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Duan, Runrun. "High Curie Temperature Bismuth- and Indium- Substituted Lead Titanate." Thesis, Available online, Georgia Institute of Technology, 2004:, 2004. http://etd.gatech.edu/theses/available/etd-06082004-124159/unrestricted/Duan%5FRunrun%5F200407%5Fmast.pdf.
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Thesis (M.S.)--School of Materials Science and Engineering, Georgia Institute of Technology, 2005. Directed by Robert Snyder.Shrout, Thomas, Committee Member ; Snyder, Robert, Committee Member ; Speyer, Robert, Committee Chair. Includes bibliographical references.
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Khan, Ashraf Reza. "Preparation and characterization of lead lanthanum titanate thin films by metalorganic decomposition." Thesis, Virginia Tech, 1994. http://hdl.handle.net/10919/42122.
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There is a critical need for materials with very high dielectric constant to be integrated in the next generation of 64- and 256-Mb ULSI DRAMs. Materials in the Pb-based perovskite family have high relative permittivities and have consequently attracted a world wide attention. Cubic Lead Lanthanum Titanate (PLT) is one of the prime candidates in this respect and its structure and properties in the thin film form were investigated in the present study, for potential application in the ULSI DRAMs.
Thin films of Lead Lanthanum Titanate corresponding to 28 atomic percentage of lanthanum were prepared by metalorganic decomposition (MOD) process. Solutions were prepared from lead acetate, lanthanum acetate and titanium iso-propoxide and thin films were then spin-coated from these solutions on PtlTilSi02/Si and sapphire substrates. The films were fabricated from two solutions of different compositions. The composition of the first solution was determined assuming that the incorporation of La3+ in the PbTi03 structure gives rise to A-site or Pb vacancies whereas for the composition of the other solution the creation of B-site or Ti vacancies was assumed. The effect of excess lead on the structure and the properties was also studied for 0% to 20% of excess PbO. The x-ray diffraction patterns of all films at room temperature indicated a cubic structure with lattice constant of 3.92 A. Optical and electrical measurements showed that the films made assuming B-site vacancies had better properties. In general, excess PbO was found to improve the optical as well as the electrical properties of films. However, in films with Bsite vacancies this improvement occurred only up to 5-10% of excess PbO, while higher PbO additions had a deleterious effect. The films had high resistivity, good relative permittivity, low loss, very low leakage current density, and high charge storage density. A type-B film with 10 % excess Pb had a permittivity of 1336 at 100 kHz. It also had a charge storage density at room temperature of around 16.1 μC/cm2 at a field of 200 kV/cm and no sign of polarization loss or breakdown was observed up to 1010 cycles under the accelerated degradation breakdown test.
Master of Science
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Jeddy, Shehnaz. "Thermal stability of defects in strontium titante [i.e., titanate] susbtrates for multiferroic materials." Birmingham, Ala. : University of Alabama at Birmingham, 2008. https://www.mhsl.uab.edu/dt/2008m/jeddy.pdf.
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Sun, Jingyu. "Carbon nanotube growth on perovskite substrates." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:2b77fe9b-7313-49b2-b490-70574b4af565.
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This thesis reports on the chemical vapour deposition (CVD) growth of carbon nanostructures (mainly carbon nanotubes (CNTs)) on perovskite oxide surfaces with the aid of various catalysts. Two types of perovskite oxide, single crystal SrTiO3 (001) and polycrystalline BaSrTiO3, have been used as catalyst supports (in metal-catalyst-involved CVD routes) or as catalysts (via metal-catalyst-free CVD routes) for the growth of carbon nanostructures. In metal-catalyst-involved cases, SrTiO3 (001) single crystal has been proven, for the first time, to serve as a substrate for the growth of CNTs. Fe and Ni catalysts can be tailored in a controllable manner on SrTiO3 (001) surfaces prior to the CNT synthesis, forming truncated pyramid shaped nanocrystals with uniform size distributions. The growth of vertically aligned CNT carpets was realised with the aid of Fe on SrTiO3 (001) surfaces, and it was further found that the CNTs grow via a base growth model. Furthermore, it is possible to grow helical carbon nanostructures on BaSrTiO3 substrates by introducing a Sn catalyst into the system. The synthesised helical carbon nanostructures follow a tip growth mode, where the structural and chemical aspects of catalyst particles gave rise to a wide range of carbon morphologies. CNTs were also grown on single crystal SrTiO3 (001) and polycrystalline BaSrTiO3 substrates via metal-catalyst-free routes. The surface-roughness-tailored growth of CNTs was surprisingly achieved on a series of engineered SrTiO3 (001) surfaces, where a correlation between the surface roughness/morphology of the substrates and the relevant catalytic activity was revealed. The growth of CNTs arises because the catalyst fabrication methods lead to the formation of SrTiO3 asperities with nanoscale curvatures, over which the CNTs are generated throughout a lift-off process. Facet-selective growth of CNTs was observed on polycrystalline BaSrTiO3 surfaces, where BaSrTiO3 (110) facets lead to the growth of CNTs on them, whereas the (001) facets result in no growth at all. This observation was further analysed in the content of the adsorption and diffusion of carbon species on distinct BaSrTiO3 facets, before reaching the conclusion that the formation of CNTs occurs through a metal-free, stack-up process driven by the assembly of the carbon fragments.
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Zhang, Qingteng. "Properties of Ferroelectric Perovskite Structures under Non-equilibrium Conditions." Scholar Commons, 2012. http://scholarcommons.usf.edu/etd/4422.
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Ferroelectric materials have received lots of attention thanks to their intriguing properties such as the piezoelectric and pyroelectric effects, as well as the large dielectric constants and the spontaneous polarization which can potentially be used for information storage. In particular, perovskite crystal has a very simple unit cell structure yet a very rich phase transition diagram, which makes it one of the most intensively studied ferroelectric materials. In this dissertation, we use effective Hamiltonian, a first-principles-based computational technique to study the finite-temperature properties of ferroelectric perovskites. We studied temperature-graded
(BaxSr1-x )TiO3 (BST) bulk alloys as well as the dynamics of nanodomain walls (nanowalls) in Pb(ZrxTi1-x )O3 (PZT) ultra-thin films under the driving force of an AC field. Our computations suggest that, for the temperature-graded BST, the polarization responds to the temperature gradient (TG), with the "up" and "down" offset observed in polarization components along the direction of TG, in agreement with the findings from experiments. For the nanowalls in PZT, the dynamics can be described by the damped-harmonic-oscillator model, and we observed a size-driven transition from resonance to relaxational dynamics at a critical thickness of 7.2 nm. The transition originates from the change in the effective mass of a nanowall as a film thickness increases. Some of the findings may find potential applications in various devices, such as thermal sensors, energy converters, or novel memory units.
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AZEVEDO, Sérgio Alves de. "Óxidos cerâmicos a base de SrTiO3 e substituídos com Ferro/Prata – Caracterização Estrutural." Universidade Federal do Maranhão, 2015. http://tedebc.ufma.br:8080/jspui/handle/tede/1805.
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Strontium titanate, SrTiO3 (ST) is a mixed oxide from the group of perovskites, has a cubic structure and a band gap of 3.2 eV. In this study systems SrTiO3(ST), SrTi0,90Fe0,10O3(STF), Sr0,90Ag0,10TiO3(SAT) and Sr0,95Ag0,05Ti0,90Fe0,10O3(SATF) were synthesized by the Pechini method in which the same, favor the production of nanostructured materials with a high stoichiometric accordingly. The precursors used were titanium isopropoxide, citric acid, strontium nitrate, ferric nitrate, silver nitrate and ethylene glycol. For the formation of the precursor powder, the resin is calcined at 300 °C for 1 hour with a ramp of 10 °C min-1. The precursor powder was characterized by TG/DTA. For the formation of calcined systems we used different temperatures of 400 °C / 500 °C/ 600 °C/ 700 °C/ 2h with a ramp of 10 °C min-1. The sample composition was calcined in ST 550 °C/ 2h to examine the formation of the phase. The samples were characterized by X-Ray Diffraction (XRD) spectroscopy, FTIR, UV-Vis spectroscopy, Raman spectroscopy and B.E.T. the sample STF showed a peak shift DTA higher intensity to lower temperature, resulting in a more rapid decomposition. The x-ray diffractograms show the formation of perovskite phase at low temperature of 600 °C with secondary phase SrCO3 and TiO2, the SAT and SATF samples occurred and formation of metal pranta as a secondary phase. Infrared spectra show that the material exhibits short-range organization and having SrCO3 as a secondary phase. Raman spectra show first order band which is characteristic of tetragonal structure ST. The samples are mesoporous, the substitution Ti / Fe and Sr / Ag promoted the reduction of the surface area of the samples. The addition of iron as a substituent ST caused a reduction of the optical band gap 3.21(2) to 2.31(2) in PBS and 2.16(1) composition in SATF composition. It can be concluded that the method is efficient in the synthesis of structural organization samples with short and long range, using calcination temperatures above 600 °C, and that the substitution by Ti/Fe promotes the reduction of the band gap and the surface area of the ST.
O Titanato de estrôncio, SrTiO3 (ST) é um óxido misto do grupo das perovskitas, apresenta estrutura cúbica e um “band gap” de 3,2 eV. Neste estudo, os sistemas SrTiO3(ST), SrTi0,90Fe0,10O3(STF), Sr0,90Ag0,10TiO3(SAT) e Sr0,95Ag0,05Ti0,90Fe0,10O3(SATF) foram sintetizados pelo método Pechini, o mesmo favorece a obtenção de materiais com alta conformidade estequiométrica. Os precursores utilizados foram: isopropóxido de titânio, ácido cítrico, nitrato de estrôncio, nitrato férrico, nitrato de prata e etileno glicol. Para a formação do pó precursor, calcinou-se a resina a 300ºC por 1 hora com rampa de 10 ºC.min-1. O pó precursor foi caracterizado por TG/DTA. Para a formação dos sistemas calcinados utilizou-se diferentes temperaturas de 400 ºC/500 ºC/600 ºC/700 ºC/2h com rampa de 10 ºC.min-1. A amostra com composição ST foi calcinada em 550 ºC/2h para analisar a formação da fase. As amostras foram caracterizadas por Difração de Raios-X (DRX), Espectroscopia FTIR, Espectroscopia UV-VIS, Espectroscopia Raman e B.E.T. A amostra STF apresentou um deslocamento do pico DTA de maior intensidade, para temperatura menor, resultando em uma decomposição mais rápida. Os difratogramas de Raios-x comprovam a formação da fase perovskita a partir da temperatura de 600ºC, com fase secundaria de SrCO3 e TiO2, nas amostras SAT e SATF ocorreu e formação de pranta metálica como fase secundaria. Os espectros infravermelhos mostram que o material apresenta organização a curto alcance e que apresenta SrCO3 como fase secundária. Os espectros Raman apresentam banda de primeira ordem que é característico da fase tetragonal da estrutura ST. As amostras são mesoporosas, as substituições Ti/Fe e Sr/Ag promoveram a redução da área superficial das amostras. A adição de ferro como substituinte promoveu a redução do band gap óptico do ST de 3,21(2) para 2,31(2) na composição STF e 2,16(1) na composição SATF. Pode se concluir que o método é eficiente na síntese das amostras com organização estrutural a curto e longo alcance, utilizando temperaturas de calcinação acima de 600 ºC, e que a substituição Ti por Fe promove a redução do “band gap” e da área superficial do ST.
