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1
Sakabe, Yukio. "Calcium-doped barium titanate ceramics for nickel electrode multilayer capacitors." 京都大学 (Kyoto University), 2003. http://hdl.handle.net/2433/149473.
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Kotlyarchuk, A., A. Ragulya, V. Klymenko, N. Dubovitskaya, T. Lobunets, and S. Shatskikh. "Doped Barium Titanate at Intermediate Stages of Synthesis of ВТО." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35475.
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This paper presents the results of synthesis and characterization of calcium 0doped nanocrystalline
barium titanate powder with different concentration of doped elements ((Ba1-xCax) TiO3, were x 0; 0.02;
0.06; 0.1; 0.16; 0.2), produced by oxalate route. Calcium additives were added on the surface the samples of
semidecomposed barium titanil oxalate. For synthesis were used simultaneously decomposition of unstable
barium, titanium compositions and calcium salts. The semidecomposed barium titanil oxalate and doped
barium titanate characterization carried out by specific surface area measurements, TEM, X-Ray. It is experimentally
shown that Са2+ introduction reduces lattice parameter for samples that related with replacement
of barium by calcium. Solubility of calcium in barium titanate nanopowders increase from
10 at % up to 16 at %. The second phase appears at 20 at %.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35475
3
Shu, Chang. "Investigation of the structural and functional properties of lead-free barium calcium zirconate titanate piezoceramics." Thesis, University of Birmingham, 2018. http://etheses.bham.ac.uk//id/eprint/8148/.
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There is an urgent desire to move from lead-based piezoelectric materials to lead-free alternatives. One of the most promising lead-free materials has been reported to be zBao.7oCao.3oTi0J-(1-z) BaZro.2oTio.soOJ (abbreviated as zBCT-(1-z)BZT) system, which has comparable piezoelectric performance to lead-based materials. However, there is a lack of systematic research to investigate the effects of fabrication on the structural and functional properties of this zBCT -(1-z)BZT system. In this work, the end member Bai-xCaxTiOJ (x=0-0.30) and BaZryTii-y03 (ji=0-0.30) systems have been investigated. The phase transition diagrams of the two systems have been successfully established by measuring temperature dependent Raman spectroscopy and functional properties. The optimized fabrication procedure for forming single phased Bao.7oCao.3oTi0J and BaZro.2oTio.soOJ ceramics by solidstate methods, has been applied as a novel way to form zBCT-(1-z)BZT (O:Sz:~:J) ceramics by sintering the pre-calcined Bao.7oCao.3oTi0J and BaZro.2oTio.soOJ powders. A new phase diagram of the zBCT-(1-z)BZT (0$z:S1) has been constructed by combing structural and functional property measurements. It indicates a vertical orthorhombic phase region separating rhombohedral and tetragonal phases below the Curie temperature. The highest piezoelectric properties have been observed for z=0.5 ceramics at room temperature, due to the increased potential polarization directions in the vicinity of the orthorhombic to tetragonal phase boundary.
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Koju, Naresh. "Smart Piezoelectric Calcium Phosphates for Orthopedic, Spinal-fusion and Dental Applications." University of Toledo / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1524047236280822.
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Schröder, Mathias. "Conductive Domain Walls in Ferroelectric Bulk Single Crystals." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-142571.
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Ferroic materials play an increasingly important role in novel (nano-)electronic applications. Recently, research on domain walls (DWs) received a big boost by the discovery of DW conductivity in bismuth ferrite (BiFeO3 ) and lead zirconate titanate (Pb(Zrx Ti1−x )O3) ferroic thin films.
These achievements open a realistic and unique perspective to reproducibly engineer conductive paths and nanocontacts of sub-nanometer dimensions into wide-bandgap materials. The possibility to control and induce conductive DWs in insulating templates is a key step towards future innovative nanoelectronic devices [1]. This work focuses on the investigation of the charge transport along conductive DWs in ferroelectric single crystals. In the first part, the photo-induced electronic DC and AC charge transport along such DWs in lithium niobate (LNO) single crystals is examined. The DC conductivity of the bulk and DWs is investigated locally using piezoresponse force microscopy (PFM) and conductive AFM (c-AFM). It is shown that super-bandgap illumination (λ ≤ 310 nm) in combination with (partially) charged 180° DWs increases the DC conductivity of the DWs up to three orders of magnitude compared to the bulk. The DW conductivity is proportional to the charge of the DW given by its inclination angle α with respect to the polar axis. The latter can be increased by doping the crystal with magnesium (0 to 7 mol %) or reduced by sample annealing. The AC conductivity is investigated locally utilizing nanoimpedance microscopy (NIM) and macroscopic impedance measurements.
Again, super-bandgap illumination increases the AC conductivity of the DWs. Frequency-dependent measurements are performed to determine an equivalent circuit describing the domains and DWs in a model system. The mixed conduction model for hopping transport in LNO is used to analyze the frequency-dependent complex permittivity. Both, the AC and DC results are then used to establish a model describing the transport along the conductive DW through the insulating domain matrix material. In the last part, the knowledge obtained for LNO is applied to study DWs in lithium tantalate (LTO), barium titanate (BTO) and barium calcium titanate (BCT) single crystals. Under super-bandgap illumination, conductive DWs are found in LTO and BCT as well, whereas a domain-specific conductivity is observed in BTO.
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Schifferová, Zuzana. "Příprava kompozitních vláknitých struktur metodou elektrostatického zvlákňování pro piezoaplikace." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2019. http://www.nusl.cz/ntk/nusl-400447.
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Polymer and composite polymer-ceramic nanofibers were prepared by electrospinning process. Solution of 20 wt.% polyvinylidene fluoride (PVDF) in a mixture of dimethyl sulfoxide (DMSO) and acetone in the ratio of 7:3 was chosen as the most suitable precursor. When preparing composite nanofibers, 20 wt.% of barium calcium zirconate titanate (BCZT) or barium titanate (BT) nanoparticles was added to this PVDF solution. Given parameters were defined as the most suitable for the process of electrospinning: voltage of 50 kV, feeding rate of 30 l/min, distance between emitter and collector of 20 cm and needle diameter of 17 G. The effect of polymer molecular weight and the rotation speed of collector was also studied. Various properties of prepared samples were studied: morphology and fiber diameter, phase composition with the use of x-ray diffraction and Fourier transform infrared spectroscopy and also chosen electrical properties. Lower fiber diameters appeared with lower polymer molecular weight and higher rotation speed of the collector. These parameters resulted in higher percentage of the piezoelectric phase as well. The smallest achieved fiber diameter was around 300 nm, the highest percentage of phase was 92 % and the highest piezoelectric constant had a value of 16 pC/N. Composite fibers filled with BT particles showed better properties that the ones filled with BCZT particles.
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Santos, Jerre Cristiano Alves dos. "Estudo do comportamento PTCR em cerâmicas de BCT dopadas com íons terra raras." Universidade Federal de Sergipe, 2012. https://ri.ufs.br/handle/riufs/5346.
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Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorBarium titanate (BaTiO3 - BT) is a ferroelectric material with important technological applications. When partially doped with trivalent cations at the barium sublattice or pentavalent at the titanium sublattice, BaTiO3-based ceramics exhibit a semiconductive character, accompanied by a Positive Temperature Coefficient of Resistivity (PTCR). Several ways of BT modifications have been proposed in literature, as example, the use of different synthesis methods and the doping with different ions. Therefore, in the present work we have as objective the synthesis, sintering and electrical characterization of the rare earth ions (RE = La3+, Y3+, Er3+, Nd3+ e Eu3+) doped barium calcium titanate ceramics (Ba0,77Ca0,227RE0,003TiO3 BCT_RE) in order to study mainly the PTCR behavior. The powder synthesis was done by the polymeric precursor method followed by the sinterization at reducing atmosphere during the heating up ramp and different atmosphere during cooling down ramp in order to investigate the atmosphere and dopant effect on PTCR behavior. The characterization was done using the Differential Thermal Analysis, Thermogravimetry, Scanning Differential Calorimetry, X-ray Powder Diffraction, Scanning Electron Microscopy and Impedance Spectroscopy techniques. The calcined powder at 600ºC/4h presented majority BCT phase and after sintering at 1350ºC/6h, a small amount of Ba6Ti17O40 phase was observed. The sintered ceramics presented a homogeneous grain size distribution but with the presence of a secondary phase at the grain boundary for all compositions, and Curie temperature at about 120ºC. The PTCR characteristics of the ceramics were studied as a function of the sintering atmosphere and dopant type. In summary, all the samples, exception of the Eu doped samples, presented PTCR behavior in all the studied conditions. .
O titanato de bário (BaTiO3 - BT) é um material ferroelétrico com importantes aplicações tecnológicas. Quando dopado com íons trivalentes no sítio do bário ou pentavalentes no sítio do titânio, cerâmicas de BaTiO3 exibem um caráter semicondutor, acompanhado por um coeficiente positivo da resistência com o aumento da temperatura (PTCR). Diversas formas de modificação do BT têm sido sugeridas na literatura, por exemplo, a utilização de diferentes métodos de síntese e a dopagem com diferentes íons. Dessa forma, no presente trabalho tivemos como objetivo a síntese, a sinterização e a caracterização elétrica de cerâmicas de titanato de bário e cálcio (Ba0,77Ca0,227RE0,003TiO3 BCT_RE) dopados com íons terras raras (RE = La3+, Y3+, Er3+, Nd3+ e Eu3+), visando principalmente o estudo do comportamento PTCR. A síntese dos pós foi realizada pelo método dos precursores poliméricos, seguido pela sinterização em atmosfera redutora durante o aquecimento e diferentes atmosferas no resfriamento com o intuito de investigar a influência da atmosfera e do dopante no comportamento PTCR. A caracterização foi feita utilizando as técnicas de Análise Térmica Diferencial, Termogravimetria, Calorimetria Exploratória Diferencial, Difração de Raios X, Microscopia Eletrônica de Varredura e Espectroscopia de Impedância. Os pós calcinados a 600ºC/4h apresentaram fase majoritária BCT e após sinterizados a 1350ºC/6h foi observada a presença da fase Ba6Ti17O40. As cerâmicas sinterizadas apresentaram uma distribuição homogênea de tamanho de grão, porém com a presença de uma segunda fase na região de contorno de grão para todas as composições, com temperatura de Curie em torno de 120ºC. As características PTCR das cerâmicas foram estudadas em função da atmosfera de sinterização e do tipo do dopante. Em resumo, todas as amostras, com exceção das dopadas com Eu, apresentaram comportamento PTCR para todas as condições estudadas.
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Silva, Ronaldo Santos da. "Síntese e propriedades dielétricas de cerâmicas nanoestruturadas de Ba1xCaxTiO3 (0 menor igual x menor igual 0.30) sinterizadas a laser." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-19092007-100742/.
