ºC por 2 horas, a presença dos dopantes atenuam a microdeformação de rede e aumentam o tamanho médio de cristalito e, conseqüentemente ocorre a formação de partículas secundárias. Os valores de tamanho médio de cristalito das amostras de PMN dopadas com lítio, calcinadas a 800ºC por 2 horas, são maiores do que para as amostras dopadas com potássio. Nesta condição, a adição de lítio também acarreta crescimento de partículas e aglomeração dos pós. Durante a sinterização, as amostras dopadas com potássio apresentaram tamanho de grão menor e com menor faixa de distribuição de tamanhos, enquanto que para o lítio houve uma menor perda de massa. A mescla de pós permitiu obter maiores valores de densidade a verde, reduzir a perda de massa e obter uma cerâmica mais densa. A adição de,...(Resumo completo, clicar acesso eletrônico abaixo)Abstract: This work aims at getting the relaxor ceramic PMN with temperature of maximum dielectric constant close to room temperature, high dielectric constant and low dielectric loss values. The influence of the potassium and lithium additives during powder synthesis and processing of the PMN ceramic constitutes a great contribution to the research of this material type. The PMN powders were synthesized by using the columbite route associated to the lead co-precipitation method. The columbite phase formation was verified by XRD. The structure refinement, calculus of mean crystallite size and lattice microstrain were performed by using the Rietveld method. Furthermore, the samples were characterized by TG/DTA, BET and SEM. Differing from lithium, potassium increases the temperature of MgNb2O6 phase formation, however it does not hinder obtaining the monophasic precursor until 2mol% of additives. For columbite powders, burned at 900ºC during 2 hours, additive presence attenuates the lattice microstrain and increases the mean crystallite size and, consequently, the secondary particle formation occurs. The values of mean size crystallite for lithium doped-PMN samples burned at 800ºC during 2 hours are bigger than potassium ones. In this condition, the lithium doping causes particles growth and powder agglomeration. In sintering, the potassium doped-PMN samples showed smaller grain size and short range of size distribution, while the lithium doped ones showed lesser weight loss. The powder mixture allowed obtaining greater green density values, decreasing weight loss and getting a denser ceramic. Potassium addition reduces Km and Tm values, while the lithium addition, increases these values if compared to PMN. The utilization of LiNbO3 seeds reduces the weight loss and helps the ceramic densification. The seeded sample showed a diffuse phase transition more...(Complete abstract, click electronic access below)
Orientador: Maria Aparecida Zaghete
Coorientador: Carlos de Oliveira Paiva Santos
Banca: Edson Roberto Leite
Banca: Ivair Aparecido dos Santos
Banca: Ruth Herta Goldschimidt Aliaga Kiminami
Banca: Wanda Cecília Las
Doutor
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Brown, James Emery. "Advances in electrical energy storage using core-shell structures and relaxor-ferroelectric materials." Diss., Kansas State University, 2018. http://hdl.handle.net/2097/38779.
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Doctor of PhilosophyDepartment of Chemistry
Jun Li
Electrical energy storage (EES) is crucial in todays’ society owing to the advances in electric cars, microelectronics, portable electronics and grid storage backup for renewable energy utilization. Lithium ion batteries (LIBs) have dominated the EES market owing to their wide use in portable electronics. Despite the success, low specific capacity and low power rates still need to be addressed to meet the increasing demands. Particularly, the low specific capacity of cathode materials is currently limiting the energy storage capability of LIBs. Vanadium pentoxide (V₂O₅) has been an emerging cathode material owing to its low cost, high electrode potential in lithium-extracted state (up to 4.0 V), and high specific capacities of 294 mAh g⁻¹ (for a 2 Li⁺/V₂O₅ insertion process) and 441 mAh g⁻¹ (for a 3 Li⁺/V₂O₅ insertion process). However, the low electrical conductivities and slow Li⁺ ion diffusion still limit the power rate of V₂O₅. To enhance the power-rate capability we construct two core-shell structures that can achieve stable 2 and 3 Li⁺ insertion at