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Behnke, Matthew. "INVESTIGATION OF YTTRIUM TITANATE IN A LEAD IODIDE PEROVSKITE SENSITIZED SOLAR CELL TO ENHANCE EFFICIENCY." OpenSIUC, 2015. https://opensiuc.lib.siu.edu/theses/1814.
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AN ABSTRACT OF THE THESIS OF MATTHEW BEHNKE, for the Master of Science degree in Mechanical Engineering, presented on November 3rd, 2015, at Southern Illinois University Carbondale TITLE: INVESTIGATION OF YTTRIUM TITANATE IN A LEAD IODIDE PEROVSKITE SENSITIZED SOLAR CELL TO ENHANCE EFFICIENCY MAJOR PROFESSOR: Dr. Kanchan Mondal This research is aimed to evaluate the effects of a pyrochlore to enhance the efficiency of a solid state organic inorganic halide-sensitized solar cell. The objectives of this study are to synthesize, assemble, test, and evaluate a pyrochlore that will lower the band gap of TiO2 and increase conversion efficiency in solid state organic-inorganic halide sensitized solar cells. The cells that were constructed and evaluated were made up of titanium oxide (TiO2) or yttrium titanate (Y2Ti2O7), a perovskite organic lead iodide (CH3NH3PbI3) as the polymer, a hole transport membrane (HTM) made of 1,3,5-Tris(diphenylamino) benzene, a layer of carbon black, and Indium Tin Oxide (ITO) coated glass. The cells were characterized and tested under a 658 nm wavelength light with a power density of 65 mW/cm2 , while the individual substances were examined under a scanning electron microscope and transmission electron microscopes and x-ray diffraction analyses were conducted to determine the structural make up of the individual materials. From the obtained data cell conversion efficiencies and fill factors were calculated. It was found that the Y2Ti2O7 nanofiber based cells exhibited the highest fill factor of 0.57 compared to 0.20 -0.29 obtained during the experiments with TiO2 based cells. The cell efficiencies of the Y2Ti2O7 were however low probably due to a significant portion of amorphous material in the photoactive layer of the cell.
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Sakaguchi, Tatsunori. "Synthesis and Characterization of Titanium Perovskite Oxyhydrides Prepared by Topochemical Hydride Reduction." 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/215561.
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Kaspar, Tiffany C. "Materials and magnetic studies of cobalt-doped anatase titanium dioxide and perovskite strontium titanate as potential dilute magnetic semiconductors /." Thesis, Connect to this title online; UW restricted, 2004. http://hdl.handle.net/1773/9902.
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Lavinscky, Anderson Borges da Silva. "Síntese e caracterização do sistema SrTi1-xSnxO3 na forma de pó e na forma de filmes finos para aplicação como sensores de gases tóxicos." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/18/18158/tde-15022019-085246/.
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O objetivo desta tese de doutorado foi estudar a influência da adição do íon estanho (Sn4+) à rede do composto SrTiO3 em substituição ao íon de titânio visando otimizar as propriedades elétricas desse composto e, como consequência, obter uma melhora de seu desempenho como um sensor de gás na forma de filmes finos. Para realizar a deposição destes filmes finos através dos métodos de Deposição por Feixe de Elétrons (EBD), alvos cerâmicos de composição SrTi1-xSnxO3 (STSO) com x = 0; 0,20; 0,40; 0,60; 0,80; 0,85; 0,90; 0,95; 1 foram obtidos através do método dos precursores poliméricos modificado. A sequência de formação de soluções sólidas foi determinada através do refinamento Rietveld das amostras STSO na forma de pó sinterizadas, obtidas através dos métodos dos precursores poliméricos e de reação de estado sólido, mostrando que a transição da fase cúbica Pm3̄m do composto SrTiO3 até a fase ortorrômbica Pnma do composto SrSnO3 não depende do método de síntese. As medidas de espectroscopia Raman e absorção de raios-X (XANES, na borda K do Ti) das amostras tanto na forma de pó, obtidas através do método dos precursores poliméricos e de reação de estado sólido, quanto na forma de filme fino obtidas por EBD revelaram a existência de uma desordem local na rede do composto SrTiO3 que diminui com o aumento da temperatura e com a diminuição da concentração de Sn. Os filmes finos STSO obtidos por EBD foram avaliados como sensores utilizando-se os gases O3 e NH3. Em medidas realizadas com o gás ozônio (O3), os resultados mostraram que os filmes finos de 100 nm de espessura apresentaram uma maior sensibilidade tendo a amostra com 60% de Sn com o melhor desempenho a 350°C para 0,15 ppm do gás. As análises de performance dos filmes STSO quanto a seletividade indicaram que não foram seletivos e que apresentaram uma maior resposta ao gás ozônio quando comparados ao gás NH3.The objective of this work was to study the influence of the addition of tin ion (Sn4+) into the SrTiO3 compound lattice, to replace the titanium ion (Ti4+). The aim was to optimize the electrical properties of SrTiO3 compound and, as a consequence, to obtain an improvement of its performance as a gas sensor in the thin films samples. To perform the deposition of these thin films through Electron Beam Deposition (EBD), ceramic targets of composition SrTi1-xSnxO3 (STSO) with x = 0; 0.20; 0.40; 0.60; 0.80; 0.85; 0.90; 0.95; and 1 were obtained by the modified polymer precursor method. The solid solution formation sequence was determined by the Rietveld refinement of the STSO sintered powdered samples, obtained by both polymeric precursor and solid-state reaction methods, showing that the transition from the cubic Pm3̄m phase of the SrTiO3 compound to the orthorhombic Pnma phase of the SrSnO3 compound does not depend on the synthesis method. The measurements of Raman spectroscopy and absorption of X-rays (XANES, at Ti K-edge), of the powdered samples obtained by both synthesis methods and of the thin films obtained by EBD, revealed the existence of a local disorder in the SrTiO3 compound lattice which decreases with increasing of temperature and with decreasing of Sn concentration. The STSO thin films were evaluated as sensors using the O3 and NH3 gases. In measurements accomplished with the ozone gas (O3), the results showed that thin films of 100 nm thickness had a higher sensitivity. The sample having 60% of tin showed the best performance at 350°C for 0.15 ppm of ozone gas. The performance analysis related to the selectivity of the STSO films indicated they were not selective and that presented a higher response to the ozone gas when compared to the NH3 gas.
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Goble, Nicholas James. "ELECTRONIC TRANSPORT AT SEMICONDUCTOR AND PEROVSKITE OXIDE INTERFACES." Case Western Reserve University School of Graduate Studies / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=case1454002713.
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Nadouf, Mohammed. "Synthese et etude de poudres submicroniques de titanate de baryum et de ses solutions solides avec le strontium." Université Louis Pasteur (Strasbourg) (1971-2008), 1986. http://www.theses.fr/1986STR13129.
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On etudie les solutions solides entre titanate de baryum et titanate de strontium. Deux methodes de synthese de ces perovskites sont abordees : la methode ceramique classique, ou l'on fait reagir des solides a haute temperature, et la methode oxalique qui fait intervenir la preparation d'un sel mixte que l'on decompose a basse temperature. Les relations entre la nature des sels des oxydes, le ph de precipitation, la temperature de reaction ou de precipitation et les caracteristiques structurales et proprietes physiques des ceramiques frittees sont etudiees
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Ernst, Eric Michael. "Hydrothermal conversion of diatom frustules into barium titanate based replicas." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/24687.
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Thesis (M. S.)--Materials Science and Engineering, Georgia Institute of Technology, 2008.Committee Chair: Sandhage, Kenneth H.; Committee Co-Chair: Snyder, Robert L.; Committee Member: Sanders, Thomas H.
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Aljaberi, Ahmed D. A. "Development and characterisation of an A-site deficient perovskite as alternative anode material for solid oxide fuel cells." Thesis, University of St Andrews, 2013. http://hdl.handle.net/10023/3690.
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The research presented in this thesis is a collection of many different, yet connected, parts that stemmed from the development of a new alternative material intended to be utilised as anode material in solid oxide fuel cells. The main part is the research conducted in the development and characterisation of the novel A-site deficient La₀.2₂Sr₀.₇₋ₓCaₓTiO₃. Calcium introduction resulted in reducing this perovskite unit cell volume which, at the beginning, enhanced its electrical conductivity in reducing conditions. However, the ideal cubic symmetry coud not be maintained, as in the starting material LA₀.₂Sr₀.₇TiO₃, as a result of the increased A-site ionic radius mismatch and two lower symmetries were observed at room temperature. These were the tetragonal I4/mcm for 0.1 ≤ x ≤ 0.35 and orthorhombic Pbnm for 0.4 ≤ x ≤ 0.7. Higher temperature NPD data showed that the orthorhombic samples transformed into higher symmetries with Pbnm → I4/mcm → Pm3-m phase transitions. Detailed crystallographic analysis is discussed; where the different unit cells showed changes to the tilts of the BO₆ octahedra, along with distortions to these octahedra. DC conductivity measurements showed a high electrical conductivity of 27.5 S/cm for a pre-reduced composition La₀.₂Sr₀.₂₅Ca₀.₄₅TiO₃ at 900°C and pO₂ = 10⁻¹⁹ atm. This material showed very encouraging features; which makes it a very promising anode material for SOFCs. A study was also done which explores the best renewable energy options for the United Arab Emirates given its local climate and other aspects. The reliance on seawater desalination is argued to by unsustainable for different reasons. Thus, water security should be a main element in the planning process for adopting renewable energy technologies. A system that combines different technologies; with a focus on fuel cells technology; is outlined which is thought of to be a very promising basis for a broader system that will secure power and water in a very environment friendly way. Different compositions of the system La₀.₂Sr₀.₇₋ₓCaₓTiO₃ were also studied using AC impedance spectroscopy in order to establish whether or not this system can show a ferroelectric behaviour. Results showed a variation in the dielectric constant of different samples with temperature; however, no Curie point was observed. Nonetheless, the results did show that the different compositions were very homogeneous when fully oxygenated and there were some indications of possible symmetry changes at sub-ambient temperatures. The final part of this thesis outlined the work done towards the development of a new analytical instrument. An existing TGA instrument was altered in order to provide a simultaneous thermogravimetric analysis and DC conductivity measurement for solid solutions at controlled temperature and oxygen partial pressure. Results were obtained for different samples of the system La₀.₂Sr₀.₇₋ₓCaₓTiO₃ which showed a great dependence of the electrical conductivity on the oxygen stoichiometry in these oxides. Also, a direct method is possible with this instrument to estimate the oxygen chemical diffusion coefficient using the electrical conductivity relaxation method. This new setup will be very useful for different electrochemical and thermal studies which can broaden the understanding of the different mechanisms that affect the performance of different solid state materials.
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Laurent, Marie-José. "Physico-chimie du frittage basse temperature d'un materiau dielectrique de type iii a base de titanate de strontium dope." Caen, 1988. http://www.theses.fr/1988CAEN2008.