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Pós nanocristalinos de Ba1-xCaxTiO3(0≤ x ≤ 0.30) foram sintetizados pela primeira vez por meio do método dos precursores poliméricos modificados, em temperaturas relativamente baixas (500°C). Para a densificação dos corpos cerâmicos duas técnicas distintas foram utilizadas: a sinterização convencional, utilizando um forno elétrico; e a sinterização a laser, na qual um laser de CO2 foi utilizado como principal fonte de calor. Os corpos cerâmicos sinterizados pelas duas técnicas apresentaram um tamanho médio de grãos em torno de 500 nm, porém uma maior densidade relativa foi obtida nas cerâmicas sinterizadas a laser, chegando a 99%, além de boa transparência, ∼42% a 940 nm para a amostra com 30 mol% de Ca com espessura de 0.5 mm. Também verificamos por meio de simulação numérica, que a equação de condução de calor na aproximação linear, considerando uma fonte de calor com perfil gaussiano, descreve qualitativamente o comportamento observado durante a sinterização a laser no seu estágio final. Por meio da técnica de espectroscopia de impedância foi feita a caracterização dielétrica dos corpos cerâmicos, nos quais três pontos principais foram estudados: i) o efeito do tamanho de grãos; ii) a influência da concentração de Ca; e iii) a influência do método de sinterização. Com a variação do tamanho do grão foram observadas mudanças na intensidade do pico de transição ferro-paraelétrica, na temperatura de Curie e na permissividade relativa à temperatura ambiente. Para concentrações de Ca até 15 mol%, as cerâmicas apresentaram uma transição de Curie estreita semelhante ao BaTiO3,enquanto que para concentrações maiores, uma transição de fase difusa foi observada. A sinterização a laser resultou em corpos cerâmicos com constante dielétrica 30% maior, e menor perda dielétrica do que as cerâmicas sinterizadas convencionalmente. Finalmente, foi proposto um modelo baseando-se na formação de vacâncias de oxigênio para o aumento da condutividade elétrica com a substituição de Ca.Ba1-xCaxTiO3 (0 ≤ x ≤ 0.30) nanocrystalline powders were successfully synthesized for the first time at relative low temperature (500 °C) by a modified polymeric precursor method. The densification of the ceramics was made by two distinct techniques: conventional sintering using an electric furnace; and by a laser sintering process in which a CO2 laser is used as the main heating source. It was achieved dense ceramics with an average grain size about 500 nm from both techniques. However, the laser sintered ceramics presented a higher relative density (99 %) and a transparency of 42% at 940 nm in the sample with 30 mol% of Ca. By numerical simulation of the thermal conduction equation on the linear approximation case and taking account a thermal source with a gaussian profile, it was possible to describe qualitatively the final stage of the laser sintering process. The dielectric characterization of the ceramic bodies were carried out by the impedance spectroscopy technique and three main effects were studied: i) the grain size effect; ii) the Ca concentration influence; and, iii) the sintering technique influence. Modifying the grain size led to changes in the ferro-paraelectric transition magnitude, on the Curie temperature value and in the relative permittivity at room temperature. For Ca2+ concentrations up to 15 mol% the sintered ceramics presented a sharp Curie transition like BaTiO3,while for higher Ca concentrations a diffuse phase transition was observed. The laser sintered ceramics presented a dielectric constant 30% higher than the conventional sintering and a lower dielectric loss. Finally, we have proposed a model based on the oxygen vacancies formation to explain the conductivity increase with the Ca2+ substitution.
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Mhaifid, Touria. "Etude expérimentale des propriétés électrooptiques de la solution solide Ba0,97Sr0,03TiO3 et contribution au calcul des coefficients élastooptiques : application au calcul des coefficients électrooptiques de BaTiO3 et Ba0,97Sr 0,03TiO3." Dijon, 1996. http://www.theses.fr/1996DIJOS043.
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Jusqu'à présent BaTiO3 a été utilisé, pour ses propriétés photoréfractives, dans sa phase quadratique 9°C, 134°C. La limite inférieure de cette gamme de température représente un inconvénient majeur pour des applications industrielles où tous les composants fonctionnent jusqu'à -20°C. D'après les études antérieures faites au laboratoire la substitution des ions Ba par des ions Sr abaisse les températures de transitions du matériau sans changer ses propriétés photoexcitatrices. Une solution solide de Ba1-xSr TiO3 (BST) apparait comme une solution possible si la substitution ne s'accompagne pas d'une réduction des propriétés électrooptiques. La partie expérimentale de ce travail est consacrée à l'étude de l'effet électrooptique de Ba0,97Sr0,03 TiO3 (BST). Les coefficients r113 et r333 ont été déterminés en tenant compte de l'effet piézoélectrique du matériau r232 n'étant pas affecté par cette correction. Les principaux résultats sont les suivants: comme pour BaTiO3, les coefficients diminuent quand la longueur d'onde augmente. Cette dépendance a été expliquée qualitativement par un modèle de Sellmeier. R113, r333 et Ɛc augmentent avec la température, tandis que r232 et Ɛa diminuent. Ces résultats sont en accord avec le modèle de Didomenico. En conclusion BST (à 3% de Sr) a des propriétés électrooptiques comparables à celles de BaTiO3 et une température de transition orthorhombique-quadratique plus basse. L'obtention de BST plus riche en SR (20%) devrait permettre de disposer d'un matériau utilisable jusqu'à -20°C. La partie théorique présente un calcul original de tous les coefficients élastooptiques et électrooptiques de BaTiO3 et BST. Le modèle utilisé est un modèle microscopique d'ion polarisable qui tient compte de l'anisotropie des polarisabilités électroniques des ions compares à l'expérience, les résultats obtenus ont un bon ordre de grandeur. Ce calcul peut être amélioré en utilisant un modèle plus complet comportant plus de paramètres ajustables
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Bernhardt, Sylvie. "Gyromètre a fibre a double conjugaison de phase - étude d'un nouveau matériau photorefractif - réalisation d'un démonstrateur." Phd thesis, Université Paris Sud - Paris XI, 2001. http://pastel.archives-ouvertes.fr/pastel-00715875.
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Le remplacement de la fibre monomode a maintien de polarisation par de la fibre monomode standard dans les gyroscopes a fibre est un véritable enjeu économique. En effet, il permettrait a ces systèmes d'être compétitifs au niveau du coût sur le marche des centrales de navigations inertielles actuellement domine par les gyroscopes laser. Cependant, les problèmes de non réciprocités et d'effondrement du signal provoqués par l'utilisation de ce type de fibre n'ont pas été résolus de façon satisfaisante à ce jour. C'est a ce niveau que l'utilisation de la double conjugaison de phase apparaît comme une solution intéressante. L'objectif de ce travail consistait à valider cette solution d'une part en mettant au point un cristal photoréfractif adapte à cette application et d'autre part en insérant un miroir a double conjugaison de phase dans un gyroscope commercial fonctionnant a 850 mn. Dans un premier temps, nous avons donc etudie un nouveau cristal photorefractif : le titanate de barium calcium (bct) dont l'interet repose sur le fait qu'il ne subit pas de transition de phase de 120\ a 98\ c, contrairement au cristal de titanate de baryum dont il est dérivé. Ce cristal, généralement utilise pour la conjugaison de phase en raison de sa bonne efficacité est en effet détruit si sa température devient inférieure a 10\ c. Notre étude a permis de démontrer les bonnes propriétés photorefractives de ce matériau (coefficients electro-optiques élevés, sensibilité proche infrarouge) et de comprendre les différences de comportement par rapport au titanate de baryum. Dans un second temps, nous avons étudié et optimise un miroir a double conjugaison de phase réalisé avec un cristal de titanate de baryum que nous avons ensuite insere dans un gyromètre a fibre. Ainsi, nous avons pu montrer que le gyrometre a double conjugaison de phase permet de mesurer des rotations et n'introduit pas de non-reciprocités supérieures a la précision du montage que nous avons utilise (200 \/h).
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Szu-MinChen and 陳思敏. "Impedance Spectroscopy Analysis of Mn-Doped Barium Calcium Titanate Ceramics." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/ze4zpz.
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碩士國立成功大學
資源工程學系
106
In this study, calcium-doped barium titanate (BCT) powders were used as the raw materials to study different amounts of acceptor doping effects on the microstructure, crystal structure, and electrical properties of BCT. The A/B ratio of (Ba0.92Ca0.08)Ti1.005O3 was set for Ti-excess to prevent Ca doping onto the B-site. Powder of (Ba0.92Ca0.08)Ti1.005O3 was calcined at 1100°C which temperature can make the powder no second phase. Based on the Rietveld analysis results, Ca in the BCT mainly entered A-site to replace Ba. To simulating the MLCC sintering condition, the BCT ceramics should be sintered in reduction atmosphere to prevent the Ni electrode oxidation, and we also add different amounts of MnCO3 as acceptor to prevent the ceramic samples from semiconduction. The grain sizes after sintering are approximately 0.36 μm which fits the MLCC condition. In this study, We use two RQ equivalent circuit model to fit the impedance spectroscopy data, and the results meet the Curie-Weiss behavior. According to the impedance spectroscopy data, the grain and grain boundary conductivity of acceptor-doped BCT ceramics is determined by Vo ̈ and e' respectively. With the increase of the amount of addition, the grain and the grain boundary conductivity tends to increase. The similar grain and grain boundary conductivity of BCT ceramics are due to maintain the electric neutrality. While the depletion layer and grain boundary barrier height are tend to decrease as the amounts of acceptor increase. The comprehensive conclusions show that the amounts of acceptor (MnCO3) has a certain influence on the electrical analysis calculated by the impedance spectroscopy analysis.
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Tsung-HaoChen and 陳琮皓. "Study on the crystal structure, microstructure, and electrical properties of calcium doped barium titanate." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/6jg624.
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碩士國立成功大學
資源工程學系
106
In this study, commercial calcium-doped barium titanate (BCT) powders were used as the raw materials to study different amounts of calcium doping effects on the microstructure, crystal structure, and electrical properties. The experimental results showed that all samples can be densified in a reducing atmosphere and the average grain sizes were about 280-300 nm with no significant difference. No secondary phase was observed in the samples. Based on the Rietveld analysis results, Ca in the BCT mainly entered A-site to replace Ba, and the doped Dy entered B-site as the acceptor. For the BCT doped with Dy3+, the grains exhibited core-shell structure, and the laminar domains were observed in the core region. It may be due to the doped Dy3+ initially located near the grain boundaries and then diffused into the grains during sintering to form the core-shell structure. The Curie temperature and dielectric constant increased with increasing CaO content. The Curie temperature was shifted to a higher temperature by doping Dy3+ due to the internal stress generated by the core-shell structure. No significant difference in the conductivity was observed for the BCT with different CaO content. In comparison of other compositions reported in the literatures, the substitution of Ca2+ for Ba2+ can significantly increase the conductivity activation energy of grain because the conductivity at high temperature was dominated by V_Ba^' rather than V_O^(••). It suggests that Ca2+ doping can effectively inhibit the formation of oxygen vacancy. No significant depletion layer thickness and the height of the grain boundary energy barrier were found because the carrier concentrations were the same for BCT doped with same Dy content.