high rates. In the first approach, uniform coaxial V₂O₅ shells are coated onto electrospun carbon nanofiber (CNF) cores via pulsed electrodeposition. The materials analyses confirm that the V₂O₅ shell after 4 hours of thermal annealing at 300 °C is a partially hydrated amorphous structure. SEM and TEM images indicate that the uniform 30 to 50 nm thick V₂O₅ shell forms an intimate interface with the CNF core. Lithium insertion capacities up to 291 and 429 mAh g⁻¹ are achieved in the voltage ranges of 4.0 – 2.0 V and 4.0 – 1.5 V, respectively, which are in good agreement with the theoretical values for 2 and 3 Li⁺/V₂O₅ insertion. Moreover, after 100 cycles, remarkable retention rates of 97% and 70% are obtained for 2 and 3 Li⁺/V₂O₅ insertion, respectively. In the second approach, we implement a three-dimensional (3D) core-shell structure consisting of coaxial V₂O₅ shells sputter-coated on vertically aligned carbon nanofiber (VACNF) cores. The hydrated amorphous microporous structure in the “as-deposited” V₂O₅ shells and the particulated nano-crystalline V₂O₅ structure formed by thermal annealing are compared. The former provides remarkably high capacity of 360 and 547 mAh g⁻¹ in the voltage range of 4.0 – 2.0 V and 4.0 – 1.5 V, respectively, far exceeding the theoretical values for 2 and 3 Li⁺/V₂O₅ insertion, respectively. After 100 cycles of 3 Li⁺/V₂O₅ insertion/extraction at 0.20 A g⁻¹ (~ C/3), ~ 84% of the initial capacity is retained. After thermal annealing, the core-shell structure presents a capacity of 294 and 390 mAh g⁻¹, matching well with the theoretical values for 2 and 3 Li⁺/V₂O₅ insertion. The annealed sample shows further improved stability, with remarkable capacity retention of ~100% and ~88% for 2 and 3 Li⁺/V₂O₅ insertion/extraction. However, due to the high cost of Li. alternative approaches are currently being pursued for large scale production. Sodium ion batteries (SIB) have been at the forefront of this endeavor. Here we investigate the sodium insertion in the hydrate amorphous V₂O₅ using the VACNF core-shell structure. Electrochemical characterization was carried out in the potential ranges of 3.5 – 1.0, 4.0 – 1.5, and 4.0 – 1.0 (vs Na/Na⁺). An insertion capacity of 196 mAh g-1 is achieved in the potential range of 3.5 – 1.0 V (vs Na/Na⁺) at a rate of 250 mA g⁻¹. When the potential window is shifted upwards to 4.0 – 1.5 V (vs Na/Na⁺) an insertion capacity of 145 mAh g⁻¹ is achieved. Moreover, a coulombic efficiency of ~98% is attained at a rate of 1500 mA g⁻¹. To enhance the energy density of the VACNF-V₂O₅ core-shell structures, the potential window is expanded to 4.0 – 1.0 V (vs Na/Na⁺) which achieved an initial insertion capacity of 277 mAh g⁻¹. The results demonstrate that amorphous V₂O₅ could serve as a cathode material in future SIBs.
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Ma, Yangbin [Verfasser], Baixiang [Akademischer Betreuer] Xu, Karsten [Akademischer Betreuer] Albe, and Peter [Akademischer Betreuer] Entel. "Electrocaloric Effect of Ferroelectrics and Relaxors / Yangbin Ma ; Baixiang Xu, Karsten Albe, Peter Entel." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2018. http://d-nb.info/1162275200/34.
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Ma, Yang-Bin [Verfasser], Baixiang [Akademischer Betreuer] Xu, Karsten [Akademischer Betreuer] Albe, and Peter [Akademischer Betreuer] Entel. "Electrocaloric Effect of Ferroelectrics and Relaxors / Yangbin Ma ; Baixiang Xu, Karsten Albe, Peter Entel." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2018. http://d-nb.info/1162275200/34.
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Kim, Young-Il. "Syntheses, crystal structures, and dielectric property of oxynitride perovskites." Connect to resource, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1124291783.
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Thesis (Ph. D.)--Ohio State University, 2005.Title from first page of PDF file. Document formatted into pages; contains xvi, 172 p.; also includes graphics (some col.). Includes bibliographical references (p. 160-172). Available online via OhioLINK's ETD Center
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Namboodri, Chettoor G. "Experimental investigation and modeling of the electrostrictive relaxor ferroelectric lead magnesium niobate-lead titinate." Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-07212009-040304/.