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On propose de preparer un materiau a haute constante dielectrique a couches d'arret aux joints de grains par un frittage a basse temperature (1100**(o)c) de srtio::(3) dope et reduit en presence d'un sel de lithium. La formation de la seconde phase isolante constituee de bi::(2)o::(3) est envisagee au cours de ce meme cycle thermique. La poudre de srtio::(3) est prealablement dopee par des composes de structure perovskite afin de faciliter l'incorporation du dopant, et reduite a 1350**(o)c sous atmosphere reductrice. La physico-chimie de frittage a 1100**(o)c en presence d'un sel de lithium et les proprietes dielectriques et microstructurales de srtio::(3) dope par srli::(1/4)nb::(3/4)o::(3) d'une part, la::(2/3)tio::(3-epsilon ) d'autre part, sont etudiees puis comparees a celles de srtio::(3) dope par la la::(2)o::(3) et srtio::(3) non dope
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Barnes, Paris W. "Exploring structural changes and distortions in quaternary perovskites and defect pyrochlores using powder diffraction techniques." Columbus, Ohio : Ohio State University, 2003. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1064346592.
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Thesis (Ph. D.)--Ohio State University, 2003.Title from first page of PDF file. Document formatted into pages; contains xxvi, 255 p.; also includes graphics. Includes abstract and vita. Advisor: Patrick M. Woodward, Dept. of Chemistry. Includes bibliographical references (p. 221-228).
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Inglês, Daniella. "ESTRUTURA E PROPRIEDADES ÓPTICAS DO SISTEMA TITANATO-ESTANATO DE ESTRÔNCIO [Sr(Ti1-xSnx)O3 x = 0; 0,25; 0,50; 0,75; 1]." UNIVERSIDADE ESTADUAL DE PONTA GROSSA, 2013. http://tede2.uepg.br/jspui/handle/prefix/2109.
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Titanates have perovskite crystalline structure very known for electrical and optical properties used in the electronic devices such as sensors, capacitors, nonvolatile and dynamic random access memories. In particular, titanates structures are characterized for the ABO3 formula being A crystallographic site formed by 12 atoms neighbors and B crystallographic site formed by 6 atoms neighbors. However, researches about strontium titanate-stannate system are found minimally in the literature. Articles discussing synthesis, characterization and compositions are insufficiently presented. This project shows a theoretical study of the structure and optical properties of the strontium titanate-stannate system for different substitutions [Sr(Ti1-xSnx)O3 x = 0; 0,25; 0,50; 0,75; 1]. It was used theoretical-computational methodology based on, Density Functional Theory (DFT) with B3LYP functional to calculate the structure of the models SrTiO3 (STO), Sr(Ti1-xSnx)O3 (STS) and SrSnO3 (SSO). Theoretical data of parameter lattice, cell unit angles, volume, band gap, overlap population, charges and free energy are presented as well as analysis and discussion of the results for band structure (EB), density of states (DOS), electron density maps. Thus, one may present the data obtained and investigate the properties of the materials.
Titanatos possuem estrutura cristalina perovskita muito conhecida pelas propriedades elétricas e ópticas utilizadas em dispositivos eletrônicos como sensores, capacitores, memória de acesso randômico dinâmica e não volátil. Em particular, as estruturas de titanatos são caracterizadas pela fórmula ABO3 sendo A sítio cristalográfico formado por 12 átomos vizinhos e B o sítio cristalográfico formado por 6 átomos vizinhos. No entanto, pesquisas sobre o sistema titanato-estanato de estrôncio são encontradas minimamente na literatura. Artigos que discutem a síntese, caracterização e composições são insuficientemente apresentados. Este trabalho apresenta o estudo teórico da estrutura e propriedades ópticas do sistema titanato-estanato de estrôncio para diferentes substituições [Sr(Ti1-xSnx)O3 x = 0; 0,25; 0,50; 0,75; 1]. Utilizou-se metodologia teórico-computacional baseada em, Teoria do Funcional de Densidade (DFT) com funcional B3LYP, para cálculo da estrutura dos modelos SrTiO3 (STO), Sr(Ti1-xSnx)O3 (STS) e SrSnO3 (SSO). Dados teóricos de parâmetro de rede, ângulos da célula unitária, band gap, recobrimento populacional, cargas e energia livre são apresentados como também a análise e discussão dos resultados por meio de estrutura de bandas (EB), densidade de estados (DOS), mapas de densidade eletrônica. Desta forma, podem-se apresentar os dados obtidos e investigar as propriedades dos materiais.
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Köbernik, Gert. "Präparation und Charakterisierung ferroelektrischer perowskitischer Multilagen.: Preparation and electrical characterisation of multilayers of ferroelectric Perovskites." Doctoral thesis, Technische Universität Dresden, 2003. https://tud.qucosa.de/id/qucosa%3A24345.
Full textAbstract:
This work deals with the structural and dielectric properties of Bariumtitanate (BTO) / Strontiumtitanate (STO) superlattices. The investigations were carried during the research for a doctoral thesis on the IFW Dresden, Institute for Metallic Materials (under supervision of Prof. Schulz). These multilayers have been prepared on single crystalline STO of (100) and (111) orientated substrates. All films where grown in an epitaxial mode. Additional superlattices and Bariumstrontiumtitanate (BSTO) thin films on silicon substrates with platinum bottom electrodes have been prepared. Thereby, (111) fibre-textured polycrystalline superlattices were produced. According to our knowledge this result was achieved for the first time (is unique in the world at the moment). According to high resolution TEM investigations of (001) oriented superlattices multilayers with atomically thin interfaces without noticeable interdiffusion have been prepared. XRD pattern of a multilayer consisting of BTO and STO monolayers that have only a thickness adequate one unit cell of BTO respective STO confirm this assumption. Multilayers on (111) oriented STO substrates show a much higher interface roughness than (001) orientated films. Regarding to the examinations in this thesis it is suggested that the roughness is correlated with the reduction of internal stresses by deformation of the stack and not with interdiffusion between the monolayers. For electrical measurements the film thickness has been varied from 30 nm to 300 nm and the periodicity in the range from 0.8 nm to 20 nm. Additionally, BSTO films of equivalent thickness and integral chemical composition were produced. Dielectical measurements were carried out in the temperature range from 20 K to 600 K and hysteresis measurements were done. It has to be pointed out, that multilayers have always lower dielectrical performances then BSTO films. In all cases the dielectric constant (DC) decreases with decreasing film thickness. Multilayers of a small periodicity show the highest DC?s, decreasing with increasing monolayer thickness in all cases. The maximum of DC shifted with decreasing film thickness to higher temperatures thus correlating with an increase of the out of plane lattice parameter. In this paper the mismatch between the stack respectivly the BSTO layers and the substrate has widely been discussed. In the case of BSTO the dielectric data can be qualitatively explained with the theory of strained films, developed mainly by Pertsev, under the assumption of a strain gradient in the thin film. Strain effects do also play an important role in ferroelectric multilayers as well as size and coupling effects between the monolayers. An adequate theory for the description of the dielectric behaviour of the ferroelectric superlattice produced during this research does yet not exist. Some thesis where pointed out, which effects have to be essentially included in to a consistent theory of ferroelectric multilayer. Some practical tips are also given, how to prepare monolayers and superlattices with very high DC and exellent hysteretic behaviour.Es wurden (001) und (111) orientierte symmetrische BTO/STO-Multilagen auf niobdotierten STO-Einkristallen abgeschieden. Hierbei wurde sowohl die Gesamtschichtdicke, als auch deren Periodizität variiert. Zum Vergleich wurden weiterhin Ba0.5Sr0.5TiO3-Mischschichten unterschiedlicher Dicke präpariert. Aus den HRTEM und XRD Untersuchungen kann geschlossen werden, dass alle erhaltenen Schichten sowohl phasenrein als auch perfekt biaxial texturiert sind. Im Falle der (001) orientierten Multilagen konnten atomar scharfe Grenzflächen zwischen Einzellagen erhalten werden, wobei sich die Einzellagendicke bis auf eine Monolage (0.4 nm) reduzieren lässt. Aus der Schichtdickenabhängigkeit von d(001), dem mittleren out-of-plane Gitterparameter der Schicht, wird geschlossen, dass die Schichten auf den STO-Einkristallen Spannungsgradienten in den Schicht-normalen besitzen und an der Grenzfläche zum Substrat am stärksten verspannt sind. Die (111) orientierten Multilagen auf den STO-Einkristallen zeigen gegenüber den Schichten auf den (100) orientierten STO-Einkristallen eine deutlich erhöhte Interfacerauhigkeit. Vermutet wird, dass dies einerseits durch die andere kristallographische Orientierung der Wachstumsnormalen bedingt ist, weil damit jeweils keine geschlossenen SrO- bzw. BaO- und TiO3-Lagen ausgebildet werden. Andererseits zeigen die TEM-Aufnahmen eine deutliche Zunahme der Welligkeit der Einzellagen mit wachsendem Abstand vom Substrat, die rein mechanischen Effekten zugeschrieben wird. Die Verwölbung der Einzellagen könnte damit der Reduzierung der mechanischen Energie innerhalb des Systems dienen, wobei die Netzebenen dem Verlauf der Einzellagen folgen. Auf platinbeschichteten Siliziumsubstraten konnten erstmals phasenreine (111) fasertexturierte Mischschichten und BTO/STO-Multilagen abgeschieden werden. Grundlage hierfür war die Optimierung des Pt/Ti/SiO2/Si Schichtsystems hinsichtlich seiner thermischen Stabilität bis zu 800°C. Die Textur der Schichten wird von der Platingrundelektrode übernommen und deren Rauhigkeit teilweise verstärkt. Eine mechanische Verwölbung der Einzellagen konnte hier nicht beobachtet werden. Für die elektrischen Messungen wurden auf allen Schichten etwa 50 nm dicke Platinelektroden durch eine Hartmaske mittels Elektronenstrahlverdampfung im Hochvakuum bei etwa 300°C aufgebracht. Anschließend wurden die Schichten an Luft getempert, um das Sauerstoffdefizit, dass sich bei der Elektrodenabscheidung einstellt, auszugleichen. Die elektrischen Messungen zeichnen sich durch den sehr großen untersuchten Temperaturbereich aus. Temperaturabhängige Messungen im Bereich von 30-600 K finden sich für ferroelektrische Dünnschichten sehr selten in der Literatur und stellen für BTO/STO-Multilagen ein Novum dar. Auch die biasabhängige und teilweise auch temperaturabhängige Messung der Kapazität der Multilagen (C-V-Messungen) ist bisher einmalig. Durch die temperaturabhängigen Hysteresemessungen wurden Einblicke in den elektrischen Polungszustand der Schichten erhalten. Dadurch wird eine sinnvolle Interpretation der ε(T)-Kurven erst möglich. Der Vorteil der Integration des Polarisationsstromes unter Verwendung einer Dreieckspannung als Messsignal besteht in der direkten physikalischen Aussage der Strom-Spannungskurven über die Schaltspannung der Schichten.
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Harkins, Paula. "EELS and ELNES : investigation of titanate and zirconate perovskites." Thesis, University of Glasgow, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.425162.