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Kumar, Sanjiv. "Chemical Characterisation Of The Surfaces And Interfaces Of Barium Titanate And Related Electronic Ceramics." Thesis, 2006. https://etd.iisc.ac.in/handle/2005/321.
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This thesis deals with the investigations on the atomic composition, chemical surface states and microstructural features of barium titanate and other electronic ceramics namely barium polytitantes, calcium manganites and magnesium calcium titanate by surface analytical techniques. After presenting a brief introduction on the ceramic materials studied in terms of their crystal structures, electrical properties, nonstoichiometry and interfacial characteristics, the thesis describes the synthesis of the ceramics and the methodology of the different surface analytical techniques utilized such as backscattering spectrometry (BS), an ion beam analysis (IBA) technique, X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDS). The XPS investigations on the chemical surface states of polycrystalline barium titanate having well-defined electrical characteristics reveal the prevalence of Ba in two distinct chemical environments : the one corresponding to the lower binding energy is related to the dielectric while the other having higher binding energy is correlated to semiconducting properties of the ceramics. Processes such as abrasion or polishing make the surfaces more reactive and susceptible to atmospheric contamination. Sputter cleaning causes surface modification leading to changes in the Ba (3d) and Ti (2p) spectra. Studies on the surface atomic composition by BS and microstructural features of doped barium titanate ceramics reveal their interfacial characteristics in terms segregation of dopants or metal ion constituents. Surfaces of these ceramics exhibit cationic as well as anionic nonstoichiometry depending on the processing steps involved. Ceramics synthesized by oxalate precursor route are Ti-rich while those prepared by gel-to-crystallite method are Ba-rich. These are correlated to the chemical processes and background impurities which in turn control the microstructures. Barium titanate substitued with > 1 at. % Mn are deficient in oxygen and exist as the hexagonal polymorph. Acceptors segregate at the grain boundaries accompanied by the enrichment of Ti leading to PTCR or GBLC characteristics. The oxygen nonstoichiometry prevailing in the surface regions of differently processed calcium manganites is investigated by way of depth profile measurements involving 16O(a,a) 16O resonant scattering. These studies reveal extensive compositional heterogeneity across the surface layers particularly in the manganite specimens annealed in lower po2 leading to the stabilization of brownmillerite phase. Two of the microwave dielectric ceramics namely dibarium nona-titanate and barium tetra-titanate with suitable variations in Ba:Ti ratios have been synthesized by the carbonate-gel precipitation. The corresponding dense ceramics have high permittivity (~ 52) and low temperature coefficient of permittivity (TCK ~ 5 ppm /0C). Extensive miscibility between the ilmenite-type MgTiO3 and perovskite-type CaTiO3 over a wide compositional range is brought about by the simultaneous equivalent substitution of Al3+ + La3+. The resulting (Mg1-(x+y)CaxLay)(Ti1-yAly)O3 ceramics exhibit improved microwave dielectric properties by way of high permittivity, low TCK and high quality factor. The microarea elemental distribution and chemical surface state studies reveal the complexity in the Mg/Ca distribution and its correlation with the solid state miscibility as well as dielectric properties. The discontinuous changes in the local site symmetry of the cationic substituents in these ceramics have been investigated by the photoluminescence spectra using Pr3+ as the emission probe.
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Kumar, Sanjiv. "Chemical Characterisation Of The Surfaces And Interfaces Of Barium Titanate And Related Electronic Ceramics." Thesis, 2006. http://hdl.handle.net/2005/321.
Full textAbstract:
This thesis deals with the investigations on the atomic composition, chemical surface states and microstructural features of barium titanate and other electronic ceramics namely barium polytitantes, calcium manganites and magnesium calcium titanate by surface analytical techniques. After presenting a brief introduction on the ceramic materials studied in terms of their crystal structures, electrical properties, nonstoichiometry and interfacial characteristics, the thesis describes the synthesis of the ceramics and the methodology of the different surface analytical techniques utilized such as backscattering spectrometry (BS), an ion beam analysis (IBA) technique, X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDS). The XPS investigations on the chemical surface states of polycrystalline barium titanate having well-defined electrical characteristics reveal the prevalence of Ba in two distinct chemical environments : the one corresponding to the lower binding energy is related to the dielectric while the other having higher binding energy is correlated to semiconducting properties of the ceramics. Processes such as abrasion or polishing make the surfaces more reactive and susceptible to atmospheric contamination. Sputter cleaning causes surface modification leading to changes in the Ba (3d) and Ti (2p) spectra. Studies on the surface atomic composition by BS and microstructural features of doped barium titanate ceramics reveal their interfacial characteristics in terms segregation of dopants or metal ion constituents. Surfaces of these ceramics exhibit cationic as well as anionic nonstoichiometry depending on the processing steps involved. Ceramics synthesized by oxalate precursor route are Ti-rich while those prepared by gel-to-crystallite method are Ba-rich. These are correlated to the chemical processes and background impurities which in turn control the microstructures. Barium titanate substitued with > 1 at. % Mn are deficient in oxygen and exist as the hexagonal polymorph. Acceptors segregate at the grain boundaries accompanied by the enrichment of Ti leading to PTCR or GBLC characteristics. The oxygen nonstoichiometry prevailing in the surface regions of differently processed calcium manganites is investigated by way of depth profile measurements involving 16O(a,a) 16O resonant scattering. These studies reveal extensive compositional heterogeneity across the surface layers particularly in the manganite specimens annealed in lower po2 leading to the stabilization of brownmillerite phase. Two of the microwave dielectric ceramics namely dibarium nona-titanate and barium tetra-titanate with suitable variations in Ba:Ti ratios have been synthesized by the carbonate-gel precipitation. The corresponding dense ceramics have high permittivity (~ 52) and low temperature coefficient of permittivity (TCK ~ 5 ppm /0C). Extensive miscibility between the ilmenite-type MgTiO3 and perovskite-type CaTiO3 over a wide compositional range is brought about by the simultaneous equivalent substitution of Al3+ + La3+. The resulting (Mg1-(x+y)CaxLay)(Ti1-yAly)O3 ceramics exhibit improved microwave dielectric properties by way of high permittivity, low TCK and high quality factor. The microarea elemental distribution and chemical surface state studies reveal the complexity in the Mg/Ca distribution and its correlation with the solid state miscibility as well as dielectric properties. The discontinuous changes in the local site symmetry of the cationic substituents in these ceramics have been investigated by the photoluminescence spectra using Pr3+ as the emission probe.
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Nguyen, Tyler. "Magneto-Electric Nanoparticles Cobalt Ferrite (CoFe2O4) -- Barium Titanate (BaTiO3) for Non-Invasive Neural Modulations." Diss., 2020. http://hdl.handle.net/1805/24094.
Full textAbstract:
Indiana University-Purdue University Indianapolis (IUPUI)Non-invasive brain stimulation is valuable for studying neural circuits and treating various neurological disorders in human. However, current technologies of noninvasive brain stimulation usually have low spatial and temporal precision and poor brain penetration, which greatly limit their application. A new class of nanoparticles known as magneto-electric nanoparticles (MENs) is highly efficient in coupling an externally applied magnetics wave with generating local electric fields for neuronal activity modulation. Here, a new type of MENs was developed that consisted of CoFe2O4- BaTiO3 and had excellent magneto-electrical coupling properties. Calcium imaging technique was used to demonstrate their efficacy in evoking neuronal activity in organotyic and acute cortical slices that expressed GCaMP6 protein. For in vivo noninvasive delivery of MENs to brain, fluorescently labeled MENs were intravenously injected and attracted to pass through blood brain barrier to a targeted brain region by applying a focal magnet field. Magnetic wave (~450 G at 10 Hz) applied to mouse brain was able to activate cortical network activity, as revealed by in vivo two-photon and mesoscopic imaging of calcium signals at both cellular and global network levels. The effect was further confirmed by the increased number of c-Fos expressing cells after magnetic stimulation. Histological analysis indicated that neither brain delivery of MENs nor the subsequent magnetic stimulation caused any significant increases in the numbers of GFAP and IBA1 positive astrocytes and microglia in the brain. MENs stimulation also show high efficacy in short-term pain relieve when tested with a tibial nerve injury mouse model. The study demonstrates the feasibility of using MENs as a novel efficient and non-invasive technique of brain stimulation, which may have great potential for translation.
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Jayanthi, S. "Dielectric Titanate Ceramics : Contributions From Uncommon Substituents And Microstructural Modifications." Thesis, 2006. https://etd.iisc.ac.in/handle/2005/392.
