Dissertations / Theses on the topic 'Relaxor perovskite'

Thesis (Ph. D.)--Ohio State University, 2005.
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This thesis set out to investigate lead free ferroic materials with perovskite and tungsten bronze type structures, primarily focussing on the relationship between composition, temperature and crystal structure. A combination of diffraction techniques were employed to investigate the crystal structures. Additionally, other techniques including XANES, SEM, TGA, DSC and ferroic peroperty measurements were also employed to further illuminate these compounds. The first system investigated was the defect perovskite Sr0.8Ti0.6-yZryNb0.4O3, 0.0 ≤ y ≤ 0.6. It was found that neutron powder diffraction data were essential for determining the phase boundary composition. Second order compositional and temperature phase transitions were observed. Increasing the zirconium content increased octahedral tilting and led to higher transition temperatures. Local ordering was determined to be highly probable and it was found that the presence of vacancies extended the range of the high symmetry phase. The second system investigated was the BaxSr3-xTi1-yZryNb4O15, 0.0 ≤ x ≤ 3.0, 0.0 ≤ y ≤ 1.0, tungsten bronze type system. Barium rich compositions were found to adopt a tetragonal structure, while strontium rich compositions adopted an orthorhombic structure. Increasing the zirconium content of samples was seen to make the orthorhombic phase persist further. A large focus was placed on determining the structure of Sr3TiNb4O15 as a model for all orthorhombic compounds. A new structural model was proposed for Sr3TiNb4O15 distinct from those previously published. All orthorhombic compositions were observed to undergo first order phase transitions to the tetragonal structure on heating. The barium and strontium atoms were found to order onto two crystallographically distinct A sites. It was found that the tungsten bronze tolerance factor could be used as a predictive tool for the crystal symmetry of these materials. All compounds in this system for which ferroelectric measurements were performed displayed ferroelectric hysteresis behaviour.

Nowadays BaTiO3 is considered as one of the most relevant environmental-friend ferroelectric and, thank to the chemical substitutions at the Ba2+ and/or Ti4+ sites, its properties are usually tailor to meet a big variety of devices and performance requirements. A classical example is the solid solution BaTi1-xMIVxO3, where M could be Sn, Zr, Hf, Ce etc., whose ferroelectric behavior shows an almost continuous variation with composition. The study of these compounds is then essential to improve their characteristics and make their suitable in more applications. Considering that their properties are deeply linked to the structure and especially to structural defects, average and local structural analyses are essential to better understand the origins of different polar behaviours and to have a real control on these materials. Despite this need, only BaTi1-xZrxO3 (BTZ) system, which is one of the most popular dielectrics used in multilayer ceramic capacitors, has been investigated in some detail. Although the similarity to BTZ suggests that BaTi1-xCexO3 (BTC) may be promising as lead free actuator materials, studies on this solid solution are almost limited. Thus in this research the BTC solid solution has been structurally investigated in order to provide knowledge lacks. Different ceramic samples with different doping amounts and different polar behaviours (from normal ferroelecric to relaxor via diffuse phase transition) have been investigated at different temperatures. In addition, taking into account the current tendency in miniaturized devices required in microelectronics, also chemical equivalent nano powders have been considered to explore not only doping effects, but also that of size. Pair Distribution Function (PDF) with different type of approaches (as carbox, biphasic and so on) has been employed coupled with TEM analysis and Raman spectroscopy. A complete description of that BaTi1-xCexO3 materials is given underlining links between polar behaviours, temperature, doping and size effects.

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Programa de Capacitação dos Servidores do Instituto Federal de Educação, Ciência e Tecnologia Goiano
Filmes finos de Pb0,91La0,09(Zr0,65Ti0,35)O3 (PLZT) foram preparados sobre substratos Pt/TiO2/SiO2/Si(100), usando um método químico baseado no processo Pechini, com objetivo de estudar a supressão da fase pirocloro e a estabilização da fase perovskita. Pós de PLZT preparados por reação do estado sólido foram utilizados como principal fonte de íons Pb2+, La2+, Zr4+ e Ti4+ pela dissolução em solução ácida. A obtenção de resinas poliméricas estáveis com diferentes excessos de chumbo foi possível preparando-se separadamente as resinas de PLZT e PbO seguido de posterior mistura e homogeneização à temperatura ambiente.
Pb0,91La0,09(Zr0,65Ti0,35)O3 (PLZT) thin films were prepared on Pt/TiO2/SiO2/Si(100) substrates by using a chemical method based on Pechini process to study the pyrochlore phase suppression and to stabilizing the perovskite phase. PLZT powders prepared by solid state reaction were used as source of Pb2+, La2+, Zr4+ and Ti4+ ions by its dissolution in acid solution.
Programa de Capacitação dos Servidores do Instituto Federal de Educação, Ciência e Tecnologia Goiano, aprovado pela Resolução nº 028/2010 de 23/11/2010