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Ovalle, Alejandro. "Manganese titanium perovskites as anodes for solid oxide fuel cells." Thesis, St Andrews, 2008. http://hdl.handle.net/10023/567.
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Köbernik, Gert. "Präparation und Charakterisierung ferroelektrischer perowskitischer Multilagen." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2004. http://nbn-resolving.de/urn:nbn:de:swb:14-1088508748390-02540.
Full textAbstract:
This work deals with the structural and dielectric properties of Bariumtitanate (BTO) / Strontiumtitanate (STO) superlattices. The investigations were carried during the research for a doctoral thesis on the IFW Dresden, Institute for Metallic Materials (under supervision of Prof. Schulz). These multilayers have been prepared on single crystalline STO of (100) and (111) orientated substrates. All films where grown in an epitaxial mode. Additional superlattices and Bariumstrontiumtitanate (BSTO) thin films on silicon substrates with platinum bottom electrodes have been prepared. Thereby, (111) fibre-textured polycrystalline superlattices were produced. According to our knowledge this result was achieved for the first time (is unique in the world at the moment). According to high resolution TEM investigations of (001) oriented superlattices multilayers with atomically thin interfaces without noticeable interdiffusion have been prepared. XRD pattern of a multilayer consisting of BTO and STO monolayers that have only a thickness adequate one unit cell of BTO respective STO confirm this assumption. Multilayers on (111) oriented STO substrates show a much higher interface roughness than (001) orientated films. Regarding to the examinations in this thesis it is suggested that the roughness is correlated with the reduction of internal stresses by deformation of the stack and not with interdiffusion between the monolayers. For electrical measurements the film thickness has been varied from 30 nm to 300 nm and the periodicity in the range from 0.8 nm to 20 nm. Additionally, BSTO films of equivalent thickness and integral chemical composition were produced. Dielectical measurements were carried out in the temperature range from 20 K to 600 K and hysteresis measurements were done. It has to be pointed out, that multilayers have always lower dielectrical performances then BSTO films. In all cases the dielectric constant (DC) decreases with decreasing film thickness. Multilayers of a small periodicity show the highest DC?s, decreasing with increasing monolayer thickness in all cases. The maximum of DC shifted with decreasing film thickness to higher temperatures thus correlating with an increase of the out of plane lattice parameter. In this paper the mismatch between the stack respectivly the BSTO layers and the substrate has widely been discussed. In the case of BSTO the dielectric data can be qualitatively explained with the theory of strained films, developed mainly by Pertsev, under the assumption of a strain gradient in the thin film. Strain effects do also play an important role in ferroelectric multilayers as well as size and coupling effects between the monolayers. An adequate theory for the description of the dielectric behaviour of the ferroelectric superlattice produced during this research does yet not exist. Some thesis where pointed out, which effects have to be essentially included in to a consistent theory of ferroelectric multilayer. Some practical tips are also given, how to prepare monolayers and superlattices with very high DC and exellent hysteretic behaviourEs wurden (001) und (111) orientierte symmetrische BTO/STO-Multilagen auf niobdotierten STO-Einkristallen abgeschieden. Hierbei wurde sowohl die Gesamtschichtdicke, als auch deren Periodizität variiert. Zum Vergleich wurden weiterhin Ba0.5Sr0.5TiO3-Mischschichten unterschiedlicher Dicke präpariert. Aus den HRTEM und XRD Untersuchungen kann geschlossen werden, dass alle erhaltenen Schichten sowohl phasenrein als auch perfekt biaxial texturiert sind. Im Falle der (001) orientierten Multilagen konnten atomar scharfe Grenzflächen zwischen Einzellagen erhalten werden, wobei sich die Einzellagendicke bis auf eine Monolage (0.4 nm) reduzieren lässt. Aus der Schichtdickenabhängigkeit von d(001), dem mittleren out-of-plane Gitterparameter der Schicht, wird geschlossen, dass die Schichten auf den STO-Einkristallen Spannungsgradienten in den Schicht-normalen besitzen und an der Grenzfläche zum Substrat am stärksten verspannt sind. Die (111) orientierten Multilagen auf den STO-Einkristallen zeigen gegenüber den Schichten auf den (100) orientierten STO-Einkristallen eine deutlich erhöhte Interfacerauhigkeit. Vermutet wird, dass dies einerseits durch die andere kristallographische Orientierung der Wachstumsnormalen bedingt ist, weil damit jeweils keine geschlossenen SrO- bzw. BaO- und TiO3-Lagen ausgebildet werden. Andererseits zeigen die TEM-Aufnahmen eine deutliche Zunahme der Welligkeit der Einzellagen mit wachsendem Abstand vom Substrat, die rein mechanischen Effekten zugeschrieben wird. Die Verwölbung der Einzellagen könnte damit der Reduzierung der mechanischen Energie innerhalb des Systems dienen, wobei die Netzebenen dem Verlauf der Einzellagen folgen. Auf platinbeschichteten Siliziumsubstraten konnten erstmals phasenreine (111) fasertexturierte Mischschichten und BTO/STO-Multilagen abgeschieden werden. Grundlage hierfür war die Optimierung des Pt/Ti/SiO2/Si Schichtsystems hinsichtlich seiner thermischen Stabilität bis zu 800°C. Die Textur der Schichten wird von der Platingrundelektrode übernommen und deren Rauhigkeit teilweise verstärkt. Eine mechanische Verwölbung der Einzellagen konnte hier nicht beobachtet werden. Für die elektrischen Messungen wurden auf allen Schichten etwa 50 nm dicke Platinelektroden durch eine Hartmaske mittels Elektronenstrahlverdampfung im Hochvakuum bei etwa 300°C aufgebracht. Anschließend wurden die Schichten an Luft getempert, um das Sauerstoffdefizit, dass sich bei der Elektrodenabscheidung einstellt, auszugleichen. Die elektrischen Messungen zeichnen sich durch den sehr großen untersuchten Temperaturbereich aus. Temperaturabhängige Messungen im Bereich von 30-600 K finden sich für ferroelektrische Dünnschichten sehr selten in der Literatur und stellen für BTO/STO-Multilagen ein Novum dar. Auch die biasabhängige und teilweise auch temperaturabhängige Messung der Kapazität der Multilagen (C-V-Messungen) ist bisher einmalig. Durch die temperaturabhängigen Hysteresemessungen wurden Einblicke in den elektrischen Polungszustand der Schichten erhalten. Dadurch wird eine sinnvolle Interpretation der ε(T)-Kurven erst möglich. Der Vorteil der Integration des Polarisationsstromes unter Verwendung einer Dreieckspannung als Messsignal besteht in der direkten physikalischen Aussage der Strom-Spannungskurven über die Schaltspannung der Schichten
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Kolodiazhnyi, Taras Petric Anthony. "Semiconducting and dielectric properties of barium titanates, tantalates and niobates with perovskite structure /." *McMaster only, 2002.
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Mouron, Paule. "Cristallochimie de titanates de cuivre (+2) substitués appartenant aux types Corindon, Perovskite, Bixbyite et Braunite." Grenoble 2 : ANRT, 1988. http://catalogue.bnf.fr/ark:/12148/cb37616780f.
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Mouron-Metivier, Paule. "Cristallochimie de titanates de cuivre (+2) substitues appartenant aux types corindon, perovskite, bixbyite et braunite." Orléans, 1988. http://www.theses.fr/1988ORLE2033.
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Synthese et caracterisation de plusieurs series de titanates de cu#2#+ substitues cu#xti#xa#1##xb#1##xo#3 conduisent aux resultats suivants: maintien de la structure abo#3 de depart (ox0,25): corindon desordonne (a=b=fe) et ordonne type linbo#3 (a=li; b=nb, ta); apparition de structures nouvelles (x0,66): perovskite ordonnee (a=li; b=nb, ta), ou le lithium est a la fois en coordinence 4 carre a cote du cuivre et au sein des cavites icosaedriques; bixbyite desordonnee (a=b=fe) ou la specificite cristallochimique du couple (cu, ti) est demontree et cu#2#+#xti#2##xsb#xo#9 dont l'originalite structurale est l'existence d'un ordre sb#5#+/cu#2#+ sur les octaedres reguliers et deformes respectivement. (cu#2#+, ti#4#+) peut remplacer partiellement mn#3#+ dans la structure braunite apparentee au type bixbyite, en donnant des solutions solides de formulation generale mn#2#+mn#3#+#6##2#xcu#x#2#+ti#x#4#+sio#1#2
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Belkaoumi, Mohamed. "Spectroscopie d'impédance dans les perovskites oxidiques : applications à l'etude des relaxations dans BaTiO3 pur et dopé." Dijon, 1992. http://www.theses.fr/1992DIJOS013.
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Nous décrivons dans ce travail des mesures diélectriques réalisées par spectroscopie d'impédance dans un grand intervalle de températures (4k≤T≤1500K) et une large bande de fréquences (5Hz≤f≤1GHz) sur des monocristaux de BaTiO3 purs et dopés. Dans BaTiO3 dopé (Fe;Nb) une relaxation diélectrique à basse fréquence apparait et dépend de la concentration du dopant à toutes les températures. Dans BaTiO3 pur cette relaxation n'apparait dans notre gamme de fréquences qu'à des températures T>600K. Cette relaxation est décrite par la loi de Debye. Nous avons montré que la force de cette relaxation augmente avec la concentration en lacunes d'oxygène, qu'on peut faire varier par traitement à haute température dans une atmosphère réductrice ou oxydante. Nous attribuons ce mode de relaxation basse fréquence à la présence de charges d'espace dans l'échantillon. Cette charge d'espace est très sensible à la présence des lacunes d'oxygène, sources de charges libres et des niveaux d'impuretés. La seconde partie de ce travail traite les résultats de dispersion diélectrique dans BaTiO3:Nb en fonction de la fréquence (5Hz≤f≤1GHz) et la température (10 K≤t≤450K). La principale caractéristique de cette étude est le lien établi entre l'augmentation de la conductivité électronique de BaTiO3:Nb et la très grande amplitude de relaxation à f≈5. 10 6Hz pour toute température T>150K. Dans la phase rhomboédrique de BaTiO3:Nb (T<180K) un ralentissement important de la relaxation est observé, le temps de relaxation atteint 10-2s à 20K. Tandis que l'amplitude de la relaxation reste constante. L'effet précurseur de ce ralentissement est un maximum de la conductivité statique. Un modèle simple de couplage électron-relaxateur est proposé pour expliquer ce comportement.
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Abel, Stefan. "Dispositifs électro-optiques à base de titanate de baryum épitaxié sur silicium pour la photonique intégrée." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENT004/document.
