Made available in DSpace on 2014-06-11T19:32:11Z (GMT). No. of bitstreams: 0 Previous issue date: 2002-08Bitstream added on 2014-06-13T20:03:18Z : No. of bitstreams: 1 cavalheiro_aa_dr_araiq.pdf: 6472595 bytes, checksum: e04161cc1c7b719e9fdf747d97469e9f (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Este trabalho se focaliza na obtenção da cerâmica relaxora PMN com temperatura de máxima constante dielétrica se situando próximo à temperatura ambiente, alta constante dielétrica e valores de perda dielétrica baixos. A influência dos dopantes potássio e lítio durante a síntese dos pós e o processamento da cerâmica PMN constitui uma grande contribuição para a pesquisa deste tipo de material. Os pós de PMN foram sintetizados utilizando a rota da columbita associada ao método de coprecipitação de chumbo. O monitoramento da formação da fase columbita foi acompanhado por DRX. O refinamento de estrutura, o cálculo do tamanho médio de cristalito e a microdeformação de rede foram executadas utilizando o método de Rietveld. Além disso, as amostras foram caracterizadas por TG/DTA, BET e MEV. Diferentemente do lítio, o potássio provoca a elevação da temperatura de formação da fase MgNb2O6 (MN), mas isto não interfere na obtenção do precursor monofásico até a concentração de 2,0%mol de dopante. Para pós de MN calcinados a 900ºC por 2 horas, a presença dos dopantes atenuam a microdeformação de rede e aumentam o tamanho médio de cristalito e, conseqüentemente ocorre a formação de partículas secundárias. Os valores de tamanho médio de cristalito das amostras de PMN dopadas com lítio, calcinadas a 800ºC por 2 horas, são maiores do que para as amostras dopadas com potássio. Nesta condição, a adição de lítio também acarreta crescimento de partículas e aglomeração dos pós. Durante a sinterização, as amostras dopadas com potássio apresentaram tamanho de grão menor e com menor faixa de distribuição de tamanhos, enquanto que para o lítio houve uma menor perda de massa. A mescla de pós permitiu obter maiores valores de densidade a verde, reduzir a perda de massa e obter uma cerâmica mais densa. A adição de,... / This work aims at getting the relaxor ceramic PMN with temperature of maximum dielectric constant close to room temperature, high dielectric constant and low dielectric loss values. The influence of the potassium and lithium additives during powder synthesis and processing of the PMN ceramic constitutes a great contribution to the research of this material type. The PMN powders were synthesized by using the columbite route associated to the lead co-precipitation method. The columbite phase formation was verified by XRD. The structure refinement, calculus of mean crystallite size and lattice microstrain were performed by using the Rietveld method. Furthermore, the samples were characterized by TG/DTA, BET and SEM. Differing from lithium, potassium increases the temperature of MgNb2O6 phase formation, however it does not hinder obtaining the monophasic precursor until 2mol% of additives. For columbite powders, burned at 900ºC during 2 hours, additive presence attenuates the lattice microstrain and increases the mean crystallite size and, consequently, the secondary particle formation occurs. The values of mean size crystallite for lithium doped-PMN samples burned at 800ºC during 2 hours are bigger than potassium ones. In this condition, the lithium doping causes particles growth and powder agglomeration. In sintering, the potassium doped-PMN samples showed smaller grain size and short range of size distribution, while the lithium doped ones showed lesser weight loss. The powder mixture allowed obtaining greater green density values, decreasing weight loss and getting a denser ceramic. Potassium addition reduces Km and Tm values, while the lithium addition, increases these values if compared to PMN. The utilization of LiNbO3 seeds reduces the weight loss and helps the ceramic densification. The seeded sample showed a diffuse phase transition more...(Complete abstract, click electronic access below)