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

Nous avons synthetise et etudie la structure de composes perovskites ferroelectriques pbsc 1 / 2nb 1 / 2o 3, caracterisees par differents degres d'ordre sc/nb et par une stchiometrie differente sur le site du pb. Ces composes sont appeles relaxeurs : leur constante dielectrique est elevee avec une forte valeur sur une gamme de temperatures importante et presente un phenomene de dispersion en frequence. L'etude de l'ordre des cations sc/nb sur le site b par diffraction des rx et des neutrons est mise en relation avec les proprietes dielectriques : il existe toujours un ordre local a courte portee au sein des composes macroscopiquement desordonnes, de meme que l'ordre reste a moyenne portee dans le psn ordonne. La mise en ordre sur le site b a un effet sur la valeur du maximum de la constante dielectrique, alors que la non-stchiometrie (introduction de lacunes, substitution plomb/baryum) augmente fortement la diffusivite de l'anomalie dielectrique. Dans la phase paraelectrique, nos etudes par diffraction ont montre que les atomes de plomb n'occupent jamais leur position ideale cubique et sont statistiquement desordonnes de facon isotrope a des temperatures bien superieures a la temperature de transition. Nous avons montre le meme type de desordre dans la perovskite simple pbtio 3, desordre qui dans ce cas n'est present que juste au-dessus de la temperature de transition. Ce desordre est caracteristique des atomes de plomb car nous avons montre son absence dans batio 3 et basc 1 / 2nb 1 / 2o 3. La phase ferroelectrique rhomboedrique est semblable pour tous les composes de psn. Les deplacements cooperatifs des cations a et b s'averent etre semblables a ceux du pmn/pt, mais differents de batio 3, ainsi que ceux de la phase tetragonale

Les solutions solides (1-x)Na0,5Bi0,5TiO3 (NBT) – xCaTiO3 (CT) ont été étudiées par diffraction des rayons X, spectroscopie Raman, microscopie électronique à balayage, spectroscopie d’impédance et DSC. Ce sont des matériaux présentant la structure cristalline pérovskite. L’étude révèle la complexité mais aussi la richesse des phénomènes physiques dans cette famille de composés : les séquences des transitions de phases, l’influence du dopant Ca2+ sur les propriétés physico-chimiques du matériau, la relation étroite entre propriétés diélectriques et caractéristiques structurales. Des solutions solides (1-x)NBT – xCT, avec 0 ≤ x ≤ 1,00, ont été synthétisées par voie solide classique puis frittées selon une procédure spécifique dans un milieu confiné pour éviter toute perte de sodium et de bismuth. Les caractéristiques cristallines des solides obtenus imposent clairement de distinguer trois domaines suivant les valeurs de x. En effet, pour les valeurs croissantes de x et à la température ambiante, on observe un premier domaine (Région I, pour x ≤ 0,07) dans lequel le solide obtenu est une solution solide de structure cristalline, de groupe d’espace R3c, identique à celle de NBT pur. Pour les valeurs les plus élevées de x (Région II, pour x ≥ 0,15), le solide obtenu est une solution solide de structure cristalline, de groupe d’espace Pnma, identique à celle de CT pur. Enfin, entre ces deux domaines (Région III, 0,09 ≤ x ≤ 0,13), les solides obtenus sont biphasés, R3c + Pnma, en se limitant aux appellations des groupes d’espacé des phases formées. Dans la région I, lors du chauffage, la séquence des transitions de phases R3c → P4bm → Pm3m est mise en évidence; les températures des transitions se déplacent vers les plus basses températures quand la concentration en Ca2+ augmente. Les solides sont ferroélectriques à l’ambiante puis développent un caractère relaxeur, par coexistence de deux phases, avec l’augmentation de la température. Dans la région II, les solides révèlent un comportement relaxeur dès l’ambiante. Une transition de phase diffuse au sein de la phase orthorhombique Pnma est toutefois mise en évidence ; le solide passe d’un état relaxeur à un état paraélectrique tout en conservant, a priori, la même structure cristalline. Le phénomène de relaxation dans ces composés est expliqué par la formation de micros ou nanorégions polaires. La région III, quant à elle, est caractérisée par l’apparition d’une hystérésis thermique mise en évidence pour la première fois ; elle est expliquée par la relation entre la microstructure cristalline et les propriétés diélectriques. Enfin, l’ensemble de nos résultats a été regroupé dans un diagramme de phase original en composition et en température
The solid solutions (1-x)Na0,5Bi0,5TiO3 (NBT) – xCaTiO3 (CT) were studied by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, impedance spectroscopy and DSC. These materials have a perovskite crystalline structure. This study reveals not only the complexity but also the richness of physical phenomena in these compounds: phases transitions sequences, the Ca2+ effect on the physical-chemistry properties and the relation between dielectric properties and crystalline structure. Thereby, (1-x)NBT – xCT solid solutions (0 ≤ x ≤ 1.00) were synthesized by chemical solid route, then they were sintered by a particular procedure in order to avoid sodium and bismuth volatilization. The solid crystalline characteristics obtained prove clearly the necessity to distinguish three fields as a function of x values. First of all, for increasing x at room temperature, there is a first region so called region I (x ≤ 0.07), wherein the crystalline structure of solid solutions obtained has a space group R3c identical to that of pure NBT. For the highest values of x, (Region II, x ≥ 0.15), the solid obtained has a space group Pnma, identical to that of pure CT. Finally, between these two regions, (0.09 ≤ x ≤ 0.13), the solid solutions obtained are biphasic, R3c + Pnma, limited to appellations of the space groups formed phases. In region I, upon heating, phase transition sequence R3c → R3c + Pnma → Pnma was determined; the corresponding transition temperatures move to low values with increasing Ca2+ concentration. These solids are ferroelectric at room temperature and then develop a relaxor character, by coexistence of two phases, with increasing temperature. In region II, these solids reveal a relaxor behavior at room temperature. However, a diffuse phase transition within the orthorhombic phase Pnma has been identified; the solid changes from relaxor to paraelectric while maintaining the same crystal structure. This phenomenon was explained by the formation of micro or nano-polar regions. Region III, demonstrated for the first time, is characterized by thermal hysteresis, and explained by the relation between crystalline microstructure and dielectric properties. Finally, all our results were assembled in an original phase diagram as a function of concentration of Ca2+ dopant and temperature