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En premier lieu, des couches minces épitaxiales ont été obtenues sur des substrats de silicium grâce à l’utilisation de l’épitaxie par jets moléculaire et de couches tampons de titanate de strontium SrTiO3. Une technique de croissance par co-déposition a été développée de manière à obtenir un rapport Ba:Ti proche de la stoechiométrie, et ce afin d’éviter la formation de défauts cristallins dans la couche de BaTiO3. Le matériau déposé cristallise dans une structure de symétrie quadratique, ce qui est unpré-requis pour l’obtention de propriétés électro-optiques. De plus, selon les conditions de croissance, l’axe c de la maille élémentaire quadratique a pu être ajusté de manière à être aligné parallèlement ou perpendiculairement à la surface du substrat. L’utilisation d’une mince couche tampon de nucléation a également permis de croitre des films mincesBaTiO3 épitaxiées par pulvérisation, technique largement répandue en milieu industriel.Un coefficient de Pockels élevé a par la suite été obtenu sur de tellescouches épitaxiées. La valeur mesurée de 148pmV est clairement supérieure aux valeurs admises dans la littérature pour d’autres matériaux nonlinéairestels que le niobate de lithium, pour lequel un coefficient de31pmV est rapporté. La méthode de caractérisation électro-optique développée à cette occasion révèle également le caractère ferroélectrique des couches de BaTiO3, observé pour la première fois dans de tels matériaux épitaxiés sur silicium.Finalement, ces couches minces électro-optiquement actives ont été intégrées dans des dispositifs photoniques sur silicium. Dans cette optique,une structure de guide d’onde à fente a été utilisée en insérant 50nm deBaTiO3 entre deux couches de silicium. Dans ce type de structure, le confine mentoptique est 5 fois supérieur à celui obtenu pour des guides d’onde en silicium avec une gaine à base de BaTiO3. Des guides d’ondes rectilignesont tout d’abord été fabriqués, pour lesquels des pertes optiques del’ordre de 50−100 dB/cm ont été mesurées. Par la suite, des composants passifs fonctionnels ont été fabriqués, tels que des interféromètres typeMach-Zehnder, des résonateurs circulaires et des coupleurs. Finalement,la fonctionnalité de composants actifs a été démontrée pour la première fois, en se basant notamment sur des résonateurs ayant un facteur de qualité Q d’environ 5000, et pour lequel la résonance varie en fonction du champ électrique transverse. L’origine physique de cette variation n’a cependant pas pu être expliquée sur la seule base de l’effet Pockels. Cette thèse démontre que l’utilisation de nouveaux matériaux électro optiquement actifs au coeur de dispositifs photoniques sur silicium créede nouvelles opportunités pour la conception et l’ingénierie de circuitsphotoniques. L’intégration d’oxydes tels que barium titanate permet d’envisager de nouveaux concepts de dispositifs pour ajuster, moduler ou commuter la lumière au sein de circuits photoniques denses. De nouveaux défis et perspectives s’ouvrent également aux scientifiques pour modifier artificiellement les propriétés électro-optiques de ces matériaux, que ce soit par contrainte, dopage ou par l’ingénierie de multicouches. De telles avancées pourront sans aucun doute fortement améliorer les performances des dispositifsA novel concept of utilizing electro-optical active oxides in silicon photonic devices is developed and realized in the frame of this thesis. The integration of such oxides extends the silicon photonics platform by non-linear materials, which can be used for ultra-fast switching or low-power tuning applications. Barium titanate is used as active material as it shows one of the strongest Pockels coefficients among all oxides. Three major goals are achieved throughout this work: First, thin films of BaTiO3 are epitaxially grown on silicon substrates via molecular beam epitaxy (MBE) using thin SrTiO3 buffer layers. A shuttered co-deposition growth technique is developed in order to minimize the formation of defects in the BaTiO3 films by achieving a 1:1 stoichiometry between barium and titanium. The layers show a tetragonal symmetry and are therefore well-suited for electro-optical applications. The orientation of the long c -axis of the BaTiO3 crystal can be tuned to point perpendicular or parallel to the film surface, depending on the growth conditions. In addition, thin MBE-grown seed layers are combined with rf-sputter deposition. With this hybrid growth approach, rather thick ( > 100 nm), epitaxial BaTiO3 layers on silicon substrates are obtained with a commercially available, wide spread deposition technique. As a second goal, a strong Pockels coefficient of reff = 148 pm/V is determined in the epitaxial BaTiO3 films. This first experimental result on the electro-optical activity of BaTiO3 layers on silicon shows a clear enhancement compared to alternative non-linear materials such as lithium niobate with reff = 31 pm/V. By means of the electro-optical characterization method, also the presence of ferroelectricity in the films is demonstrated. Third, the electro-optical active BaTiO3 layers are embedded into silicon photonic devices. For this purpose, a horizontal slot-waveguide structure with a ~50 nm-thick BaTiO3 film sandwiched between two silicon layers is designed. With this design, the optical confinement in the active BaTiO3 layer is enhanced by a factor of 5 compared to Si-waveguide structures with a standard cross section and BaTiO3 as cladding. Straight BaTiO3 slot-waveguides with propagation losses of 50 − 100 dB/cm as well as functional passive devices such as Mach-Zehnder-interferometers, couplers, and ring resonators are experimentally realized. Additionally, first active ring resonators with Q-factors of Q~5000 are fabricated. The physical origin of the observed resonance shift as a function of the applied bias voltage, however, can not be conclusively clarified in the present work. The combination of high-quality, functional BaTiO3 layers with silicon photonic devices as demonstrated in this thesis offers new opportunities by extending the design palette for engineering photonic circuits with the class of electro-opticalactive materials. The integration of oxides such as BaTiO3 enables novel device concepts for tuning, switching, and modulating light in extremely dense photonic circuits. The integration also opens exciting challenges for material scientists to tailor the electro-optical properties of those oxides by strain engineering or fabrication of superlattice structures, which could ultimately lead to another boost of their electro-optical properties
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Hasegawa, Haroldo Lhou. "Crescimento de grãos anômalos em titanato de bário." Universidade Federal de São Carlos, 2004. https://repositorio.ufscar.br/handle/ufscar/763.
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Previous issue date: 2004-04-05Universidade Federal de Sao Carlos
Barium Titanate (BaTiO3) and derived material are extensively used in the manufacture for a large range of electronic components like multilayer ceramic capacitors (MLCC), semi-conductor devices, PTCR (positive temperature coefficient resistor) and electro-optic devices. Advanced ceramic powders preparation is playing an important role in modern ceramic research. Solid state synthesis of barium titanate has been studied in turning of the physical and chemical characteristics of the raw materials with special attention to the impurity levels, particle size distribution and particle morphology. Barium titanate has been in use for more than fifty years but important of the microstructure development is still needed for electronic ceramics in the future. The present work investigates the microstructural changes, mainly abnormal grain growth during the sintering of undoped and doped BaTiO3, with yttrium and barium. Samples doped with at least 0.15% mol of yttrium presented abnormal grain in a size around 50 µm and samples doped with at least 0.15% mol of barium presented abnormal grain in a size around 25 µm. Such fact can be attributed to the presence of localized liquid phase, during the sintering, leading to formed dissolution (or precipitation) sites and resulting in abnormal grain growth.
O titanto de bário e seus derivados têm sido extensamente utilizados para fabricação de vários tipos de componentes eletrônicos como, por exemplo, capacitores cerâmicos em multicamadas (MLCC), termistores (PTC) e componentes eletros-óticos entre outros. A preparação de pós cerâmicos tem se tornado parte importante na fabricação de materiais cerâmicos modernos. A síntese via estado sólido do titanato de bário continua sendo estudado em função de suas características físicas e químicas e especialmente em termos de pureza, distribuição de partículas e morfologia das partículas.O titanato de bário tem sido utilizado por mais de cinqüenta anos, porém o desenvolvimento microestrutural continua sendo o foco principal para o desenvolvimento de futuros componentes eletrônicos. O presente projeto de pesquisa objetivou comparar e analisar o desenvolvimento da microestrutura durante o processo de sinterização, principalmente em relação a aparição de grãos exageradamente crescidos em cerâmicas baseadas em BaTiO3 sem dopagem e dopadas com ítrio e bário. As amostras dopadas com teores superiores a 0,15% em mol de bário apresentaram grãos na ordem de 25µm e as amostras com teores de ítrio superiores a 0,15% em mol apresentaram grãos da ordem de 50µm.Tal fato pode estar relacionado com a presença de fases líquidas localizadas originando pontos de precipitação resultando em grãos anômalos.
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Shafi, Shahid. "Solid State Structure-Reactivity Studies on Bixbyites, Fluorites and Perovskites Belonging to the Vanadate, Titanate and Cerate Families." Elsevier, 2012. http://hdl.handle.net/1993/8909.
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This thesis primarily focuses on the systematic understanding of structure – reactivity relationships in two representative systems: bixbyite and related structures as well as indium doped CeO2. Topotactic reaction routes have gained significant attention over the past two decades due to their potential to access kinetically controlled metastable materials. This has contributed substantially to the understanding of solid state reaction pathways and provided first insights into mechanisms. Contrary to the widely used ex-situ methods, in – situ techniques including powder x-ray diffraction and thermogravimetric – differential thermal analysis have been employed extensively throughout this work in order to follow the reaction pathways in real time.
Detailed analysis of the AVO3 (A = In, Sc) bixbyite reactivity under oxidative conditions has been carried out and a variety of novel metastable oxygen defect phases have been identified and characterized. The novel metastable materials have oxygen deficient fluorite structures and consequently are potential ion conductors. Structural aspects of the topotactic vs. reconstructive transformations are illustrated with this model system. The structure – reactivity study of AVO3 phases was extended to AVO3 perovskite family.
Based on the research methodologies and results from AVO3 bixbyite reactivity studies a generalized mechanistic oxidation pathway has been established with a non-vanadium phase, ScTiO3 bixbyite. However, there is stark contrast in terms of structural stability and features beyond this stability limit during AVO3 and ScTiO3 bixbyite reaction pathways. A series of complex reaction sequences including phase separation and phase transitions were identified during the investigation of ScTiO3 reactivity.
The two-step formation pathway for the fluorite – type oxide ion conductor Ce1-xInxO2-δ (0 ≤ x ≤ 0.3) is being reported. The formation of the BaCe1-xInxO3-δ perovskites and the subsequent CO2-capture reaction with the formation of Ce1-xInxO2-δ (0 ≤ x ≤ 0.3) has been investigated in detail. The two-step formation pathway is contrasted with the unsuccessful direct method. The stability and the extent of In – doping for the CeO2 fluorite phases that can be achieved through this CO2 – capture method are reported. The necessity and strategies for the selection of appropriate intermediate precursors for the preparation of doped CeO2 are also reported.
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Bacha, Elsy. "Développement par voie chimique à basse température de couches minces perovskite de titanates de baryum et de strontium." Nantes, 2010. http://archive.bu.univ-nantes.fr/pollux/show.action?id=a54e2d4c-9054-4414-a467-d4e9a15a7672.