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Ndlovu, (Mamabolo) Thabisile Mavis. "The effects of hair relaxer treatment on the amino acid profile and surface characteristics of South African Negroid hair." Thesis, University of Limpopo (Medunsa Campus), 2011. http://hdl.handle.net/10386/669.
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Thesis (MSc (Chemistry)) -- University of Limpopo, 2011.Surveys indicate that most South African origin women want long and straight hair (Mamabolo and Summers, 2006). Such women will therefore use a relaxer to straighten their hair. Many such preparations cause damage to the hair and scalp; hence identification of an effective and mild relaxer would be advantageous. This dissertation investigates South African origin hair structure and goes on to describe the effects of relaxers on South African origin hair. This work also analyses the effects of the lye and no-lye relaxers separately. The work was divided into two sections. The first section was the clinical study where two types of relaxers (‘lye’, a sodium hydroxide base relaxer and ‘no-lye’, a guanidine hydroxide base relaxer) were applied on the new outgrowth representing natural hair in a half-head study design of five South African origin female volunteers. Subjective (subject self-assessment) and objective (Researcher assessment) hair assessments were performed. The second section was the analysis of the hair samples by Reversed-Phase High Performance Liquid Chromatography (HPLC) using the Pico Tag as well as Electron Microscopy. There was no erythema detected in the clinical study on the scalp of any of the subjects post-application. Both the researcher and the subjects assessed the performance of the no-lye relaxer to be better than the lye relaxer in terms of straightness. The researcher also assessed the performance of the no-lye relaxer to be better than the lye relaxer in terms of softness, shininess, volume and dryness. The performance of the two types of relaxers was assessed to be the same by both the researcher and the subjects in terms of length and damage. There was a statistically significant (p< 0.1) decrease in the amount (g/100 g hair) of cystine after treatment compared to before treatment with both the lye relaxer (median [range]) (7.8 [2.5-9.9] vs. 9.1 [6.7-11.9]; p= 0.086) and the no-lye relaxer (4.0 [2.9-4.8] vs. 9.1 [6.7-11.9]; p= 0.005); this decrease was significantly greater (p= 0.086) for the no-lye relaxer. There was also a statistically significant decrease in the amount of lysine after treatment compared to before treatment with both the lye relaxer (2.0 [1.5-2.3] vs. 2.1 [2.0-2.6]; p= 0.082) and the no-lye relaxer (2.0 [1.5-2.2]; p= 0.036); this decrease was not significantly different (p= 0.920) for the two types of relaxer. No significant differences were found in the levels of the remaining 15 amino acids analysed. For all the subjects no physical evidence of hair damage was observable from the scanning electron microscopy images of the hair shafts and the cuticles. The longer wash-off time confirmed the claimed relative safety of ‘no-lye’ relaxers. The no-lye relaxer performed better overall than the lye relaxer in terms of the hair quality parameters assessed. A decrease in cystine levels is consistent with better performance in terms of hair straightness. The results from electron microscopy were not conclusive.
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Wang, Shuai [Verfasser], Bai-Xiang [Akademischer Betreuer] Xu, and Wolfgang [Akademischer Betreuer] Kleemann. "Phase-Field Modeling of Relaxor Ferroelectrics and Related Composites / Shuai Wang ; Bai-Xiang Xu, Wolfgang Kleemann." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2019. http://d-nb.info/1177241668/34.
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Qiu, Zhen. "Development of MRI-compatible transducer array for focused ultrasound surgery : the use of relaxor-based piezocrystals." Thesis, University of Dundee, 2014. https://discovery.dundee.ac.uk/en/studentTheses/572decc1-6a5b-420a-948d-e8f05740fcd5.