Resumo: Este trabalho se focaliza na obtenção da cerâmica relaxora PMN com temperatura de máxima constante dielétrica se situando próximo à temperatura ambiente, alta constante dielétrica e valores de perda dielétrica baixos. A influência dos dopantes potássio e lítio durante a síntese dos pós e o processamento da cerâmica PMN constitui uma grande contribuição para a pesquisa deste tipo de material. Os pós de PMN foram sintetizados utilizando a rota da columbita associada ao método de coprecipitação de chumbo. O monitoramento da formação da fase columbita foi acompanhado por DRX. O refinamento de estrutura, o cálculo do tamanho médio de cristalito e a microdeformação de rede foram executadas utilizando o método de Rietveld. Além disso, as amostras foram caracterizadas por TG/DTA, BET e MEV. Diferentemente do lítio, o potássio provoca a elevação da temperatura de formação da fase MgNb2O6 (MN), mas isto não interfere na obtenção do precursor monofásico até a concentração de 2,0%mol de dopante. Para pós de MN calcinados a 900ºC por 2 horas, a presença dos dopantes atenuam a microdeformação de rede e aumentam o tamanho médio de cristalito e, conseqüentemente ocorre a formação de partículas secundárias. Os valores de tamanho médio de cristalito das amostras de PMN dopadas com lítio, calcinadas a 800ºC por 2 horas, são maiores do que para as amostras dopadas com potássio. Nesta condição, a adição de lítio também acarreta crescimento de partículas e aglomeração dos pós. Durante a sinterização, as amostras dopadas com potássio apresentaram tamanho de grão menor e com menor faixa de distribuição de tamanhos, enquanto que para o lítio houve uma menor perda de massa. A mescla de pós permitiu obter maiores valores de densidade a verde, reduzir a perda de massa e obter uma cerâmica mais densa. A adição de,...(Resumo completo, clicar acesso eletrônico abaixo) / Abstract: This work aims at getting the relaxor ceramic PMN with temperature of maximum dielectric constant close to room temperature, high dielectric constant and low dielectric loss values. The influence of the potassium and lithium additives during powder synthesis and processing of the PMN ceramic constitutes a great contribution to the research of this material type. The PMN powders were synthesized by using the columbite route associated to the lead co-precipitation method. The columbite phase formation was verified by XRD. The structure refinement, calculus of mean crystallite size and lattice microstrain were performed by using the Rietveld method. Furthermore, the samples were characterized by TG/DTA, BET and SEM. Differing from lithium, potassium increases the temperature of MgNb2O6 phase formation, however it does not hinder obtaining the monophasic precursor until 2mol% of additives. For columbite powders, burned at 900ºC during 2 hours, additive presence attenuates the lattice microstrain and increases the mean crystallite size and, consequently, the secondary particle formation occurs. The values of mean size crystallite for lithium doped-PMN samples burned at 800ºC during 2 hours are bigger than potassium ones. In this condition, the lithium doping causes particles growth and powder agglomeration. In sintering, the potassium doped-PMN samples showed smaller grain size and short range of size distribution, while the lithium doped ones showed lesser weight loss. The powder mixture allowed obtaining greater green density values, decreasing weight loss and getting a denser ceramic. Potassium addition reduces Km and Tm values, while the lithium addition, increases these values if compared to PMN. The utilization of LiNbO3 seeds reduces the weight loss and helps the ceramic densification. The seeded sample showed a diffuse phase transition more...(Complete abstract, click electronic access below) / Orientador: Maria Aparecida Zaghete / Coorientador: Carlos de Oliveira Paiva Santos / Banca: Edson Roberto Leite / Banca: Ivair Aparecido dos Santos / Banca: Ruth Herta Goldschimidt Aliaga Kiminami / Banca: Wanda Cecília Las / Doutor

Orientador: Eudes Borges de Araújo / Resumo: Filmes finos de Pb0,91La0,09(Zr0,65Ti0,35)O3 (PLZT) foram preparados sobre substratos Pt/TiO2/SiO2/Si(100), usando um método químico baseado no processo Pechini, com objetivo de estudar a supressão da fase pirocloro e a estabilização da fase perovskita. Pós de PLZT preparados por reação do estado sólido foram utilizados como principal fonte de íons Pb2+, La2+, Zr4+ e Ti4+ pela dissolução em solução ácida. A obtenção de resinas poliméricas estáveis com diferentes excessos de chumbo foi possível preparando-se separadamente as resinas de PLZT e PbO seguido de posterior mistura e homogeneização à temperatura ambiente. / Abstract: Pb0,91La0,09(Zr0,65Ti0,35)O3 (PLZT) thin films were prepared on Pt/TiO2/SiO2/Si(100) substrates by using a chemical method based on Pechini process to study the pyrochlore phase suppression and to stabilizing the perovskite phase. PLZT powders prepared by solid state reaction were used as source of Pb2+, La2+, Zr4+ and Ti4+ ions by its dissolution in acid solution. / Doutor

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Submitted by BACUS DE OLIVEIRA NAHIME null (bacusbn@gmail.com) on 2016-05-06T14:46:19Z No. of bitstreams: 1 Tese-Defesa-Final.pdf: 6832844 bytes, checksum: 4d6ea59ca8f13d248ccfc2acec9b95d2 (MD5) / Approved for entry into archive by Felipe Augusto Arakaki (arakaki@reitoria.unesp.br) on 2016-05-09T19:02:12Z (GMT) No. of bitstreams: 1 nahime_bo_dr_ilha.pdf: 6832844 bytes, checksum: 4d6ea59ca8f13d248ccfc2acec9b95d2 (MD5) / Made available in DSpace on 2016-05-09T19:02:12Z (GMT). No. of bitstreams: 1 nahime_bo_dr_ilha.pdf: 6832844 bytes, checksum: 4d6ea59ca8f13d248ccfc2acec9b95d2 (MD5) Previous issue date: 2016-04-01 / Programa de Capacitação dos Servidores do Instituto Federal de Educação, Ciência e Tecnologia Goiano / Filmes finos de Pb0,91La0,09(Zr0,65Ti0,35)O3 (PLZT) foram preparados sobre substratos Pt/TiO2/SiO2/Si(100), usando um método químico baseado no processo Pechini, com objetivo de estudar a supressão da fase pirocloro e a estabilização da fase perovskita. Pós de PLZT preparados por reação do estado sólido foram utilizados como principal fonte de íons Pb2+, La2+, Zr4+ e Ti4+ pela dissolução em solução ácida. A obtenção de resinas poliméricas estáveis com diferentes excessos de chumbo foi possível preparando-se separadamente as resinas de PLZT e PbO seguido de posterior mistura e homogeneização à temperatura ambiente. / Pb0,91La0,09(Zr0,65Ti0,35)O3 (PLZT) thin films were prepared on Pt/TiO2/SiO2/Si(100) substrates by using a chemical method based on Pechini process to study the pyrochlore phase suppression and to stabilizing the perovskite phase. PLZT powders prepared by solid state reaction were used as source of Pb2+, La2+, Zr4+ and Ti4+ ions by its dissolution in acid solution. / Programa de Capacitação dos Servidores do Instituto Federal de Educação, Ciência e Tecnologia Goiano, aprovado pela Resolução nº 028/2010 de 23/11/2010