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La permittivité élevée des ferroélectriques permet leur utilisation dans des composants électroniques. Elle dépend des propriétés intrinsèques, de la compacité du dépôt en couche mince, de sa rugosité, des défauts tels que lacunes d'oxygène en cas d'élaboration à température élevée. . . L'objectif de ces travaux vise à développer des films ferroélectriques compacts et denses à basse température. Deux procédés de synthèse ont été examinés. Le premier est basé sur un dépôt par électrophorèse à température ambiante de nanocristaux de BatiO3 et SrTiO3, synthétisés par voie solvothermale en milieu aqueux à partir de précurseurs inorganiques, puis stabilisés dans des solutions colloïdales. Les structures, compositions chimiques et morpholgies des nanocristaux sont étudiées par DRX, MET, MEB, spectroscopies FTIR et Raman, ATG / SM, densité, BET en fonction de la nature de la concentration des précurseurs et du traitement thermique. La spectroscopie de corrélation de photons et zétamétrie renseignent sur les tailles des nanocristaux et le domaine de stabilité des solutions colloïdales. Le deuxième procédé porte sur la synthèse directe, in-situ, sur substrat de titane par voie solvothermale. Il a permis l'obtention à T<200°C de couches denses et uniformes de BTO et STO présentant une légère orientation préférentielle. L'étude des propriétés diélectriques révèle l'existence de la phase quadratique de BaTiO3 mais aussi des pertes élevées à basses fréquences, attribuées aux charges d'espace inter-grains, qui se manifestent par un courant de diffusion. Les procédés développés ouvrent de nouvelles perspectives qui pourraient être étendues à d'autres oxydes de métaux de transitionThe high-k character of ferroelectric materials allows their utilisation in electronic devices. The permittivity depends on intrinsic properties, film compactness, surface roughness, defects like oxygen vacancies in the case of a high temperature crystallization, etc. The present work aims to the development of dense and compact ferroelectric films at low temperatures. Two synthesis routes have been studied. The first is room temperature electrophoretic deposition of BaTiO3 and SrTiO3 nanoparticles, which were elaborated from inorganic precursors in an aqueous solution by a solvothermal route and stabilized in colloidal suspensions. X-Ray diffraction, SEM, TEM, IR and Raman spectroscopy, TGA / MS, density, and BET were employed in order to study composition and morphology of the nanoparticles as a function of the precursor nature and concentration and the thermal treatment. Photon correlation spectroscopy and zeta potential measurements allow determination of the nanoparticles sizes and the conditions for a stable colloidal solution. The second route is a low temperature solvothermal in-situ synthesis, directly from a titanium substrate. Dense and uniform BTO and STO films, slightly textured in the (001) direction, are obtained at temperatures below 200°C. The study of the dielectric properties indicates the existence of the BaTiO3 tetragonal phase. Dielectric losses may be related to space charges located at the grain boundaries which give rise to diffusion currents at low frequencies. The synthesis route developed may open the way for new applications and may also be adapted to other transition metal oxides
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Paul, Michael. "Investigation of the defect structure and energetics of nickel doped alkaline earth perovskite-type titanates using computational chemistry modelling." Thesis, University College London (University of London), 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.497808.
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Wang, Pengjiu. "Conception de contacts oxydes et de pérovskites à cations mixtes pour des cellules solaires hautement efficaces." Thesis, Paris Sciences et Lettres (ComUE), 2018. http://www.theses.fr/2018PSLEC019.
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Base perovskite-cellules solaires (CSP) ont émergé comme la nouvelle génération la plus prometteuse du photovoltaïque technology.Organometal trihalogénure perovskite cellules solaires (PSC) ont suscité intérêts académiques et commerciaux répandus en raison de rapide accroître l'efficacité, qui a stimulé de 3,8% 4 en 2009 à 20,1% 5 en 2014. Ces grandes réalisations sont principalement attribué aux caractéristiques particulières des matériaux pérovskites, comme le faible coût, haute photo à électrique rendement de conversion, propriétés d'absorption de lumière élevés, bandgap directe, haute charge- la mobilité des porteurs et électron-trou à long transport exciton la distance (plus de 1 um). 6-8 matériau perovskite est soluble, ce qui le rend très facile et pas cher pour préparer solaire perovskite cellulesPerovskite-based solar cells (PSCs) have emerged as the most promising new generation of photovoltaic technology.Organometal trihalide perovskite solar cells (PSC) have aroused widespread academic and commercial interests due to rapid increase in efficiency, which has boosted from 3.8%4 in 2009 to 20.1%5 in 2014. These great achievements are mainly attributed to the unique characteristics of perovskite materials, such as low cost, high photo-to-electric conversion efficiency, high light absorption properties, direct bandgap, high charge- carrier mobility and long electron-hole exciton transport distance (more than 1 µm). 6-8 Perovskite material is soluble, which makes it quite easy and cheap to prepare perovskite solar cells
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Neagu, Dragos. "Materials and microstructures for high temperature electrochemical devices through control of perovskite defect chemistry." Thesis, University of St Andrews, 2013. http://hdl.handle.net/10023/3606.
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The development of technologies that enable efficient and reliable energy inter-conversion and storage is of key importance for tempering the intermittent availability of renewable energy sources, and thus for developing an energy economy based on sustainable, clean energy production. Solid oxide electrolysis cells (SOECs) may be used to store excess electrical energy as hydrogen, while solid oxide fuel cells (SOFCs) could convert back hydrogen into electricity, thus balancing energy availability and demand. However, the current state-of-the-art hydrogen electrode used in both SOECs and SOFCs, the Ni-yttria-stabilised zirconia cermet (Ni-YSZ), is unreliable in conjunction with intermittent energy sources, in particular due to its innate redox instability. This thesis explores the fundamental properties of various inherently redox stable A-site deficient titanate perovskite systems (A1-αBO3, B = Ti), seeking to uncover the principles that enhance their properties so that they may be used to replace Ni-YSZ. In particular, this work demonstrates that the versatility of perovskites with respect to the introduction of lattice defects such as vacancies and cation substitutions enables considerable improvements in the extent of reduction, electronic conductivity and overall electrochemical activity. Most importantly, the defect chemistry context set by the presence of A-site vacancies was found to trigger the exsolution of electrocatalytically active nanoparticles from the parent perovskite, upon reduction. This is an entirely new phenomenon which was explored and exploited throughout this study to produce perovskite surfaces decorated with uniformly distributed catalytically active nanoparticles. As demonstrated in this study, the exsolution phenomenon excels in terms of producing nanoparticles with uniform size, distribution, diverse composition and ‘unconventional' surface anchorage. The resulting enhanced properties, and especially the exsolution phenomenon, contributed coherently towards improving the suitability of the perovskites developed here towards their application as hydrogen electrode materials. Consequently, when integrated into SOEC button cells as hydrogen electrodes, they exhibited a step-change increase in performance compared to other perovskites considered to date. Many of the principles and perovskite defect chemistry explored and exemplified in this study on perovskite titanates may be extended to other perovskites as well. In particular the advanced control and understanding achieved in this work over the exsolution phenomenon may inspire the formulation of new and sophisticated oxide materials with advanced functionality.
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Engelmayer, Johannes [Verfasser], Thomas [Gutachter] Lorenz, and Markus [Gutachter] Braden. "Crystal growth and characterization of doped perovskite titanates ATiO3 and single-layered manganites R1-xA1+xMnO4 / Johannes Engelmayer ; Gutachter: Thomas Lorenz, Markus Braden." Köln : Universitäts- und Stadtbibliothek Köln, 2020. http://d-nb.info/1225478472/34.
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Roudeau, Sabine. "Nouveaux matériaux d'anodes pour pile à combustible SOFC fonctionnant à 700 °C." Bordeaux 1, 2008. http://www.theses.fr/2008BOR13588.
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FUJIMOTO, TALITA G. "Microestrutura e propriedades elétricas e dielétricas do titanato de estrôncio puro e contendo aditivos." reponame:Repositório Institucional do IPEN, 2016. http://repositorio.ipen.br:8080/xmlui/handle/123456789/26933.
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O titanato de estrôncio (SrTiO3) possui estrutura cristalina do tipo perovsquita. Materiais com este tipo de estrutura são utilizados para diversas aplicações, tais como, sensores, atuadores, em células a combustível de óxido sólido, entre outros. Devido as suas interessantes propriedades físicas, o SrTiO3 vem sendo intensamente estudado, em especial com a introdução de dopantes. Portanto, neste trabalho foi investigada a influência de diferentes teores de Ca (1; 2,5 e 5% mol) e Pr (0,025; 0,050; 0,075 e 1% mol) na microestrutura e propriedades elétricas e dielétricas do SrTiO3, assim como o material sem aditivos (puro). Os resultados mostram que após a sinterização do SrTiO3 puro, a microestrutura consiste de grãos poligonais com tamanho médio micrométrico, além de texturas lisas e rugosas. A condutividade elétrica das amostras sintetizadas sinterizadas a 1450 e 1500ºC é máxima para 2 horas de patamar. Apenas as amostras de SrTiO3 contendo 1% em mol de Ca apresentam fase única. O tamanho médio de grãos das amostras contendo 1% em mol de Ca é 10,65 ± 0,28 µm e para teores acima deste valor ocorre crescimento significativo dos grãos. As medidas de condutividade elétrica mostraram que as amostras contendo a adição de 1% em mol de Ca possuem maior condutividade dos grãos em relação ao material puro. Para as amostras contendo teores de até 0,075% mol de Pr, pode-se observar alguns grãos lisos e outros rugosos e não há variação considerável do tamanho médio de grãos. As amostras contendo menor teor de Pr (0,025% mol) apresentam maior condutividade dos grãos e contornos de grãos. As amostras de SrTiO3 sintetizado sinterizadas a 1450ºC/10 h apresentaram permissividade elétrica colossal em temperatura ambiente em altas frequências.
Dissertação (Mestrado em Tecnologia Nuclear)
IPEN/D
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP
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Kazaoui, Saïd. "Etude diélectrique en hyperfréquences de céramiques ferroélectriques de compositions dérivées de BaTiO3." Phd thesis, Université Sciences et Technologies - Bordeaux I, 1991. http://tel.archives-ouvertes.fr/tel-00835501.
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Une étude systématique du phénomène de relaxation diélectrique dans les gammes de fréquence 1 MHZ-1GHZ et de température de 250-500 K, a été effectuée sur des céramiques de titanate de baryum substituées. Il existe, quelle que soit la composition, un minimum de la fréquence de relaxation et un maximum de la dispersion diélectrique à chaque température de transition de phases. La relaxation est de type dipolaire ; elle est liée au déplacement des ions, en site octaédrique disposés suivant des chaînes (ou volume) de corrélation.
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Joo, Gi-Tae. "Nouvelles phases ferroélectriques non stoechiométriques de type perovskite ou LiTaO3." Phd thesis, Université Sciences et Technologies - Bordeaux I, 1986. http://tel.archives-ouvertes.fr/tel-00203505.
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Etude de la constante diélectrique, spectres Mössbauer et RMN. Les transitions de phases sont étudiées par diffraction RX et mesures diélectriques. Les systèmes étudiés sont : PbTiO3-1/2Pb2Fe2O5-CaTiO3-1/2Ca2fE2O5; Li2O-Ta2O5-MgO; Li2O-Ta2O5-ZnO; Li2O-Ta2O5-MgO.
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PORFIRIO, TATIANE C. "Preparação e caracterização microestrutural e dielétrica da perovsquita CaCusub(3)Tisub(4)Osub(12)." reponame:Repositório Institucional do IPEN, 2015. http://repositorio.ipen.br:8080/xmlui/handle/123456789/24066.
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Tese (Doutorado em Tecnologia Nuclear)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Rigoni, João Francisco. "“Síntese e caracterização de perovskitas sem e com dopagem de Nb2O5”." UNIVERSIDADE ESTADUAL DE PONTA GROSSA, 2014. http://tede2.uepg.br/jspui/handle/prefix/2134.