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Focused ultrasound surgery (FUS) is considered as a promising approach for treating cancer and other conditions and is gaining increasing interest. However, the limited availability of experimental ultrasound array sources and multichannel electronics able to drive them hinder the research into FUS system configurations for patient conditions such as breast cancer. The work in this dissertation explored the development of ultrasound arrays for MRI guided FUS, from the point of view of the potential piezoelectric material of choice. Two materials are of particular interests in this work: Binary (x)Pb(Mg1/3Nb2/3) O3 - (1-x)PbTiO3 (PMN-PT) piezocrystal, and newly specialized FUS material, PZ54 ceramic. A characterization methodology was developed to fully characterize the materials of choice, under ambient and extreme conditions relevant to FUS applications. Practicalities of adopting these materials into FUS were studied by using the characterized materials in designing and fabricating FUS arrays. A spherical, faceted array geometry inspired by the geodesic dome structure was proposed and implemented for the first time. Four bespoke devices, each with 96 individual elements, were implemented using PZ26 ceramic, PZ26 composite, PZ54 composite and PMN-PT composite materials, respectively for comparison. The arrays were connected to commercial electronics afterwards, to explore a prototyping route for connecting FUS devices and modular driving systems. It is concluded that PMN-PT piezocrystal and PZ54 ceramic material can offer excellent performance over conventional piezoelectric ceramics, although PMN-PT piezocrystal is sensitive to extreme conditions. The usable range of PMN-PT is suggested to be limited to 60°C in temperature and 10 MPa in pressure. However, PMN-PT piezocrystal could still be a potential alternative to conventional ceramics in FUS application if assisted with sufficient cooling circulation and bias field. The geodesic array geometry is also concluded to be able to achieve good focusing of ultrasound beam. With optimized phase control through multi-channel electronics, the focusing was improved with focusing gain up to about 30; the steering range of focus was explored within a volume of 5 x 5 x 10 mm3 beyond the array’s geometric focus, side lobes were limited to below the level of -9 dB in acoustic intensity. Larger numbers of individual controllable elements and alternative array designs will be explored in future to investigate application such as breast cancer treatment and potential pre-clinical trials.
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Freire, Rafael Luiz Heleno. "Síntese e propriedades físicas de filmes ferroelétricos do sistema PLZT /." Ilha Solteira : [s.n.], 2012. http://hdl.handle.net/11449/91956.
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Orientador: Eudes Borges de AraújoBanca: Rafael Zadorosny
Banca: Jesiel Freitas Carvalho
Resumo: O titanato zirconato de chumbo dopado com lantânio, dado convencionalmente pela fórmula estequiométrica Pb1− x Lax ( Zry ; Ti1− y ) 1− x / 4 O3 , com x = 0,09 e y = 0,65, também conhecido como PLZT 9/65/35, é um importante sistema ferroelétrico relaxor devido as suas propriedades dielétricas, elétricas e eletroóticas. Sendo um ferroelétrico, exibe, também, propriedades tais como piezo e piroeletricidade, dependendo apenas das proporções em que são preparados. Logo, esse sistema é bastante interessante para uma gama de aplicações tecnológicas. Na forma de filmes finos, a composição PLZT 9/65/35 tem sido amplamente estudada e preparada pelos mais diversos métodos. Neste trabalho propõe-se a síntese de filmes finos ferroelétricos da composição PLZT 9/65/35 pelo método dos precursores óxidos, a fim de se compreender a dinâmica dos processos de cristalização e, também, avaliar suas propriedades físicas, como permissividade elétrica e histerese ferroelétrica. A intenção, assim, é colaborar com as informações presentes na literatura sobre as propriedades de filmes finos de PLZT 9/65/35
Abstract: The lead zirconate titanate doped with lanthanum, conventionally given by stoichiometric formula Pb1− x Lax ( Zry ; Ti1− y ) 1− x / 4 O3 , with x=0,09 and y=0,65, also known as PLZT 9/65/35, is an important relaxor ferroelectric system due to its dielectric, electrical and electrooptical properties. Being a ferroelectric material exhibits also properties such as piezo- and piroelectricity, depending upon the extent to which they are prepared. Therefore, this system is very interesting for a range of technological applications. In the thin films format, the composition PLZT 9/65/35 has been widely studied and prepared by several methods. In this project it is proposed the synthesis of thin films of such material by the oxide precursor method in order to understand the dynamics of crystallization process and also to evaluate their physical properties like electrical permittivity and ferroelectric hysteresis. The intention, thus, is collaborate with the information presented in the literature about the properties of PLZT 9/65/35 thin films
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Tong, Sheng. "Dielectric and Ferroelectric Properties of Lead Lanthanum Zirconate Titanate Thin Films for Capacitive Energy Storage." University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1352993943.
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Butcher, Steven John. "Relaxor ferroelectricity in (Pbâ†xBaâ†1â†-â†x)(Mgâ†1â†/â†3Nbâ†2â†/â†3)Oâ†3 ceramics." Thesis, University of Leeds, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329474.