En relation avec le désordre de leur structure, les composés relaxeurs révèlent une dualité entre les échelles locale et globale. L'ordre polaire qui se développe localement ne se manifeste pas à l'échelle globale, la structure globale demeurant cubique. Bien que pertinente au vu de ses capacités à saisir la dualité d'échelle, une incorporation directe de la symétrie locale à l'appareil d'étude des relaxeurs reste absente. C'est autour de cette lacune que s'articule la thèse, en ce qu'elle constitue une implémentation explicite de la symétrie locale dans l'Hamiltonien effectif. Elle porte sur l'analyse du rôle de la symétrie locale à sous-tendre l'ordre locale dont les propriétés macroscopiques émergent. Une question sous-jacente s'adjoint à ces considérations et concerne la possible formulation du problème d'un point de vue topologique / Concomitantly with lattice disorder, there is a discrepancy between local and global scales in relaxor ferroelectrics, in that structural distortions occurring at the local scale are not reflected in the average global structure which remains cubic. There is an absence of direct implementation of the local symmetry in the modeling of relaxors, despite its considerable, but often unacknowledged, ability to encode local features. Central to the thesis is an explicit account for local gauge symmetry within the first-principles-derived effective Hamiltonian approach. The thesis thus aims to consider how an extended symmetry allowing independent transformations at different points in space can effectively bridge local features and macroscopical properties. An underlying question the thesis also seeks to answer is whether the disorder-induced non-trivial interplay between local and global scales can be described from a topological point of view

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The present research work mainly focuses on the fabrication of 0.85PMN-0.15PT thin film relaxor ferroelectrics for energy harvesting applications. Chapter 1 gives a brief review about why energy harvesting is required and the different ways it can be scavenged. An introduction to relaxor ferroelectrics and their characteristics structural features are discussed. A brief introduction is given about charge storage, electrocaloric effect , DC-EFM and integration over Si substrate is discussed. Finally, the specific objectives of the current research are outlined. 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, Microstructural and physical property measurements is discussed. Chapter3 involves the optimization process carried out to contain a phase pure PMN-PT structure without any pyrochlore phase. The optimization process is an important step in the fabrication of a thin film as the quality of any device is determined by their structural and Microstructural features. XRD, SEM, AFM were used to characterize the observed phase formation in these films. The optimizing domain images of polycrystalline 0.85PMN-0.15PT thin films on La0.5Sr0.5CoO3/ (111) Pt/TiO2/SiO2/Si substrates deposited at different oxygen partial pressures are presented. The oxygen pressure has a drastic influence on the film growth and grain morphology which are revealed through XRD and SEM characterization techniques. The presence of oxygen vacancies have found to influence the distribution of polar nanoregions and their dynamics which are visualized using domain images acquired by DC-EFM In Chapter 7 the piezoelectric response of 0.85PMN-0.15PT thin films are studied due to the electric field induced bias. From this the d33 value is calculated. d33 value is an important parameter which determines whether a material is suitable for device application (PZT). But, for a device fabrication it is important to integrate them with Si wafer which is not a straightforward work .Hence, buffer layers are used to obtain a pure perovskite PMN-PT film. We have deposited 0.85PMN-0.15PT thin films of 500 nm on a SOI wafer and tried to investigate their piezoelectric application. Chapter 8 summarizes the present study and discusses about the future work that could give more insight into the understanding of the0.85PMN-0.15 PT relaxor ferroelectric thin film.

We developed a model to investigate the dielectric properties of the BaTiO₃ − Bi(Zn₁/₂Ti₁/₂)O₃ (BT-BZT) solid solution, which is a relaxor ferroelectric and exhibits long range disorder. The model uses ab initio methods to determine all polarization states for every atomic configuration of 2 x 2 x 2 supercells of BT-BZT. Each supercell is placed on a lattice with an Ising-like interaction between neighboring cell polarizations. This method allows us to consider long range disorder, which is not possible with ab initio methods alone, and is required to properly understand relaxor ferroelectric materials. We analyze the Monte Carlo data for a single lattice configuration using the multiple histogram method, and develop a modified histogram technique to combine data from multiple lattice configurations. Our calculated values of dielectric constant, specific heat, and polarization agree reasonably well with experiment. / Graduation date: 2012