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Previous issue date: 2014-08-08Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
The current technological development in the communication, has carrieb, data processing, integration of devices and entertainment, is only possible due to the advances integrated and continuos of the research on new materials to be applied in the technological industry,lighter, cheaper with better incomes. In the work it was become fulfilled synthesis and of the Titanate od calcium and has covered – pure CCTO and its doped version with different ratios of Nb+5 , by means of the method of reaction for solid state. This materials has shown interesting and pertinent physical properties to the current industry technological, as material mainly dielectric. The characterization of material obtained was made through the techniques of diffraction of X-rays (XRD), structural analysis for the Method of Rietveld, morphological and compositional characterization using scanning electron microscopy (SEM), dispersive spectroscopy X-ray (EDX), in addition to the characterization by Raman spectroscopy, and determination of the “band gap” by diffuse reflectance. The gotten, pure and doped samples had been identified as being the material of interest, proven through the described instrumental techniques previously. The gotten Values of “band gap” better present small variation, being able to be studied with use of others techniques.
O desenvolvimento tecnológico atual, na comunicação, transporte, processamento de dados, integração de aparelhos e entretenimento, só é possível graças aos avanços integrados e contínuos das pesquisas sobre novos materiais a serem aplicados na indústria tecnológica, mais leves mais baratos com melhores rendimentos. Neste trabalho realizou-se a síntese e do Titanato de cálcio e cobre – CCTO puro e sua versão dopada com diferentes proporções de Nb+5 , Poe meio do método de reação por estado sólido (RES). Esse material tem exibido propriedades físicas interessantes e pertinentes à indústria tecnológica atual, principalmente como material dielétrico. A caracterização do material obtido foi realizada através das técnicas de difração de raios X (DRX), análise estrutural pelo Método Rietveld, caracterização morfológica e composicional usando microscopia de varredura eletrônica (MEV) e espectroscopia dispersiva de raios X (EDS), bem como a caracterização por espectroscopia de RAMAN e determinação de “banb gap” por reflectância difusa. As amostras obtidas, puras e dopadas foram identificadas como sendo o material de interesse, comprovado através das técnicas instrumentais descritas anteriormente. Os Valores de “band gap” obtidos apresentam pequena variação, podendo ser melhor estudadas com uso de outras técnicas.
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Lamarti-Sefian, Samir. "Elaboration et caractérisation de couches minces supraconductrices à haute température critique : études de nouvelles perovskites oxygénées comportant du cuivre et du titane." Bordeaux 1, 1991. http://www.theses.fr/1991BOR10591.
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Lamarti, Sefian Samir. "1er sujet : Elaboration et caractérisation de couches minces supraconductrices a haute température critique. 2ème sujet : Etude de nouvelles perovskites oxygénées comportant du cuivre et du titane." Phd thesis, Université Sciences et Technologies - Bordeaux I, 1991. http://tel.archives-ouvertes.fr/tel-00165234.
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La première partie de cette thèse décrit l'élaboration et la caractérisation de couches minces supraconductrices de composition YBa2Cu3O7-d. Leurs propriétés de transport ont été analysées dans le cadre de la théorie B.C.S. La deuxième partie est relative à la mise en évidence et à l'étude des propriétés structurales de nouvelles perovskites de composition Ln2CuTiO6-d (Ln=terre rare) et AxLn2-xCu1+yTi1-yO6-d (A=alcalinoterreux). Un modèle de distribution cationique reposant sur des études de diffraction X et de microscopie électronique est proposé.
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Fompeyrine, Jean. "Propriétés structurales et magnétiques de quelques phases dérivées de la perovskite dans les systèmes La-Ti-O et Ba-(M,M') - F-Cl (M,M' élément 3D)." Bordeaux 1, 1995. http://www.theses.fr/1995BOR10625.
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L'investigation du système La4TI3O12-LaTiO3 a permis de mettre en évidence une nouvelle série homologue de formulation LanTin-xO3n. Les structures de ces phases ont été caractérisées par diffraction des rayons X sur poudre et par microscopie électronique en transmission. Elles dérivent de différents polytypes de perovskites hexagonales et présentent une distorsion structurale due a la rotation coopérative des octaèdres autour de leurs axes ternaires. Une nouvelle serie de composes Ba2MM' F7Cl (M, M' = Mn, Fe, Co, Ni, Zn), dont les structures ont été déterminées par diffraction des rayons X sur monocristal, a été par ailleurs mis en évidence. Une étude comparative des propriétés structurales et magnétiques avec celles des composés de la série BaMF4 a été effectuée (filiation structurale résultant de différentes rotations coopératives des octaèdres, mesures d' aimantation sur poudre et monocristal, détermination des structures magnétiques de Ba2Co2F7Cl et Ba2Ni2F7Cl par diffraction des neutrons). Un nouveau chlorofluorure du cuivre a également été caractérise sur le plan structural et magnétique. Dans ce cas, une filiation structurale avec la structure de l'apatite et avec celle de phases derivees est proposée.
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Richter, Carsten. "Applications of resonant hard x-ray diffraction for characterization of structural modifications in crystals." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2018. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-229348.
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Die Arbeit behandelt die vielseitigen Möglichkeiten im Bereich der Kristallstrukturanalyse mit Röntgenstrahlung, welche sich zusätzlich bei resonanter Anregung von Elektronenübergängen ergeben. Existierende resonante Methoden aus diesem Bereich werden im materialwissenschaftlichen Kontext neu dargelegt und ausgebaut. Zudem werden neue Methoden zur Strukturverfeinerung vorgestellt, welche darauf zielen, mithilfe resonanter Anregung kleine Abweichungen von der Idealstruktur oder aber Phasenumwandlungen zu beschreiben. Im Vordergrund steht dabei die hier erstmals ausgearbeitete Methode der Unterdrückung von Beugungsintensität durch Variation der atomaren Streufaktoren über gezieltes Einstellen der Röntgenenergie. Dies ist stark abhängig von internen Strukturparametern und ermöglichte so eine pikometergenaue Bestimmung von Atompositionen in einer neuen, polaren Oberflächenschicht des Strontiumtitanats. Weitere Anwendungen auf verschiedene Klassen kristalliner Materialien werden vorgestellt und basieren auf unterschiedlichen Aspekten resonanter Beugung wie zum Beispiel verbotenen Reflexen.
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Souza, James Alves de. "Simulações por dinâmica molecular de compostos do tipo ABO3 (SrTiO3 e CaTiO3)." Universidade Federal de São Carlos, 2009. https://repositorio.ufscar.br/handle/ufscar/5016.
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Previous issue date: 2009-02-26Universidade Federal de Minas Gerais
Using the classical molecular dynamics simulations, Perovskites systems composed by oxides (ABO3), in particular SrTiO3 and CaTiO3, were performed. The titanates are easily prepared as polycrystalline ceramics; chemically and mechanically stable they can be characterized in various temperature and pressure conditions. These provide us reliable experimental results for construction and consolidation of theoretical models. Another important fact is that these materials have wide variety of technological applications and many important properties as well as the phase transitions arising from the effect of temperature and pressure. That can be explored to understand the interactions among its constituents. The effective interatomic potential used has the same functional form of the potential proposed by Vashishta and Rahman and it s composed by the sum of terms Coulomb interaction, van der Waals, esthereometric and dipole-induced. The system was treated in (N, V, E) and (N, P, H) ensembles to verify the influence of temperature and pressure application on structural and dynamics properties of perovskites. The method used allowed us to describe various properties such as thermal expansion coefficient, angles distribution, coordination number, elastic properties, pair distribution function, density of vibrational states, Debye-Waller factor and so on. The phase transitions of systems were explored showing fantastic results.
Utilizando o método da Dinâmica Molecular clássica foram realizadas simulações de sistemas perovskitas formados por óxidos (ABO3), em particular SrTiO3 e CaTiO3. A vantagem em trabalhar com estes materiais é que os titanatos são facilmente preparados como cerâmicas policristalinas, são química e mecanicamente muito estáveis, o que torna possível caracterizálos em várias condições de temperatura e pressão, nos proporcionando resultados experimentais confiáveis para construção e consolidação de modelos teóricos. Outro fato importante é que estes materiais possuem ampla aplicabilidade tecnológica além de propriedades como transições de fase decorrentes do efeito de temperatura e pressão que podem ser exploradas para o melhor entendimento das interações entre seus constituintes. O potencial interatômico efetivo utilizado possui a mesma forma funcional dos potenciais propostos por Vashishta e Rahmann sendo composto pela soma dos termos de interação de Coulomb, de van der Waals, estereométrica e carga-dipolo induzido. Os sistemas foram tratados nos ensembles microcanônico (N,V,E) e isobárico-isoentálpico (N,P,H) para verificação da influência da temperatura e aplicação de pressão em suas propriedades estruturais e dinâmicas. O método empregado nos permitiu descrever de maneira satisfatória várias propriedades como coeficiente de expansão térmica, distribuição de ângulos, número de coordenação, propriedades elásticas, função distribuição de pares, densidade de modos vibracionais, fator de Debye-Waller entre outros. O comportamento dos sistemas na região em que ocorrem as transições de fase também foi explorado apresentando resultados fantásticos.
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Fompeyrine, Jean. "Propriétés structurales et magnétiques de quelques phases dérivées de la perovskite dans les systèmes La-Ti-O et Ba(M,M') - F-Cl (M,M'élément 3 D)." Phd thesis, Université Sciences et Technologies - Bordeaux I, 1995. http://tel.archives-ouvertes.fr/tel-00148927.
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L'investigation du système La4TI3O12-LaTiO3 a permis de mettre en évidence une nouvelle série homologue de formulation LanTin-xO3n. Les structures de ces phases ont été caractérisées par diffraction des rayons X sur poudre et par microscopie électronique en transmission. Elles dérivent de différents polytypes de perovskites hexagonales et présentent une distorsion structurale due a la rotation coopérative des octaèdres autour de leurs axes ternaires. Une nouvelle serie de composes Ba2MM' F7Cl (M, M' = Mn, Fe, Co, Ni, Zn), dont les structures ont été déterminées par diffraction des rayons X sur monocristal, a été par ailleurs mis en évidence. Une étude comparative des propriétés structurales et magnétiques avec celles des composés de la série BaMF4 a été effectuée (filiation structurale résultant de différentes rotations coopératives des octaèdres, mesures d' aimantation sur poudre et monocristal, détermination des structures magnétiques de Ba2Co2F7Cl et Ba2Ni2F7Cl par diffraction des neutrons). Un nouveau chlorofluorure du cuivre a également été caractérise sur le plan structural et magnétique. Dans ce cas, une filiation structurale avec la structure de l'apatite et avec celle de phases derivees est proposée.
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Perraudeau, Amélie. "Couches mésoporeuses de TiO2 déposés par PECVD à la pression atmosphérique en vue d'applications photovoltaïques." Thesis, Limoges, 2019. http://www.theses.fr/2019LIMO0092.