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
O presente trabalho descreve os estudos realizados para a síntese de filmes ferroelétricos ultrafinos de Pb(Mg1/3Nb2/3)O3 (PMN) e o estudo sistemático da cinética de cristalização deste material visando a obtenção de filmes monofásicos. Os filmes foram produzidos a partir da modificação de um método químico baseado em precursores óxidos. A obtenção dos filmes de PMN se deu através de uma técnica de duplo estágio, que possibilita maior controle na supressão de fases pirocloro, e da técnica via Método dos Precursores Óxidos (MPO), através da reação direta dos óxidos. Filmes de PMN foram preparados sobre substratos Si(100) com diferentes números de deposições. Esses filmes foram submetidos a tratamentos térmicos entre 400oC e 800ºC, em forno convencional, sob diferentes condições de preparo. A estrutura dos filmes foi investigada pela técnica de difração de raios-X e refinamentos da estrutura pelo método de Rietveld. Os resultados apresentaram uma coexistência da fase pirocloro Pb1.86Mg0.24Nb1.76O6.5 e da fase perovskita Pb(Mg1/3Nb2/3)O3 (PMN) nos filmes preparados via rota da Columbita e a supressão da fase prirocloro nos filmes preparados pelo método MPO. Um estudo da morfologia por MEV indicou a preparação de filmes com boa homogeinidade e espessura média de 150nm Os resultados obtidos neste projeto indicam que a estabilização da fase perovkita do PMN e a supressão da fase pirocloro está relacionada a uma combinação particular de parâmetros tais como tempo e temperatura de cristalização e a adição de excessos de MgO e PbO a estequiometria.
The present work describes the studies for the synthesis of ultrathin ferroelectric films of Pb(Mg1/3Nb2/3)O3 (PMN) and the systematic study of the crystallization kinetics of this material aimed at obtaining singlephase films. The films were produced from the modification of a chemical method based on oxide precursors. The obtention of the PMN films made by a technique of double stage, that allows greater control in the suppression of pyrochlore phases, and by technique via Oxide Precursors Method(OPM), through a direct reaction of the oxides. PMN films were prepared on Si(100) substrates with different numbers of depositions. These films were subjected to thermal treatments between 400ºC and 800°C, in conventional oven, under different preparation conditions. The structure of the films was investigated by the technique of X-ray diffraction and the structures refinements by the Rietveld method. The results showed a coexistence of pyrochlore phase Pb1.86Mg0.24Nb1.76O6.5 and perovskite phase Pb(Mg1/3Nb2/3)O3(PMN) in the films prepared via Columbita route and suppression of pyrochlore phase in films prepared by the OPM method. A study of morphology by SEM indicated the preparation of films with good homogeneity and medium thickness of 150 nm. The results obtained in this project suggest that the stabilization of PMN phase perovkite and the suppression of the pyrochlore phase is related to a particular combination of parameters such as time and temperature of crystallization and the addition of excess of MgO and PbO in the stoichiometry.