Full textAbstract:
This thesis deals with the investigations on the dielectric properties of polycrystalline ceramics having uncommon substitutions in barium titanate and other related phases of BaTiO3-CaTiO3, MgTiO3-CaTiO3 and MgTiO3-BaTiO3 systems. After presenting a brief introduction on the ceramic materials studied in terms of their crystal structures, electrical properties, nonstoichiometry and microstructural characteristics. The thesis describes the synthesis of the ceramics and the methodology of different techniques utilized in characterizing the samples. Barium calcium titanate was synthesized through novel wet chemical techniques and the dielectric properties of calcium substituted barium titanate do not reveal multi-site occupancy whereas they are predominantly influenced by the A/B cationic ratio. The role of transition metals of the 3d series from vanadium (Z=23) to zinc (Z=30) in modifying the crystallographic phase content, microstructure and the dielectric properties of BaTiO3 ceramics containing 10 at% impurities were studied. All the transition metals brought about the phase conversion to hexagonal BaTiO3, although no systematics could be arrived at relating the hexagonal content to the 3d electronic configuration of the impurities. The relaxor dielectrics arising from the titanate solid solution with uncommon substitution and its interconversion to normal ferroelectrics is studied. The effects of cationic substitutions of iron and niobium for titanium in BaTiO3 pervoskite lattice in crystal symmetry and dielectric properties were investigated. The above dielectric characteristics are comparable in a converse way to those of the well known Pb(Mg1/3Nb2/3)O3-PbTiO3 system wherein the relaxor behaviour occurs within the lower lead titanate compositional limits. The modification in -T characteristics of positive temperature coefficient in resistance (PTCR) by the addition of segregative additives such as B2O3, Al2O3 etc in BaTiO3 and its conversion to grain boundary layer capacitance is studied. The presence of Al-related hole centers at the grain boundary regions resulted in charge redistribution across the modified phase transition temperatures due to symmetry-related vibronic interactions, which result in broad PTCR characteristics extending to higher temperatures. The processing of high permittivity ceramics by the manipulation of microstructural features in semiconducting BaTiO3 is studied wherein the grain boundary layer effect superimposed with the contributions from the barrier layers formed during electroding related to microstructure is proposed to be responsible for the unusual high permittivity in semiconducting BaTiO3. The influence of Mg2+ as a substituent in modifying the crystallographic phase contents, microstructure and the dielectric properties of (Ba1-xMgx)TiO3 ceramics, (x ranging from zero to 1.0 ) is studied. The results point to the dual occupancy of Mg2+ both in A and B sublattice and the role of oxygen vacancy as well as (Ti3+ –VO) defects in stabilization of hexagonal phase to lower temperatures. The microwave dielectrics of the BaMg6Ti6O19 phase formed in the compositional range of x=0.4 to 0.7 was investigated for suitable application in microwave dielectrics. Extensive miscibility between the ilmenite-type MgTiO3 and perovskite-type CaTiO3 over a wide compositional range is brought about by the simultaneous equivalent substitution of Al3+ and La3+. The resulting Mg1-(x+y)CaxLay)(Ti1-yAly)O3 ceramics exhibit improved microwave dielectric properties by way of high permittivity, low TCK and high quality factor. The elemental distribution reveals the complexity in the Mg/Ca distribution and its correlation with the solid state miscibility as well as dielectric properties. Microwave dielectric property of Mg4Al2Ti9O25 which is detected as secondary phase is studied in detail.
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Jayanthi, S. "Dielectric Titanate Ceramics : Contributions From Uncommon Substituents And Microstructural Modifications." Thesis, 2006. http://hdl.handle.net/2005/392.
Full textAbstract:
This thesis deals with the investigations on the dielectric properties of polycrystalline ceramics having uncommon substitutions in barium titanate and other related phases of BaTiO3-CaTiO3, MgTiO3-CaTiO3 and MgTiO3-BaTiO3 systems. After presenting a brief introduction on the ceramic materials studied in terms of their crystal structures, electrical properties, nonstoichiometry and microstructural characteristics. The thesis describes the synthesis of the ceramics and the methodology of different techniques utilized in characterizing the samples. Barium calcium titanate was synthesized through novel wet chemical techniques and the dielectric properties of calcium substituted barium titanate do not reveal multi-site occupancy whereas they are predominantly influenced by the A/B cationic ratio. The role of transition metals of the 3d series from vanadium (Z=23) to zinc (Z=30) in modifying the crystallographic phase content, microstructure and the dielectric properties of BaTiO3 ceramics containing 10 at% impurities were studied. All the transition metals brought about the phase conversion to hexagonal BaTiO3, although no systematics could be arrived at relating the hexagonal content to the 3d electronic configuration of the impurities. The relaxor dielectrics arising from the titanate solid solution with uncommon substitution and its interconversion to normal ferroelectrics is studied. The effects of cationic substitutions of iron and niobium for titanium in BaTiO3 pervoskite lattice in crystal symmetry and dielectric properties were investigated. The above dielectric characteristics are comparable in a converse way to those of the well known Pb(Mg1/3Nb2/3)O3-PbTiO3 system wherein the relaxor behaviour occurs within the lower lead titanate compositional limits. The modification in -T characteristics of positive temperature coefficient in resistance (PTCR) by the addition of segregative additives such as B2O3, Al2O3 etc in BaTiO3 and its conversion to grain boundary layer capacitance is studied. The presence of Al-related hole centers at the grain boundary regions resulted in charge redistribution across the modified phase transition temperatures due to symmetry-related vibronic interactions, which result in broad PTCR characteristics extending to higher temperatures. The processing of high permittivity ceramics by the manipulation of microstructural features in semiconducting BaTiO3 is studied wherein the grain boundary layer effect superimposed with the contributions from the barrier layers formed during electroding related to microstructure is proposed to be responsible for the unusual high permittivity in semiconducting BaTiO3. The influence of Mg2+ as a substituent in modifying the crystallographic phase contents, microstructure and the dielectric properties of (Ba1-xMgx)TiO3 ceramics, (x ranging from zero to 1.0 ) is studied. The results point to the dual occupancy of Mg2+ both in A and B sublattice and the role of oxygen vacancy as well as (Ti3+ –VO) defects in stabilization of hexagonal phase to lower temperatures. The microwave dielectrics of the BaMg6Ti6O19 phase formed in the compositional range of x=0.4 to 0.7 was investigated for suitable application in microwave dielectrics. Extensive miscibility between the ilmenite-type MgTiO3 and perovskite-type CaTiO3 over a wide compositional range is brought about by the simultaneous equivalent substitution of Al3+ and La3+. The resulting Mg1-(x+y)CaxLay)(Ti1-yAly)O3 ceramics exhibit improved microwave dielectric properties by way of high permittivity, low TCK and high quality factor. The elemental distribution reveals the complexity in the Mg/Ca distribution and its correlation with the solid state miscibility as well as dielectric properties. Microwave dielectric property of Mg4Al2Ti9O25 which is detected as secondary phase is studied in detail.
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Schröder, Mathias. "Conductive Domain Walls in Ferroelectric Bulk Single Crystals." Doctoral thesis, 2013. https://tud.qucosa.de/id/qucosa%3A28008.
Full textAbstract:
Ferroic materials play an increasingly important role in novel (nano-)electronic applications. Recently, research on domain walls (DWs) received a big boost by the discovery of DW conductivity in bismuth ferrite (BiFeO3 ) and lead zirconate titanate (Pb(Zrx Ti1−x )O3) ferroic thin films.
These achievements open a realistic and unique perspective to reproducibly engineer conductive paths and nanocontacts of sub-nanometer dimensions into wide-bandgap materials. The possibility to control and induce conductive DWs in insulating templates is a key step towards future innovative nanoelectronic devices [1]. This work focuses on the investigation of the charge transport along conductive DWs in ferroelectric single crystals. In the first part, the photo-induced electronic DC and AC charge transport along such DWs in lithium niobate (LNO) single crystals is examined. The DC conductivity of the bulk and DWs is investigated locally using piezoresponse force microscopy (PFM) and conductive AFM (c-AFM). It is shown that super-bandgap illumination (λ ≤ 310 nm) in combination with (partially) charged 180° DWs increases the DC conductivity of the DWs up to three orders of magnitude compared to the bulk. The DW conductivity is proportional to the charge of the DW given by its inclination angle α with respect to the polar axis. The latter can be increased by doping the crystal with magnesium (0 to 7 mol %) or reduced by sample annealing. The AC conductivity is investigated locally utilizing nanoimpedance microscopy (NIM) and macroscopic impedance measurements.
Again, super-bandgap illumination increases the AC conductivity of the DWs. Frequency-dependent measurements are performed to determine an equivalent circuit describing the domains and DWs in a model system. The mixed conduction model for hopping transport in LNO is used to analyze the frequency-dependent complex permittivity. Both, the AC and DC results are then used to establish a model describing the transport along the conductive DW through the insulating domain matrix material. In the last part, the knowledge obtained for LNO is applied to study DWs in lithium tantalate (LTO), barium titanate (BTO) and barium calcium titanate (BCT) single crystals. Under super-bandgap illumination, conductive DWs are found in LTO and BCT as well, whereas a domain-specific conductivity is observed in BTO.
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Sarkar, Asis. "Ferroelectric Perovskite Superlattices By Pulsed Laser Ablation." Thesis, 2007. https://etd.iisc.ac.in/handle/2005/654.
Full textAbstract:
Fabrication of artificially structured superlattices, when controlled on a nanoscale level, can exhibit enhanced dielectric properties over a wide temperature range. Possible fabrication of new functional devices based on the parametric values of dielectric constants of these heterostructures was the major motivation behind the work.
Chapter 1 gives a brief overview of ferroelectrics; their defining features and their commercial importance to electronic industry. An introduction to ferroelectric superlattices, their technological application and fundamental physics that influence the behavior of superlattices are provided.
Chapter 2 deals with the various experimental studies carried out in this research work. It gives the details of the experimental set up and the basic operation principles of various structural and physical characterizations of the materials prepared. A brief explanation of material fabrication, structural, micro structural and physical property measurements is discussed.
Chapter 3 involves fabrication of two-component ferroelectric superlattices consisting of Barium Titanate (BTO), and Strontium Titanate (STO) with nanoscale control of superlattice periodicities by high-pressure multi target pulsed laser deposition on Pt (111)/Ti/SiO2/Si (100) substrate. Superlattices with varying periodicities were fabricated and their compositional variation across the thin film and the interface width were studied using Secondary Ion Mass Spectrometry (SIMS). Fabrications of superlattice structure were supported by observation of satellite peaks in XRD corresponding to the coherent heterostructures. The microstructural analysis was carried out using cross-sectional scanning electron microscopy (SEM), and contact mode-AFM was used to image surface morphology and root-mean-square (rms) roughness of the thin film heterostructure.
Chapter 4 deals with ferroelectric studies of BTO/STO superlattices. The size dependent polarization behaviors of the superlattices are shown. The experimental realization of the dimensional range in which, the long-range coupling interaction dominates the overall polarization behavior of the system was studied. The dependence of average spontaneous polarization on the individual layer thickness, temperature and the dimensional range of interaction are discussed. The enhanced non-linear behaviors of the films were measured in terms of tunability. The dielectric phase transition behavior of superlattice structures of different periodicities was studied.
Chapter 5 focuses on fabrication of three-component ferroelectric superlattices consisting of Barium Titanate (BTO), Calcium Titanate (CTO) and Strontium Titanate (STO). The fabrications of superlattice structures were confirmed by the presence of satellite reflections in XRD analysis and a periodic concentration of Sr, Ba and Ca throughout the film in Depth profile of SIMS analysis. The microstructural analysis was carried out using cross-sectional scanning electron microscopy (SEM), and contact mode-AFM was used to image surface morphology and root-mean-square (rms) roughness of the thin film heterostructure.
The dielectric characteristic and polarization properties of the system are discussed. Large variations of lattice distortion in the consisting layers were achieved by varying the stacking sequence and superlattice periodicity. The influence of interfacial strain on enhancement of ferroelectric polarization was studied. The size dependence and the role of interfaces in the observed enhancements of the dielectric behaviors were highlighted. The tunability of about 55% was achieved in these systems and was higher than any of the single polycrystalline thin film of the constituent materials reported till date. The enhanced dielectric properties were thus discussed in terms of the interfacial strain driven polar region due to high lattice mismatch and electrostatic coupling due to polarization mismatch between individual layers.