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Mesquita, Alexandre. "Síntese e caracterização estrutural e dielétrica de compostos ferroelétricos \'PB IND.1-X\'\'R IND.X\'\'ZR IND.0,40\'\'TI IND.0,60\'\'O IND.3\' (R = La, Ba)." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/88/88131/tde-19042011-172117/.
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O titanato e zirconato de chumbo \'PB\'(\'ZR\'1-y\'TI\'y)\'O IND.3\' é um material ferroelétrico de estrutura perovskita que tem sido aplicado como transdutores, amplificadores, sensores piezoelétricos, piroelétricos e memórias ferroelétricas. É bem estabelecido que a incorporação de íons de \'LA POT.3+\' ou \'BA POT.2+\' nos sítios ocupados pelo \'PB\' no sistema \'PB\'(\'ZR\'1-y\'TI\'y)\'O\' (PZT), formando os sistemas \'PB\'1-x\'LA\'x\'ZR\'1-y\'TI\'y\'O IND.3\' (PLZT) e \'PB\'1-x\'BA\'x\'ZR\'1-y\'TI\'y\'O IND.3\' (PBZT), provoca mudanças significativas nas suas propriedades. No entanto, poucos trabalhos tem sido dedicados a esses sistemas contendo altas concentrações de \'TI\', principalmente no que se refere à estrutura desses materiais. Assim, este trabalho teve por objetivo analisar as propriedades estruturais e suas correlações com as propriedades dielétricas dos sistemas \'PB\'1-x\'LA\'x\'ZR\'0,40\'TI\'0,60\'O IND.3\' (PLZT100x) e \'PB\'1-x\'BA\'x\'ZR\'0,40\'TI\'0,60\'O IND.3\' (PBZT100x) em função da composição e da temperatura. Foram preparadas amostras cerâmicas por meio de sinterização convencional com x variando entre 0,05 e 0,21 para o sistema PLZT e entre 0,10 e 0,50 para o sistema PBZT. Em relação à estrutura a longa distância, medidas de difração de raios X mostraram uma diminuição no grau de tetragonalidade com o aumento da concentração dos cátions substituintes, que foi atribuída à formação de vacâncias no sítio A (caso do \'LA\') e diferença entre o raio iônico (caso do \'BA\'). Estas alterações estruturais em função da composição foram também responsáveis pelo aumento do grau de difusidade das curvas de permissividade dielétrica e pela observação de um estado ferroelétrico relaxor nas amostras contendo altas concentrações de \'LA\' e \'BA\'. Em relação à estrutural local, os resultados obtidos através da técnica de espectroscopia de absorção de raios X (XAS) nas bordas \'K\' do \'TI\' e LIII do \'PB\' mostraram que a incorporação de átomos de \'LA\' ou \'BA\' à estrutura do PZT leva a uma redução no deslocamento do átomo de \'TI\' em relação ao centro do octaedro \'TI\'O IND.6\' e mudanças na ordem local do átomo de \'PB\'. No que tange as composições contendo 21% at. de \'LA\' e 50% at. de \'BA\', diferentemente dos resultados de DRX que mostraram uma simetria cúbica, a técnica de XAS mostrou uma simetria local tetragonal. Em bom acordo com os resultados obtidos pela técnica de espectroscopia Raman, espectros EXAFS medidos em altas temperaturas mostraram também que a estrutura local não é compatível com uma estrutura de simetria cúbica. Espectros XANES medidos na borda \'K\' do oxigênio revelaram uma redução no grau de hibridização entre os estados 2p do \'O\' com 6sp do \'PB\' à medida que a concentração de \'LA\' ou \'BA\' aumenta, que estaria relacionada com o surgimento de comportamento relaxor. Amostras cerâmicas densas nanoestruturadas de composição PZT, PLZT11 e PBZT10 foram preparadas pelo método de spark plasma sintering (SPS) a fim de analisar a influência do tamanho de grão. Foi verificado que as amostras sinterizadas por SPS apresentam tamanho de grão em torno de 60 nm. A caracterização dielétrica destas amostras mostra que a redução do tamanho de grão causa uma redução no valor de máximo da permissividade dielétrica e características difusas da permissividade em função da temperatura devido ao aumento das regiões de contorno de grão.Lead titanate zirconate (\'PB\'(\'ZR\'1-x\'TI\'x)\'O IND.3\') are ferroelectric materials with perovskite structure which has been used as transducers, capacitors, piezoelectric and pyroelectric sensors and ferroelectric memories. The substitution of \'PB POT.+2\' ions by \'LA POT.+3\' or \'BA POT.+2\' ions in the \'PB\'(\'ZR\'1-x\'TI\'x)\'O IND.3\' (PZT) system, which leads to the formation of the \'PB\'1-x\'LA\'x\'ZR\'1-y\'TI\'y\'O IND.3\' (PLZT) and the \'PB\'1-x\'BA\'x\'ZR\'1-y\'TI\'y\'O IND.3\' (PBZT) systems, induces several changes in the electric and structural properties of these materials. However, PLZT or PBZT systems based on \'TI\'-rich compositions have not been thoroughly investigated and the literature contains few reports concerning their structure. Thus, the main objectives of this doctoral thesis were the synthesis and structural characterization of \'PB\'1-x\'R\'x\'ZR\'0.40\'TI\'0.60\'O IND.3\' ferroelectric ceramic samples, with R = \'BA\' and \'LA\' and x between 0.00 to 0.50 (PLZT100x and PBZT100x). The characterization with X-ray diffraction technique of these samples showed a decrease of the tetragonality