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Un système de dépôt chimique en phase vapeur assisté par plasma doté d’une torche à injection axiale (TIA) a été choisi pour l’élaboration des films de TiO2. Un mode de dépôt dynamique, i.e. en déplaçant le substrat face au plasma, a été mis en place dans l’objectif de recouvrir des surface de l’ordre du centimètre carré. En vue d’utiliser les films de TiO2 en tant que couche active au sein de DSSCs, une structure mésoporeuse colonnaire et cristallisée sous forme anatase doit être idéalement obtenue. L’analyse du plasma, sans et avec le précurseur du titane, par spectroscopie d’émission optique a permis de mettre en évidence les flux de chaleur importants pouvant être transférés au substrat par le jet de plasma, avec des températures de gaz comprises entre 3000 et 4000 K, de 5 à 15 mm au-dessus de la buse. L’évaluation des densités relatives d’espèces atomiques et notamment de l’azote, de l’oxygène et du titane, combinée à l’étude de l’influence des conditions opératoires sur la microstructure du film a permis de mettre en évidence différents mode de croissance des couches de TiO2. Grâce à ces observations, un diagramme de microstructure de la couche de TiO2 déposée sur un substrat en silicium a été construit pour prédire plus facilement la morphologie et le caractère cristallin des films en fonction de la puissance microonde et de la distance torche-substrat. Dans certaines conditions, il est possible d’obtenir une structure correspondant au cahier des charges de la couche active des DSSCs. Le transfert de cette microstructure sur des substrats verre/FTO, faits pour l’application photovoltaïque, a nécessité une adaptation de la puissance micro-onde et de la distance torche-substrat de travail. La microstructure obtenue a permis de valider le diagramme de microstructure établi dans ces travaux, malgré l’obtention d’une couche ne correspondant pas au cahier des charges. Finalement, la fabrication de cellules solaires pérovskite a été initiée en exploitant le dépôt de TiO2 réalisé sur substrat en siliciumAn atmospheric pressure chemical vapor deposition process equipped with an axial injection torch was chosen for the TiO2 thin films synthesis. A dynamic deposition mode, i.e. moving the substrate holder in front of the plasma jet, was developed to cover a square centimeter surface. Towards the integration of the titania films as the active layer in DSSCs, a porous columnar structure crystallized under the anatase phase was required. The optical emission spectroscopy analysis of the discharge, without and with titanium precursor, provided information about the huge thermal flux transferred to the substrate by the plasma, thanks to gas temperature from 3000 to 4000 K, at distances between 5 and 15 mm from the nozzle. The atomic relative densities estimation, mainly of nitrogen, oxygen and titanium, combined with the process parameters influence on the film microstructure highlighted several growth mechanisms. From these results, a microstructure diagram was built to predict more easily the morphology and the crystallinity of the TiO2 films deposited on silicon substrates, as a function of microwave power and torch-substrate distance. Optimized conditions were found for the synthesis of thin films matching the DSSC active layer specifications. The process parameters were then adapted to replicate the microstructure on glass/FTO substrates, confirming the microstructure diagram, even though the thin film did not fulfill the requirements. Perovskite solar cells were finally made to investigate the interest of the layers developed on silicon substrates
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Lin, Yi-Ru, and 林憶如. "Hydrothermal Synthesis of Barium Titanate and Complex Perovskite Nanopowder." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/99563543198095684763.
Full textAbstract:
碩士義守大學
材料科學與工程學系
92
The synthesis of nano-size Barium Titanate (BaTiO3) and (Ba1-xCax)(Ti1-yZry)O3 perovskite solid solution powders where x = y = 0.05~0.20 have been investigated by using hydrothermal method in strong alkaline solution at the temperature range of 130~280℃ using chlorides as starting materials soursces.The crystallized powders were characterized by powder x-ray diffraction (XRD) decides its crystallization structure, by the Field Emission Scanning electron microscopy (FE-SEM), the Transmission electron microscopy (TEM) decides its particles size and the shape, estimates its particle size use Inductively coupled plasma mass spectrometer (ICP-MS) and the Energy dispersive spectrometer (EDS) carries on element of the powder qualitative respectively. The results indicated that both BaTiO3 and (Ba1-xCax)(Ti1-yZry)O3 perovskite solid solution powders were crystalline phases with particle size of 30~100nm. The experimental result showed that, enhances [Ba]/[Ti] ratio, its particle size is decrease with the Ba/Ti ratio increase; Increase the excess of the sodium hydroxide and the tetrachloride titanium initiate concentration all can cause the barium titanate particle size to decrease; Powder morphology and particle size and reaction temperature related, when low reaction temperature for the finely ground particles aggregation, the high reaction temperature is helpful disperser of to the particle, but also has the particle size uneven. But reaction time to its particles size and shape certainly not tremendous influence. The calcium and zirconium ion was add to the barium titanate, decides by the XRD analysis and has without the discovery is at variance with the barium titanate diffraction peak, demonstrated other like ZrO2, CaCO3 or CaZrO3 and so on is mixed, synthesis powder analysis by ICP and EDS, the definite calcium, zirconium truly has increases into in the barium titanate, therefore, deduces it truly to form the (Ba1-xCax) (Ti1-yZry)O3 solid solution.
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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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Lin, Yu-Wei, and 林育葳. "The Study of Perovskite Solar Cells by Using Calcium Titanate as Electrical Transfer Layer." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/00686385885426783897.
Full textAbstract:
碩士國立中央大學
機械工程學系
104
This study applies CaTiO3 as a mesoporous layer for Perovskite Solar Cells. We fabricated standard Perovskite Solar Cells as structure FTO/TiO2 compact layer/TiO2 mesoporous layer/ CH3NH3PbI3 active layer/Spiro-OMeTAD hole transfer layer/silver in both anode and cathode. This cell has Jsc=18.3mA/cm2, Voc=0.97V, FF=0.68 and PCE=12.1%。 Calcium is the 5th most abundant element in the world. We used calcium carbonate react with titanium dioxide and synthesized nano- CaTiO3/TiO2 powder as electrical transfer layer to enhance the crystallization of active layer (CH3NH3PbI3) and the turn-on voltage. Moreover, using nano-CaTiO3/TiO2 powder as a mesoporous layer of Perovskite Solar Cells and it performs Jsc=13.7mA/cm2, Voc=0.99V, FF=0.62 and PCE=8.4%. To extract the short-circuit current, we improve the coverage of mesoporous layer on FTO surface via two step spin-coating method. The mesoporous layer could avoid the active layer directly contacting FTO glass, which would result in short-circuit condition. In addition, the mobility of electrons would be enhanced due to the significant coverage of mesoporous layer. Which also increase the contact area between active layer and mesoporous layer. Consequently, increased contact area enhances the short-circuit current(Jsc) from 13.7 mA/cm2 to 16.2 mA/cm2 and also improves power conversion efficiency from 8.4% to 10.2%.
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"Transport properties of heterostructure p-n junction formed between perovskite manganites and niobium doped strontium titanate." 2005. http://library.cuhk.edu.hk/record=b5892675.
Full textAbstract:
Lai Chun Hei Gary = 錳氧化物-鈮摻雜之鈦酸鍶異構結的輸運特性 / 黎鎮禧.Thesis (M.Phil.)--Chinese University of Hong Kong, 2005.
Includes bibliographical references.
Text in English; abstracts in English and Chinese.
Lai Chun Hei Gary = Meng yang hua wu-ni shan za zhi tai suan si yi gou jie de shu yun te xing / Li Zhenxi.
Acknowledgement --- p.i
Abstract --- p.ii
論文摘要 --- p.iv
Table of contents --- p.vi
List of Figures --- p.x
List of Tables --- p.xv
Chapter Chapter 1 --- Introduction
Chapter 1.1 --- Introduction to perovskite manganites and niobium doped strontium titanate --- p.1-1
Chapter 1.1.1 --- Structure and properties of perovskite manganites --- p.1-1
Chapter 1.1.2 --- Structure and properties of niobium doped strontium titanate --- p.1-4
Chapter 1.1.3 --- Phase transition in perovskite manganites --- p.1-9
Chapter 1.1.4 --- Charge ordering and small polaron theory in PCMO --- p.1-15
Chapter 1.1.5 --- Colossal Magnetoresistance (CMR) in perovskite manganites --- p.1-19
Chapter 1.16 --- Review of semiconducting junction between perovskite manganites and niobium doped strontium titanate --- p.1-23
Chapter 1.2 --- Research motivation --- p.1-28
Chapter 1.3 --- Scope of this thesis --- p.1-29
References --- p.1-31
Chapter Chapter 2 --- Experimental details
Chapter 2.1 --- Thin film deposition --- p.2-1
Chapter 2.1.1 --- Facing-target sputtering --- p.2-1
Chapter 2.1.2 --- Vacuum system --- p.2-3
Chapter 2.1.3 --- Fabrication and characterization of manganites targets --- p.2-4
Chapter 2.1.4 --- Substrate --- p.2-7
Chapter 2.1.5 --- Deposition procedure --- p.2-8
Chapter 2.1.6 --- Silver electrode coating apparatus --- p.2-10
Chapter 2.2 --- Annealing systems --- p.2-12
Chapter 2.2.1 --- Vacuum annealing system --- p.2-12
Chapter 2.2.2 --- Oxygen annealing system --- p.2-14
Chapter 2.3 --- Characterization --- p.2-16
Chapter 2.3.1 --- Profilometer --- p.2-16
Chapter 2.3.2 --- X-ray diffractometer --- p.2-16
Chapter 2.3.3 --- Resistance measurement system --- p.2-18
Chapter 2.3.4 --- Current-voltage characteristics measurement system --- p.2-20
References --- p.2-23
Chapter Chapter 3 --- Epitaxial LCMO/STON heterojunction
Chapter 3.1 --- Four point and two point I-V measurement --- p.3-1
Chapter 3.2 --- Magnetic phase transition of LCMO revealed by four point I-V measurement of LCMO/STON heteroj unction --- p.3-8
Chapter 3.3 --- Oxygen annealing effect on LCMO/STON heteroj unction --- p.3-14
Chapter 3.4 --- Positive colossal Magnetoresistance in LCMO/STON heteroj unction --- p.3-16
References --- p.3-23
Chapter Chapter 4 --- Epitaxial PCMO/STON heterojunction
Chapter 4.1 --- Ohmic contact for PCMO thin films --- p.4-1
Chapter 4.2 --- PCMO charge ordering and magnetic phase transition --- p.4-9
Chapter 4.3 --- Four point I-V measurement of PCMO/STON heterojunction --- p.4-14
References --- p.4-16
Chapter Chapter 5 --- Epitaxial LCMO/PCMO/STON junction
Chapter 5.1 --- Tunneling junction fabrication --- p.5-1
Chapter 5.2 --- Structural characterizations --- p.5-2
Chapter 5.3 --- PCMO magnetic phase transition revealed by I-V measurement of LCMO/PCMO/STON tunneling junction --- p.5-3
Chapter 5.4 --- Energy band structure of perovskite manganites --- p.5-11
Chapter 5.4.1 --- Introduction to energy band of perovskite manganites and STON --- p.5-11
Chapter 5.4.2 --- Temperature dependent band structure of LCMO explained by diffusion voltage of LCMO/STON heterojunction --- p.5-18
References --- p.5-22
Chapter Chapter 6 --- Conclusions
Chapter 6.1 --- Conclusion --- p.6-1
Chapter 6.2 --- Future outlook --- p.6-3