Chapter 6 deals with the dielectric response, impedance spectroscopy and the DC leakage characteristics of the superlattice structures. All the heterostructures fabricated, exhibited low frequency dispersion, similar to that of the Jonscher’s universal type of relaxation behavior. The anomalous dispersion was observed in the imaginary dielectric constant at high frequencies. A Debye type relaxation behavior was observed in the impedance analysis at low temperatures, whereas, a departure from ideal ‘Debye’ type was noticed as the temperature was increased. The leakage currents of all the heterostructures were found to be a few orders less than the homogeneous single layer thin films. A space charge limited conduction was observed in al the superlattice structures fabricated.
Chapter 7 summarizes the present study and discusses about the future work that could give more insight into the understanding of the ferroelectric perovskite heterostructures.
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Sarkar, Asis. "Ferroelectric Perovskite Superlattices By Pulsed Laser Ablation." Thesis, 2007. http://hdl.handle.net/2005/654.
Full textAbstract:
Fabrication of artificially structured superlattices, when controlled on a nanoscale level, can exhibit enhanced dielectric properties over a wide temperature range. Possible fabrication of new functional devices based on the parametric values of dielectric constants of these heterostructures was the major motivation behind the work.
Chapter 1 gives a brief overview of ferroelectrics; their defining features and their commercial importance to electronic industry. An introduction to ferroelectric superlattices, their technological application and fundamental physics that influence the behavior of superlattices are provided.
Chapter 2 deals with the various experimental studies carried out in this research work. It gives the details of the experimental set up and the basic operation principles of various structural and physical characterizations of the materials prepared. A brief explanation of material fabrication, structural, micro structural and physical property measurements is discussed.
Chapter 3 involves fabrication of two-component ferroelectric superlattices consisting of Barium Titanate (BTO), and Strontium Titanate (STO) with nanoscale control of superlattice periodicities by high-pressure multi target pulsed laser deposition on Pt (111)/Ti/SiO2/Si (100) substrate. Superlattices with varying periodicities were fabricated and their compositional variation across the thin film and the interface width were studied using Secondary Ion Mass Spectrometry (SIMS). Fabrications of superlattice structure were supported by observation of satellite peaks in XRD corresponding to the coherent heterostructures. The microstructural analysis was carried out using cross-sectional scanning electron microscopy (SEM), and contact mode-AFM was used to image surface morphology and root-mean-square (rms) roughness of the thin film heterostructure.
Chapter 4 deals with ferroelectric studies of BTO/STO superlattices. The size dependent polarization behaviors of the superlattices are shown. The experimental realization of the dimensional range in which, the long-range coupling interaction dominates the overall polarization behavior of the system was studied. The dependence of average spontaneous polarization on the individual layer thickness, temperature and the dimensional range of interaction are discussed. The enhanced non-linear behaviors of the films were measured in terms of tunability. The dielectric phase transition behavior of superlattice structures of different periodicities was studied.
Chapter 5 focuses on fabrication of three-component ferroelectric superlattices consisting of Barium Titanate (BTO), Calcium Titanate (CTO) and Strontium Titanate (STO). The fabrications of superlattice structures were confirmed by the presence of satellite reflections in XRD analysis and a periodic concentration of Sr, Ba and Ca throughout the film in Depth profile of SIMS analysis. The microstructural analysis was carried out using cross-sectional scanning electron microscopy (SEM), and contact mode-AFM was used to image surface morphology and root-mean-square (rms) roughness of the thin film heterostructure.
The dielectric characteristic and polarization properties of the system are discussed. Large variations of lattice distortion in the consisting layers were achieved by varying the stacking sequence and superlattice periodicity. The influence of interfacial strain on enhancement of ferroelectric polarization was studied. The size dependence and the role of interfaces in the observed enhancements of the dielectric behaviors were highlighted. The tunability of about 55% was achieved in these systems and was higher than any of the single polycrystalline thin film of the constituent materials reported till date. The enhanced dielectric properties were thus discussed in terms of the interfacial strain driven polar region due to high lattice mismatch and electrostatic coupling due to polarization mismatch between individual layers.
Chapter 6 deals with the dielectric response, impedance spectroscopy and the DC leakage characteristics of the superlattice structures. All the heterostructures fabricated, exhibited low frequency dispersion, similar to that of the Jonscher’s universal type of relaxation behavior. The anomalous dispersion was observed in the imaginary dielectric constant at high frequencies. A Debye type relaxation behavior was observed in the impedance analysis at low temperatures, whereas, a departure from ideal ‘Debye’ type was noticed as the temperature was increased. The leakage currents of all the heterostructures were found to be a few orders less than the homogeneous single layer thin films. A space charge limited conduction was observed in al the superlattice structures fabricated.
Chapter 7 summarizes the present study and discusses about the future work that could give more insight into the understanding of the ferroelectric perovskite heterostructures.
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Garg, Rohini. "Structural, Ferroelectric, Piezoelectric and Phase Transition Studies of Lead Free (Na0.5Bi0.5)TiO3 Based Ceramics." Thesis, 2013. http://etd.iisc.ac.in/handle/2005/3446.
Full textAbstract:
Ferroelectric materials, especially the polycrystalline ceramics, are very promising material for a variety of applications such as high permittivity dielectrics, ferroelectric memories, piezoelectric sensors, piezoelectric/electrostrictive transducers, electrooptic devices and PTC thermistors. Among the ferroelectric based piezoelectric ceramics the lead–zirconate-titanate Pb(Zr1-xTix)O3 (PZT) have dominated transducer and actuator market due to its excellent piezoelectric and dielectric properties, high electromechanical coupling, large piezoelectric anisotropy, ease of processing and low cost. However, the toxicity of lead based compounds has raised serious environmental concerns and therefore has compelled the researchers to look for new lead free alternatives with good piezoelectric and ferroelectric properties. (Na0.5Bi0.5)TiO3 (NBT) and its solid solution is one of the leading lead free piezoceramic ceramics due to their interesting ferroelectric, piezoelectric, electromechanical and dielectric property. The parent compound NBT is a ferroelectric with a moderately high Curie temperature (~250 oC), large ferroelectric polarization (~40µC/cm2) polarization, promising piezoelectric properties with 0.08% strain and longitudinal piezoelectric coefficient (d33) ~ 80 pC/N. X-ray and neutron diffraction studies in the past have shown that NBT exhibits rhombohedral (R3c) at room temperature. Neutron diffraction studies have suggested that NBT undergo a gradual rhombohedral to tetragonal (P4bm) transformation in a temperature region 200-320 ºC. Though the structure and phase transition behavior of NBT has been extensively investigated for over six decades now, this subject has again become debatable in recent few years, with some group reporting formation of orthorhombic phase above room temperature and another group suggesting monoclinic distortion at room temperature using high resolution x-ray diffraction technique. Interestingly the intermediate orthorhombic instability, reported by electron diffraction studies, has never been captured by neutron diffraction method though neutron diffraction is an equally powerful tool for studying (oxygen) octahedral tilts in perovskites. Needless to mention, the understanding of the subtle structural distortions have great significance with regard to the determination of the structure-piezoelectric property correlations in NBT based piezoceramics. The present thesis deals with such subtle structural issues in great detail. The systems investigated in the thesis are Ca and Ba modified NBT. While the Ca modified system was chosen to understand the subtle orthorhombic instability that has been reported above room temperature (only) by detailed electron diffraction work, Ba-modified NBT is the most investigated among the NBT-derived piezoelectric material systems and this thesis attempts to address some of the very complex nature of the structure-piezoelectric property correlation of this system.
The first chapter of the thesis provides a brief introduction to the field of ferroelectrics, perovskite structure and their phase transition. A brief exposure to the conventional lead based relaxor ferroelectric and piezoelectric material is provided. A detailed overview of the existing knowledge related to room temperature structure of NBT and its phase transition studies with temperature has been discussed in the later part of this chapter. The second chapter includes various the experimental techniques that have been employed to synthesis and characterize the specimens under investigation.
The third chapter deals with the phase transition behaviour of Ca modified NBT as a function of composition and temperature in the dilute concentration region. This work was carried out with the view to obtain a better understanding and compliment the intrinsic high temperature orthorhombic instability in NBT reported by electron diffraction technique. Interestingly, inspite of the fact that neutron diffraction method is a very sensitive tool for investigating subtle change in the nature of octahedral tilt in oxide perovskites, the intermediate orthorhombic distortion proposed by the electron diffraction studies has so far never been captured in any of the neutron diffraction studies. In this work we have verified the genuineness of the intrinsic instability with regard to the non-polar orthorhombic structure using neutron powder diffraction by adopting a special strategy which helped in capturing the characteristic signatures (the superlattice reflections) of the orthorhombic phase in the neutron powder diffraction patterns. It was found that small fraction of Ca-substitution (8-10 mol %) was good enough to amplify the magnitude of the orthorhombic (Pbnm) distortion, without altering the sequence of the structural evolution with temperature of the parent compound (NBT) itself, and stabilizing it at the global length scale at lower temperatures than pure NBT. This chapter presents the innovative approach that was used to extract reliable information about the very complex phase transition behaviour, involving coexistence of the various similar looking but crystallographically different phases in different temperature regimes by Rietveld analysis of temperature dependent neutron powder diffraction pattern in conjunction with temperature dependent dielectric and ferroelectric characterization of the specimens. The detailed study revealed the following sequence of structural evolution with temperature: Cc+Pbnm →Pbnm
+ P4/mbm → P4/mbm →Pm3 m.
The fourth chapter gives a detail account of the structure-property correlations and the phase transition behaviour of (1-x)(Na0.5Bi0.5)TiO3 – (x)BaTiO3 (0≤x≤0.10), the most important solid solution series with NBT as reported in the literature. The phase transformation behaviour of this system has been investigated as a function of composition (0
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Garg, Rohini. "Structural, Ferroelectric, Piezoelectric and Phase Transition Studies of Lead Free (Na0.5Bi0.5)TiO3 Based Ceramics." Thesis, 2013. http://etd.iisc.ernet.in/2005/3446.