degree with increase of the doping cation concentration, which was related to the appearance of defects caused by the incorporation of \'LA\' or \'BA\' cations. These structural modifications were also responsible by the increase of the diffuseness at the dielectric permittivity and a relaxor behavior as a function of the \'LA\' or \'BA\' concentration. Concerning the local structure, XANES spectra in the absorption edge of various elements in PLZT and PBZT samples were performed. In the cases of \'TI\' \'K\'-edge absorption, the doping of \'LA\' and \'BA\' atoms in the PZT structure leads to a reduction of the displacement of \'TI\' atom in the center of the \'TI\'O IND.6\' octahedron. However, even when the crystal structure is cubic, a local octahedron distortion remains. EXAFS measurements in \'PB\' LIII-edge and \'ZR\' \'K\'-edge were performed and also indicate that local structure around lead or zirconium atoms is also affected by the introduction of \'LA\' and \'BA\' atoms in the PZT structure. In addition, XANES spectra measured at \'O\' \'K\'-edge revealed a reduction in the hybridization degree between \'O\' 2p and \'PB\' 6sp states with the addition of \'LA\' or \'BA\' atoms to the structure of PZT. It has been shown that hybridization between these states is essential to ferroelectricity and this reduction would be related to the relaxor behavior. PLZT and PBZT systems were also studied depending on the size of particle size in a nanometer scale. Thus samples PZT, PLZT11 and PBZT10 compositions were prepared using the synthesis method of precursor polymers and the process of sintering by spark plasma. A pronounced decrease in the values of maximum permittivity was observed and the dielectric curve as a function of the temperature exhibits a diffuse behavior. This size-induced diffuse phase transition and the reduction of the permittivity magnitude could be related to the differences between the core grain and the grain boundaries.
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Milton, Flávio Paulo. "Ferroelétricos relaxores canônicos: um estudo a partir do efeito eletro-óptico em função da temperatura." Universidade Federal de São Carlos, 2013. https://repositorio.ufscar.br/handle/ufscar/4985.
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This study revisits the lanthanum-modified lead zirconate titanate ferroelectric relaxor system (PLZT) by investigating its electro-optical properties, particularly the variation of birefringence induced by electrical field, n(E). The thermal evolution of n(E), obtained by the Kerr (quadratic) and Pockels (linear) electro-optical effects, was considered in the verification of possible critical temperatures predicted for the transitions between the paraelectric (PE), ergodic ferroelectric relaxor (EFR), non-ergodic ferroelectric relaxor (NEFR), and normal ferroelectric (FE) states. Such temperatures identify the regions that separate different correlation states (static and dynamic) from the polar nano-regions (PNR) present in these materials. This work made use of ceramics La/Zr/Ti = 9/65/35, which are located on the tricritical point of the PZLT phase diagram. The effect of doping with 1% weight of rare-earth oxides (Nd, Ho, Er, Tm e Yb) upon the relaxor behaviour was also investigated. The undoped material was used as a reference system in the elaboration of a protocol for data collection and treatment, which included the results of ferroelectric, dielectric and pyroelectric measurements. The n(E) results obtained for the quadratic response (Kerr effect) as a function of temperature were suitable for determining the freezing temperature (Tf) associated to the FE-FRE transition or to the FRE-FRNE transition, as well as the temperature associated to the maximum electrical permittivity (Tε′m), and the Burns temperature (TB) associated to the FRE-PE transition. Conversely, the dependence of n(E) to linear response (Pockels effect) as a function of temperature proved sensitive for determining the characteristic temperature T*, which indicates the initial temperature for a correlated state of short and mid-range NRP reach during cooling of the material. All of these characteristic temperatures could be determined for the doped PLZT system as well, and the same behaviours were observed for the Kerr and Pockels electro-optical responses. It is worth noting that this is the first time the n(E) linear effect response is applied to the analysis of this system. However, the transition intervals between polar and non-polar states suffered changes according to rules associated to the difference between the ionic radii of rare-earth and the cation that had been replaced in the crystal structure. Although the ferroelectric, electric, dielectric, pyroelectric, and electro-optical properties of the PLZT system were clearly affected by doping, no significant changes in the relaxor behaviour could be observed.