Full textAbstract:
Ferroelectric materials, especially the polycrystalline ceramics, are very promising material for a variety of applications such as high permittivity dielectrics, ferroelectric memories, piezoelectric sensors, piezoelectric/electrostrictive transducers, electrooptic devices and PTC thermistors. Among the ferroelectric based piezoelectric ceramics the lead–zirconate-titanate Pb(Zr1-xTix)O3 (PZT) have dominated transducer and actuator market due to its excellent piezoelectric and dielectric properties, high electromechanical coupling, large piezoelectric anisotropy, ease of processing and low cost. However, the toxicity of lead based compounds has raised serious environmental concerns and therefore has compelled the researchers to look for new lead free alternatives with good piezoelectric and ferroelectric properties. (Na0.5Bi0.5)TiO3 (NBT) and its solid solution is one of the leading lead free piezoceramic ceramics due to their interesting ferroelectric, piezoelectric, electromechanical and dielectric property. The parent compound NBT is a ferroelectric with a moderately high Curie temperature (~250 oC), large ferroelectric polarization (~40µC/cm2) polarization, promising piezoelectric properties with 0.08% strain and longitudinal piezoelectric coefficient (d33) ~ 80 pC/N. X-ray and neutron diffraction studies in the past have shown that NBT exhibits rhombohedral (R3c) at room temperature. Neutron diffraction studies have suggested that NBT undergo a gradual rhombohedral to tetragonal (P4bm) transformation in a temperature region 200-320 ºC. Though the structure and phase transition behavior of NBT has been extensively investigated for over six decades now, this subject has again become debatable in recent few years, with some group reporting formation of orthorhombic phase above room temperature and another group suggesting monoclinic distortion at room temperature using high resolution x-ray diffraction technique. Interestingly the intermediate orthorhombic instability, reported by electron diffraction studies, has never been captured by neutron diffraction method though neutron diffraction is an equally powerful tool for studying (oxygen) octahedral tilts in perovskites. Needless to mention, the understanding of the subtle structural distortions have great significance with regard to the determination of the structure-piezoelectric property correlations in NBT based piezoceramics. The present thesis deals with such subtle structural issues in great detail. The systems investigated in the thesis are Ca and Ba modified NBT. While the Ca modified system was chosen to understand the subtle orthorhombic instability that has been reported above room temperature (only) by detailed electron diffraction work, Ba-modified NBT is the most investigated among the NBT-derived piezoelectric material systems and this thesis attempts to address some of the very complex nature of the structure-piezoelectric property correlation of this system.
The first chapter of the thesis provides a brief introduction to the field of ferroelectrics, perovskite structure and their phase transition. A brief exposure to the conventional lead based relaxor ferroelectric and piezoelectric material is provided. A detailed overview of the existing knowledge related to room temperature structure of NBT and its phase transition studies with temperature has been discussed in the later part of this chapter. The second chapter includes various the experimental techniques that have been employed to synthesis and characterize the specimens under investigation.
The third chapter deals with the phase transition behaviour of Ca modified NBT as a function of composition and temperature in the dilute concentration region. This work was carried out with the view to obtain a better understanding and compliment the intrinsic high temperature orthorhombic instability in NBT reported by electron diffraction technique. Interestingly, inspite of the fact that neutron diffraction method is a very sensitive tool for investigating subtle change in the nature of octahedral tilt in oxide perovskites, the intermediate orthorhombic distortion proposed by the electron diffraction studies has so far never been captured in any of the neutron diffraction studies. In this work we have verified the genuineness of the intrinsic instability with regard to the non-polar orthorhombic structure using neutron powder diffraction by adopting a special strategy which helped in capturing the characteristic signatures (the superlattice reflections) of the orthorhombic phase in the neutron powder diffraction patterns. It was found that small fraction of Ca-substitution (8-10 mol %) was good enough to amplify the magnitude of the orthorhombic (Pbnm) distortion, without altering the sequence of the structural evolution with temperature of the parent compound (NBT) itself, and stabilizing it at the global length scale at lower temperatures than pure NBT. This chapter presents the innovative approach that was used to extract reliable information about the very complex phase transition behaviour, involving coexistence of the various similar looking but crystallographically different phases in different temperature regimes by Rietveld analysis of temperature dependent neutron powder diffraction pattern in conjunction with temperature dependent dielectric and ferroelectric characterization of the specimens. The detailed study revealed the following sequence of structural evolution with temperature: Cc+Pbnm →Pbnm
+ P4/mbm → P4/mbm →Pm3 m.
The fourth chapter gives a detail account of the structure-property correlations and the phase transition behaviour of (1-x)(Na0.5Bi0.5)TiO3 – (x)BaTiO3 (0≤x≤0.10), the most important solid solution series with NBT as reported in the literature. The phase transformation behaviour of this system has been investigated as a function of composition (0
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Bharathi, P. "Investigations into the Synthesis, Structural and Multifunctional Aspects of Ba0.85Ca0.15Zr0.1Ti0.9O3 and K0.5Na0.5NbO3 Ceramics." Thesis, 2016. http://etd.iisc.ac.in/handle/2005/3747.
Full textAbstract:
Non-centrosymmetric materials that can be polarized under applied mechanical stress or electric field are piezoelectric in nature and the phenomenon is called piezoelectric effect. They are broadly classified as direct and converse piezoelectric effects. Piezo-ceramics have a wide range of applications such as piezoelectric actuators, sensors, and transducers. Among piezoceramics, ferroelectric based materials are imperative owing to the existence of spontaneous polarization in these systems. Several materials are investigated starting from naturally occurring crystals to synthetic ceramics but are limited in their application range. The piezoelectric and ferroelectrics properties of the solid-solutions based on lead zirconate and lead titanate called lead zirconate titanate (PZT), lead magnesium niobate-lead titanate (PMN-PT), lead zinc niobate-lead titanate (PZN-PT) (near morphotrophic phase boundary (MPB))
demonstrate their potential for myriad device applications besides inciting a great deal of academic interest. They have been widely used for commercial applications such as ultra sound transducers, ultrasonic motors, fuel injector actuators, nano positioners in scanning electron microscope etc. However, these materials contain more than 60% lead by weight and volatization of Pb at higher temperature, and disposal of lead results in environmental pollution and are fatal to human health. This gave an insight to search for lead-free solid solutions covering a wide spectrum of applications akin to that of PZT. The search for alternatives to lead based piezoelectric materials is now being focused on modified barium titanates and alkali niobates in which the incidence of MPB was reported similar to that of PZT. In this thesis the results pertaining to the various investigations carried out on modified barium titanates, Ba(Zr0.2Ti0.8)O3- x(Ba0.7Ca0.3)TiO3(BCZT), and alkali niobates, potassium sodium niobate (KNN), are presented.
Especially, lead-free piezoelectric material Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3(BCZT) with x= 0.5 has attracted great attention due to its excellent piezoelectric properties. Contrary to the other Pb-free systems, the BZT–BCT phase diagram shows a Morphotropic Phase Boundary (MPB) characterized by the existence of a tri-critical point (TCP), which is also the case for PZT and PMN–PT. One drawback of the BZT–xBCT (x=0.5) is its high sintering temperature (where it exhibits the largest d33 of 550 – 620pC/N). Several methods have been adopted and various additives are being added to bring down the sintering temperature, since high d33 requires an optimized sintering temperature of around 1540oC which also shows excellent ferroelectric properties. However, the methods that were reported in the literature to synthesize the above materials do not guarantee compositional homogeneity and also there is a limitation in obtaining ceramics of enhanced grain size as the ceramics comprising larger grains are demonstrated to exhibit high piezoelectric coefficients. Therefore to address these issues, the simple soft chemical route was adopted to synthesize chemically homogenous powder and the influence of microstructure (grain size) and ferroelectric domains on piezoelectric properties of the BCZT at nano and micron sized crystallites was studied. The results obtained are classified into chapter 3 and chapter 4 accordingly apart from introduction, materials, and methods. Another challenging area of research in lead free piezoceramics for nanoscale device application is to synthesize materials and to visualize the piezoelectric properties at nanoscale with controlled shapes and sizes. For that, Mg2+ ion was chosen as the dopant especially on Ba2+ sites to synthesize
Ba0.95Mg0.05Zr0.1Ti0.9O3 (BMZT) nanocrystals, as MgO is known to be an effective grain growth inhibitor in many functional and structural ceramics. Therefore in the present thesis Mg2+ ion was chosen to exercise a strict control over the grain size. The results obtained from this title compound are discussed in chapter 5.
Another class of material is K0.5Na0.5NbO3 (KNN), which has been considered a good candidate for lead-free piezoelectric materials. KNN exhibits an MPB around 50% K and 50% Na separating two orthorhombic phases from the complete solid solution of NaNbO3 (Anti-ferroelectric) and KNbO3 (ferroelectric). The major problem associated with KNN ceramic is its complex densification process; difficulty in processing and volatilization of sodium at higher sintering temperature leading to stoichiometric discrepancy. To overcome these difficulties, in the present investigations, an attempt has been made to fabricate KNN ceramics by employing the liquid phase sintering method. In this chapter, B2O3 and borate based glass (0.5 Li2O - 0.5K2O- 2B2O3) were chosen to improve the densification, grain size and their effects on the physical properties of the KNN ceramics are discussed in chapter 6. In chapter 7, KNN crystallites (with size varying from nano to micrometers) were dispersed in the Polyvinylidene fluoride (PVDF) matrix to obtain a polymer/nano or micro crystal composites and the effect of nano and micron sized KNN fillers on the structural, dielectric and piezoelectric properties were investigated. The results obtained pertaining to these aforementioned investigations are organized as follows.
In Chapter 1, a brief introduction to the field of ferroelectricity, piezoelectricity, and piezoelectric materials. The emphasis has been on the ferroelectric based piezoelectric materials belonging to the perovskite family of oxides. A brief exposure to the conventional lead based piezoceramics, lead zirconate titanate (PZT) is discussed. Furthermore, drawbacks associated with lead based ceramics are highlighted and alternatives to PZT based ceramics such as modified barium titanate and alkali niobate solid solutions are focused, leading to the motivation and objectives of our work.
Chapter 2 describes the various experimental techniques that are employed to synthesize and characterize the materials under investigation.
Chapter 3 deals with details concerning the characterization of Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) nanocrystals prepared via complex oxalate precursor route at a relatively low temperature (800°C/5h). The phase formation temperature of BCZT at nanoscale was confirmed by thermogravimetric (TG), differential thermal analysis (DTA) followed by X-ray powder diffraction (XRD) studies. Fourier Transform Infrared (FTIR) spectroscopy was carried out to confirm the complete decomposition of oxalate precursor into BCZT phase. The XRD and profile fitting revealed the coexistence of cubic and tetragonal phases and was also corroborated by Raman study. Transmission electron microscopy (TEM) studies carried out at 800°C and 1000°C/5h heat treated BCZT powder revealed the crystallite size to be in the range of 20 – 50 nm and 40 – 200 nm respectively. The optical band gap for BCZT nanocrystalline powder was obtained using Kubelka Munk function and was found to be around 3.12 ± 0.02 eV and 3.03± 0.02 eV respectively for 800°C (20 – 50 nm) and 1000°C/5h (40 – 200 nm) heat treated samples. The piezoelectric properties were studied for two different crystallite sizes (30 and 70 nm) using piezoresponse force microscope (PFM). The d33 coefficients obtained for 30 nm and 70 nm sized crystallites were 4 pm/V and 47 pm/V respectively. These were superior to those of BaTiO3 nanocrystal (≈ 50 nm) and promising from the technological/industrial applications perspective.
Chapter 4 deals with the studies concerning the effect of microstructure (Grain size) and ferroelectric domains on physical properties of Ba0.85Ca0.15Zr0.1Ti0.9O3 ceramics. Fine powders comprising nanocrystallites of Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) were synthesized via oxalate precursor method which facilitated to obtain homogenous and large grain sized ceramics at a lower sintering temperature. The compacted powders were sintered at various temperatures in the range of 1200°C - 1500°C for an optimized duration of 10h. Interestingly the one that was sintered at 1450°C/10h exhibited well resolved Morphotrophic Phase Boundary (MPB). The average grain size associated with this sample was 30 µm accompanied by higher domain density mostly with 90° twinning. These were believed to make a significant contribution towards obtaining large strain of about 0.2 % and piezoelectric coefficient as high as 563 pC/N. The maximum force that was generated by BCZT ceramic (having 30 µm grain size) was found to be 161 MPa which is much higher than that of known actuator materials such as PZT (40 MPa) and NKN-5-LT (7 MPa).
Chapter 5 reports the details involving the synthesis, structural, optical, and piezoelectric response of lead free Ba0.95Mg0.05Zr0.1Ti0.9O3 nanocrystalline powder. Nanocrystalline powders of Ba1-xMgxZr0.1Ti0.9O3 (x=0.025 - 0.1) were synthesized via citrate assisted sol-gel method. Interestingly, the one with x=0.05 in the system Ba1-xMgxZr0.1Ti0.9O3 exhibited fairly good piezoelectric response apart from the other physical properties. The phase and structural confirmation of synthesized powder was established by X-ray powder diffraction (XRD) and Raman Spectroscopic techniques. Two distinct Raman bands i.e., 303 cm-1 and 723 cm-1 characteristic of the tetragonal phase were observed. Thermogravimetric analysis (TGA) was performed to evaluate the phase decomposition of the as-synthesized Ba0.95Mg0.05Zr0.1Ti0.9O3 sample as a function of temperature. The average crystallite size associated with Ba0.95Mg0.05Zr0.1Ti0.9O3 was calculated using Scherrer formula based on the XRD data and was found to be 25 nm. However, Scanning and Transmission Electron Microscopy studies revealed the average crystallite size to be in the range of 30-40 nm. Kubelka-Munk function was employed to determine the optical band gap of these nanocrystallites. The piezoelectric response of 26 pm/V was observed for Ba0.95Mg0.05Zr0.1Ti0.9O3 nanocrystal by Piezoresponse Force Microscopy (PFM) technique. Photoluminescence (PL) study carried out on these nanocrystals exhibited a blue emission (470 nm) at room temperature.
Chapter 6 describes the effect of the addition of B2O3 on the density, microstructure, dielectric, piezoelectric and ferroelectric properties of K0.5Na0.5NbO3 ceramics. Boron oxide (B2O3) addition to pre-reacted K0.5Na0.5NbO3 (KNN) powders facilitated swift densification at relatively low sintering temperatures which was believed to be a key to minimize potassium and sodium loss. The base KNN powder was synthesized via solid-state reaction route. The different amounts (0.1 to 1 wt %) of B2O3 were added, and ceramics were sintered at different temperatures and durations to optimize the amount of B2O3 needed to obtain KNN pellets with the highest possible density and grain size. The 0.1 wt% B2O3 added KNN ceramics sintered at 1100°C for 7h exhibited higher density (98%) with grain size of ~5 µm. Scanning electron microscopy (SEM) studies confirmed an increase in average grain size with increasing B2O3 content at the appropriate temperature of sintering and duration.
The B2O3 added KNN ceramics exhibited improved dielectric and piezoelectric properties at room temperature. For instance, 0.1 wt% B2O3 added KNN ceramic exhibited d33 value of 116 pC/N which is much higher than that of pure KNN ceramics. Interestingly, all the B2O3 added (0.1 to 1wt %) KNN ceramics exhibited polarization – electric field (P vs E) hysteresis loops at room temperature. The remnant polarization (Pr) and coercive field (Ec) values are dependent on the B2O3 content and crystallite size. The details pertaining to the effect of the addition of borate based glass (0.5 Li2O - 0.5K2O- 2B2O3) on the physical properties of K0.5Na0.5NbO3 ceramics are also reported in this chapter. The addition of powdered 0.5 Li2O - 0.5K2O- 2B2O3 (LKBO) glass (0.5 to 2 wt%) to potassium sodium niobate, K0.5Na0.5NbO3 (KNN) powder facilitated higher densification which resulted in improved physical properties that include dielectric, piezoelectric and ferroelectric. The required polycrystalline powders of KNN were synthesized through solid-state reaction route, while LKBO glass was obtained via the conventional melt-quenching technique. Pulverized glass was added to KNN powders in different wt% and compacted at room temperature and these were sintered around 1100°C. Indeed the addition of optimum amount (1 wt %) of LKBO glass to KNN ceramics facilitated lowering of sintering temperature accompanied by larger grains (8 µm) with improved density. The dielectric constant (εr) measured at room temperature was 475 (at 10 kHz), whereas it was only 199 for the LKBO glass free KNN. The piezoelectric coefficient (d33) was found to be 130 pC/N for 1wt% LKBO added glass, which was much higher than that of pure KNN ceramics (85 pC/N). Indeed, the LKBO glass added samples did exhibit well saturated P versus E hysteresis loops at room temperature. Though there was no particular trend observed in the variation of Pr with the increase in glass content, the Pr values were higher than those obtained for KNN ceramics. The improved physical properties of KNN ceramics encountered in these studies were primarily attributed to enhancement in density and grain size.
Chapter 7 presents a comparative study on the structural, dielectric and piezoelectric properties of nano and micron sized K0.5Na0.5NbO3 fillers in PVDF composites. Polymer nanocrystal composites were fabricated by embedding polyvinylidene fluoride (PVDF) with different vol% of K0.5Na0.5NbO3 (KNN) nanocrystallites using hot-pressing technique. For comparison, PVDF-KNN microcrystal composites of the same compositions were also fabricated which facilitated the crystallite size (wide range) effect studies on the dielectric and piezoelectric properties. The structural, morphological, dielectric, and piezoelectric properties of these nano and micro crystal composites were investigated. The incorporation of KNN fillers in PVDF at both nano and micrometer scale above 10vol% resulted in the formation of polar β-form of PVDF. The room temperature dielectric constant as high as 3273 at 100Hz was obtained for PVDF comprising 40 vol% KNN nanocrystallites due to dipole –dipole interactions (as the presence of β-PVDF is prominent), whereas it was only 236 for PVDF containing the same amount (40 vol%) of micron sized crystallites of KNN at the same frequency. Various theoretical models were employed to predict the dielectric constants of the PVDF-KNN nano and microcrystal composites. PVDF comprising 70 vol% micronmeter sized crystallites of KNN exhibited d33 value of 35pC/N, while the nanocrystal composites of PVDF-KNN did not exhibit any piezoelectric response perhaps due to unrelieved internal stress within each grain besides having less number of domain walls.
The Thesis ends with summary and conclusions, though each chapter is provided with conclusions and a complete list of references.
24
Bharathi, P. "Investigations into the Synthesis, Structural and Multifunctional Aspects of Ba0.85Ca0.15Zr0.1Ti0.9O3 and K0.5Na0.5NbO3 Ceramics." Thesis, 2016. http://etd.iisc.ernet.in/2005/3747.
Full textAbstract:
Non-centrosymmetric materials that can be polarized under applied mechanical stress or electric field are piezoelectric in nature and the phenomenon is called piezoelectric effect. They are broadly classified as direct and converse piezoelectric effects. Piezo-ceramics have a wide range of applications such as piezoelectric actuators, sensors, and transducers. Among piezoceramics, ferroelectric based materials are imperative owing to the existence of spontaneous polarization in these systems. Several materials are investigated starting from naturally occurring crystals to synthetic ceramics but are limited in their application range. The piezoelectric and ferroelectrics properties of the solid-solutions based on lead zirconate and lead titanate called lead zirconate titanate (PZT), lead magnesium niobate-lead titanate (PMN-PT), lead zinc niobate-lead titanate (PZN-PT) (near morphotrophic phase boundary (MPB))
demonstrate their potential for myriad device applications besides inciting a great deal of academic interest. They have been widely used for commercial applications such as ultra sound transducers, ultrasonic motors, fuel injector actuators, nano positioners in scanning electron microscope etc. However, these materials contain more than 60% lead by weight and volatization of Pb at higher temperature, and disposal of lead results in environmental pollution and are fatal to human health. This gave an insight to search for lead-free solid solutions covering a wide spectrum of applications akin to that of PZT. The search for alternatives to lead based piezoelectric materials is now being focused on modified barium titanates and alkali niobates in which the incidence of MPB was reported similar to that of PZT. In this thesis the results pertaining to the various investigations carried out on modified barium titanates, Ba(Zr0.2Ti0.8)O3- x(Ba0.7Ca0.3)TiO3(BCZT), and alkali niobates, potassium sodium niobate (KNN), are presented.
Especially, lead-free piezoelectric material Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3(BCZT) with x= 0.5 has attracted great attention due to its excellent piezoelectric properties. Contrary to the other Pb-free systems, the BZT–BCT phase diagram shows a Morphotropic Phase Boundary (MPB) characterized by the existence of a tri-critical point (TCP), which is also the case for PZT and PMN–PT. One drawback of the BZT–xBCT (x=0.5) is its high sintering temperature (where it exhibits the largest d33 of 550 – 620pC/N). Several methods have been adopted and various additives are being added to bring down the sintering temperature, since high d33 requires an optimized sintering temperature of around 1540oC which also shows excellent ferroelectric properties. However, the methods that were reported in the literature to synthesize the above materials do not guarantee compositional homogeneity and also there is a limitation in obtaining ceramics of enhanced grain size as the ceramics comprising larger grains are demonstrated to exhibit high piezoelectric coefficients. Therefore to address these issues, the simple soft chemical route was adopted to synthesize chemically homogenous powder and the influence of microstructure (grain size) and ferroelectric domains on piezoelectric properties of the BCZT at nano and micron sized crystallites was studied. The results obtained are classified into chapter 3 and chapter 4 accordingly apart from introduction, materials, and methods. Another challenging area of research in lead free piezoceramics for nanoscale device application is to synthesize materials and to visualize the piezoelectric properties at nanoscale with controlled shapes and sizes. For that, Mg2+ ion was chosen as the dopant especially on Ba2+ sites to synthesize
Ba0.95Mg0.05Zr0.1Ti0.9O3 (BMZT) nanocrystals, as MgO is known to be an effective grain growth inhibitor in many functional and structural ceramics. Therefore in the present thesis Mg2+ ion was chosen to exercise a strict control over the grain size. The results obtained from this title compound are discussed in chapter 5.