Este trabalho revisita o sistema ferroelétrico relaxor titanato zirconato de chumbo modificado com lantânio (PLZT) a partir de investigações de suas propriedades eletro-ópticas, particularmente da variação da birrefringência induzida por campo elétrico, n(E). Foi considerada a evolução térmica de n(E), obtida pelos efeitos eletro-ópticos Kerr (quadrático) e Pockels (linear), para a determinação (ou validação) de possíveis temperaturas críticas, características de transições entre os estados paraelétrico (PE), ferroelétrico relaxor ergódico (FRE), ferroelétrico relaxor não-ergódico (FRNE) e ferroelétrico normal (FE), previstas para sistemas ferroelétricos relaxores. Tais temperaturas identificam as regiões que separam diferentes estados de correlação (estática e dinâmica) das nano-regiões polares (NRP) presentes nesses materiais. Para o estudo, foram utilizadas cerâmicas da composição La/Zr/Ti = 9/65/35, nomeado PLZT, que se localiza no ponto tricrítico do diagrama de fases. O efeito da dopagem neste sistema, com 1% em peso de óxidos de elementos terras-raras (Nd, Ho, Er, Tm e Yb) sobre o comportamento relaxor, também foi discutido. Como sistema de referência, foram utilizados protocolos de aquisição e tratamento de dados, que incluíram também resultados de medidas ferroelétricas, dielétricas e piroelétricas. Verificou-se que os resultados de n(E) para a resposta quadrática (efeito Kerr), em função da temperatura, permitem a determinação da temperatura de freezing (Tf), associada ora à transição FE-FRE e ora à FRE-FRNE; da temperatura associada àquela de máximo da permissividade elétrica (Tε′m); e da temperatura de Burns (TB), associada à transição FRE-PE. Já a dependência de n(E), para a resposta linear (efeito Pockels), com a temperatura, permite a determinação da temperatura característica T*, indicadora do ponto inicial de um estado correlacionado de curto e médio alcance das NRP, durante o resfriamento do material. Trata-se da primeira vez em que a resposta n(E) do efeito linear é aplicada à análise de sistemas como esse. Todas as temperaturas características puderam ser determinadas no sistema dopado, sendo observadas as mesmas peculiaridades para as respostas eletro-ópticas Kerr e Pockels. Contudo, os intervalos para as transições entre os estados polar e não-polar deslocaram-se, seguindo regras associadas à diferença entre o raio iônico do terra-rara em relação ao do cátion substituído na rede cristalina. Embora a dopagem tenha alterado as propriedades ferroelétricas, elétricas, dielétricas, piroelétricas e eletro-ópticas do sistema PLZT, em geral não foram observadas mudanças no comportamento relaxor.
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Dittmer, Robert [Verfasser], Jürgen [Akademischer Betreuer] Rödel, and Karsten [Akademischer Betreuer] Albe. "Lead-Free Piezoceramics – Ergodic and Nonergodic Relaxor Ferroelectrics Based on Bismuth Sodium Titanate / Robert Dittmer. Betreuer: Jürgen Rödel ; Karsten Albe." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2013. http://d-nb.info/1107771757/34.
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Zhao, Xiaohui. "Development of long range cation order and its impact on dielectric properties in Pb(Mg₁/₃Nb₂/₃)O₃ based relaxor ferroelectrics." [Ames, Iowa : Iowa State University], 2008.
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