Another class of material is K0.5Na0.5NbO3 (KNN), which has been considered a good candidate for lead-free piezoelectric materials. KNN exhibits an MPB around 50% K and 50% Na separating two orthorhombic phases from the complete solid solution of NaNbO3 (Anti-ferroelectric) and KNbO3 (ferroelectric). The major problem associated with KNN ceramic is its complex densification process; difficulty in processing and volatilization of sodium at higher sintering temperature leading to stoichiometric discrepancy. To overcome these difficulties, in the present investigations, an attempt has been made to fabricate KNN ceramics by employing the liquid phase sintering method. In this chapter, B2O3 and borate based glass (0.5 Li2O - 0.5K2O- 2B2O3) were chosen to improve the densification, grain size and their effects on the physical properties of the KNN ceramics are discussed in chapter 6. In chapter 7, KNN crystallites (with size varying from nano to micrometers) were dispersed in the Polyvinylidene fluoride (PVDF) matrix to obtain a polymer/nano or micro crystal composites and the effect of nano and micron sized KNN fillers on the structural, dielectric and piezoelectric properties were investigated. The results obtained pertaining to these aforementioned investigations are organized as follows.
In Chapter 1, a brief introduction to the field of ferroelectricity, piezoelectricity, and piezoelectric materials. The emphasis has been on the ferroelectric based piezoelectric materials belonging to the perovskite family of oxides. A brief exposure to the conventional lead based piezoceramics, lead zirconate titanate (PZT) is discussed. Furthermore, drawbacks associated with lead based ceramics are highlighted and alternatives to PZT based ceramics such as modified barium titanate and alkali niobate solid solutions are focused, leading to the motivation and objectives of our work.
Chapter 2 describes the various experimental techniques that are employed to synthesize and characterize the materials under investigation.
Chapter 3 deals with details concerning the characterization of Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) nanocrystals prepared via complex oxalate precursor route at a relatively low temperature (800°C/5h). The phase formation temperature of BCZT at nanoscale was confirmed by thermogravimetric (TG), differential thermal analysis (DTA) followed by X-ray powder diffraction (XRD) studies. Fourier Transform Infrared (FTIR) spectroscopy was carried out to confirm the complete decomposition of oxalate precursor into BCZT phase. The XRD and profile fitting revealed the coexistence of cubic and tetragonal phases and was also corroborated by Raman study. Transmission electron microscopy (TEM) studies carried out at 800°C and 1000°C/5h heat treated BCZT powder revealed the crystallite size to be in the range of 20 – 50 nm and 40 – 200 nm respectively. The optical band gap for BCZT nanocrystalline powder was obtained using Kubelka Munk function and was found to be around 3.12 ± 0.02 eV and 3.03± 0.02 eV respectively for 800°C (20 – 50 nm) and 1000°C/5h (40 – 200 nm) heat treated samples. The piezoelectric properties were studied for two different crystallite sizes (30 and 70 nm) using piezoresponse force microscope (PFM). The d33 coefficients obtained for 30 nm and 70 nm sized crystallites were 4 pm/V and 47 pm/V respectively. These were superior to those of BaTiO3 nanocrystal (≈ 50 nm) and promising from the technological/industrial applications perspective.
Chapter 4 deals with the studies concerning the effect of microstructure (Grain size) and ferroelectric domains on physical properties of Ba0.85Ca0.15Zr0.1Ti0.9O3 ceramics. Fine powders comprising nanocrystallites of Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) were synthesized via oxalate precursor method which facilitated to obtain homogenous and large grain sized ceramics at a lower sintering temperature. The compacted powders were sintered at various temperatures in the range of 1200°C - 1500°C for an optimized duration of 10h. Interestingly the one that was sintered at 1450°C/10h exhibited well resolved Morphotrophic Phase Boundary (MPB). The average grain size associated with this sample was 30 µm accompanied by higher domain density mostly with 90° twinning. These were believed to make a significant contribution towards obtaining large strain of about 0.2 % and piezoelectric coefficient as high as 563 pC/N. The maximum force that was generated by BCZT ceramic (having 30 µm grain size) was found to be 161 MPa which is much higher than that of known actuator materials such as PZT (40 MPa) and NKN-5-LT (7 MPa).
Chapter 5 reports the details involving the synthesis, structural, optical, and piezoelectric response of lead free Ba0.95Mg0.05Zr0.1Ti0.9O3 nanocrystalline powder. Nanocrystalline powders of Ba1-xMgxZr0.1Ti0.9O3 (x=0.025 - 0.1) were synthesized via citrate assisted sol-gel method. Interestingly, the one with x=0.05 in the system Ba1-xMgxZr0.1Ti0.9O3 exhibited fairly good piezoelectric response apart from the other physical properties. The phase and structural confirmation of synthesized powder was established by X-ray powder diffraction (XRD) and Raman Spectroscopic techniques. Two distinct Raman bands i.e., 303 cm-1 and 723 cm-1 characteristic of the tetragonal phase were observed. Thermogravimetric analysis (TGA) was performed to evaluate the phase decomposition of the as-synthesized Ba0.95Mg0.05Zr0.1Ti0.9O3 sample as a function of temperature. The average crystallite size associated with Ba0.95Mg0.05Zr0.1Ti0.9O3 was calculated using Scherrer formula based on the XRD data and was found to be 25 nm. However, Scanning and Transmission Electron Microscopy studies revealed the average crystallite size to be in the range of 30-40 nm. Kubelka-Munk function was employed to determine the optical band gap of these nanocrystallites. The piezoelectric response of 26 pm/V was observed for Ba0.95Mg0.05Zr0.1Ti0.9O3 nanocrystal by Piezoresponse Force Microscopy (PFM) technique. Photoluminescence (PL) study carried out on these nanocrystals exhibited a blue emission (470 nm) at room temperature.
Chapter 6 describes the effect of the addition of B2O3 on the density, microstructure, dielectric, piezoelectric and ferroelectric properties of K0.5Na0.5NbO3 ceramics. Boron oxide (B2O3) addition to pre-reacted K0.5Na0.5NbO3 (KNN) powders facilitated swift densification at relatively low sintering temperatures which was believed to be a key to minimize potassium and sodium loss. The base KNN powder was synthesized via solid-state reaction route. The different amounts (0.1 to 1 wt %) of B2O3 were added, and ceramics were sintered at different temperatures and durations to optimize the amount of B2O3 needed to obtain KNN pellets with the highest possible density and grain size. The 0.1 wt% B2O3 added KNN ceramics sintered at 1100°C for 7h exhibited higher density (98%) with grain size of ~5 µm. Scanning electron microscopy (SEM) studies confirmed an increase in average grain size with increasing B2O3 content at the appropriate temperature of sintering and duration.
The B2O3 added KNN ceramics exhibited improved dielectric and piezoelectric properties at room temperature. For instance, 0.1 wt% B2O3 added KNN ceramic exhibited d33 value of 116 pC/N which is much higher than that of pure KNN ceramics. Interestingly, all the B2O3 added (0.1 to 1wt %) KNN ceramics exhibited polarization – electric field (P vs E) hysteresis loops at room temperature. The remnant polarization (Pr) and coercive field (Ec) values are dependent on the B2O3 content and crystallite size. The details pertaining to the effect of the addition of borate based glass (0.5 Li2O - 0.5K2O- 2B2O3) on the physical properties of K0.5Na0.5NbO3 ceramics are also reported in this chapter. The addition of powdered 0.5 Li2O - 0.5K2O- 2B2O3 (LKBO) glass (0.5 to 2 wt%) to potassium sodium niobate, K0.5Na0.5NbO3 (KNN) powder facilitated higher densification which resulted in improved physical properties that include dielectric, piezoelectric and ferroelectric. The required polycrystalline powders of KNN were synthesized through solid-state reaction route, while LKBO glass was obtained via the conventional melt-quenching technique. Pulverized glass was added to KNN powders in different wt% and compacted at room temperature and these were sintered around 1100°C. Indeed the addition of optimum amount (1 wt %) of LKBO glass to KNN ceramics facilitated lowering of sintering temperature accompanied by larger grains (8 µm) with improved density. The dielectric constant (εr) measured at room temperature was 475 (at 10 kHz), whereas it was only 199 for the LKBO glass free KNN. The piezoelectric coefficient (d33) was found to be 130 pC/N for 1wt% LKBO added glass, which was much higher than that of pure KNN ceramics (85 pC/N). Indeed, the LKBO glass added samples did exhibit well saturated P versus E hysteresis loops at room temperature. Though there was no particular trend observed in the variation of Pr with the increase in glass content, the Pr values were higher than those obtained for KNN ceramics. The improved physical properties of KNN ceramics encountered in these studies were primarily attributed to enhancement in density and grain size.
Chapter 7 presents a comparative study on the structural, dielectric and piezoelectric properties of nano and micron sized K0.5Na0.5NbO3 fillers in PVDF composites. Polymer nanocrystal composites were fabricated by embedding polyvinylidene fluoride (PVDF) with different vol% of K0.5Na0.5NbO3 (KNN) nanocrystallites using hot-pressing technique. For comparison, PVDF-KNN microcrystal composites of the same compositions were also fabricated which facilitated the crystallite size (wide range) effect studies on the dielectric and piezoelectric properties. The structural, morphological, dielectric, and piezoelectric properties of these nano and micro crystal composites were investigated. The incorporation of KNN fillers in PVDF at both nano and micrometer scale above 10vol% resulted in the formation of polar β-form of PVDF. The room temperature dielectric constant as high as 3273 at 100Hz was obtained for PVDF comprising 40 vol% KNN nanocrystallites due to dipole –dipole interactions (as the presence of β-PVDF is prominent), whereas it was only 236 for PVDF containing the same amount (40 vol%) of micron sized crystallites of KNN at the same frequency. Various theoretical models were employed to predict the dielectric constants of the PVDF-KNN nano and microcrystal composites. PVDF comprising 70 vol% micronmeter sized crystallites of KNN exhibited d33 value of 35pC/N, while the nanocrystal composites of PVDF-KNN did not exhibit any piezoelectric response perhaps due to unrelieved internal stress within each grain besides having less number of domain walls.
The Thesis ends with summary and conclusions, though each chapter is provided with conclusions and a complete list of references.