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Financiadora de Estudos e Projetos
Lead titanate zirconate modified with lanthanum, or PLZT, is one the most ferroelectric compounds utilized in electronic devices, due to its versatility and low production costs in comparison with single-crystalline materials. When adequately prepared, this system presents good optical (high optical transmission) properties, in the visible and near infrared range, and can be electro-optically characterized. Recently, in the end of 90 s, it was verified its high potential as host of photoluminescent ions, as the lanthanide (rare-earth) family. The possibility to use its electro-optic properties (due to its ferroelectric characteristics) and its photoluminescent properties (achieved by the doping process) together ,enlarges the range of application of this system. In this way, the electro-optical characterization of doped PLZT ceramics becomes essential, besides the photonic characterization. In this work, the Senarmont compensator method for electro-optical characterization, or dynamic method, was instrumented, and the values of the induced (due to the quadratic electrooptic effect, Kerr) and permanent (due to the linear electro-optic effect, Pockels) birefringence were determined as a function of the temperature, wave-length and electric-field frequency, of the rare-earth (Nd2O3, Ho2O3, Er2O3, Tm2O3 e Yb2O3) doped PLZT, with La/Zr/Ti=9/65/35, ceramics. The results shown a relationship between of the electro-optic (electro-optic coefficients, or birefringence values) and the dielectric, ferroelectric and structural properties (studied in others works) of the ceramics, that were related with the site occupancy and the structural defects due to the aliovalent dopant. It also can be identified two distinct birefringence dependence as a function of the electric field, for the same electro-optic effect (Kerr, or Pockels), identified as a function of the doping process. In the case of electro-optical characterizations in function of the variable frequency, was observed an agreement with the characterization ferroelectric results made in other works in GCFerr, being evidenced the reduction of electro-optical properties with increasing frequency, where if it observed the occurrence of anomalies in the Pockels response with direct influence on the response Kerr. The characterization as a function of wavelength showed the occurrence of two types of behavior depending on the dopant ion used, being one of them the reduction of the values of birefringence with increasing wavelength (the samples pure and doped ions neodymium (Nd) and ytterbium (Yb)), with a tendency to expected behavior in the literature, however, in the second was seen irregular increase birefringence with increase wavelength (for samples doped with ions holmio ( Ho), erbium (Er) and thulium (Tm),not existing relation with to the theoretical models adopted. In relation the characterization as a function of temperature, this was carried through in a temperature interval that understood the characteristic temperatures of systems relaxores (freezing temperature (TF), the maximum dielectric permittivity (TM (e)) and Burns (TB)), except for the sample doped with neodymium ions, whose freezing temperature is below interval worked. By the curve of birefringence (Δn) as a function of temperature was possible to determine the temperature of maximum birefringence for each of the samples, correlated them with each other. Through the curve (d Δn / dt) vs. T was possible to identify a relationship between the maximum variations, positive and negative birefringence with the temperature characteristics TF and TB.
Entre os sistemas ferroelétricos, o sistema titanato zirconato de chumbo modificado com lantânio (PLZT) é um dos mais amplamente utilizados em dispositivos eletrônicos, dada sua versatilidade em aplicações e relação de custo quando comparado aos materiais monocristalinos utilizados nessa mesma área. Quando preparado pelo devido método de síntese, apresenta excelentes propriedades óticas (altos valores de transmissão ótica) desde a região do visível ao infravermelho próximo, possibilitando uma adequada caracterização de suas propriedades óticas e eletro-óticas. Recentemente, a partir do final da década de 90, foi verificada sua alta potencialidade como matriz hospedeira para íons fotoluminescentes, como os da família dos lantanídeos (ou terras-raras). A possibilidade do uso conjunto das propriedades eletro-óticas (dado seu caráter ferroelétrico) e de suas propriedades luminescentes (devido à incorporação de dopantes laser-ativos) aumentou ainda mais a possibilidade de aplicação desses materiais. Desse modo, a caracterização eletro-ótica das cerâmicas de PLZT dopado torna-se indispensável, além de sua caracterização fotônica. Sendo assim, neste trabalho foi instrumentado um sistema de caracterização eletro-ótica, utilizando o método do compensador Senarmont, também conhecido como método dinâmico, para determinar os valores da birrefringência induzida (devido ao efeito eletro-ótico quadrático, Kerr) e a permanente (devido ao efeito eletro-ótico linear, Pockels) em função da temperatura, comprimento de onda e frequência do campo elétrico de prova para composições cerâmicas de PLZT na razão La/Zr/Ti=9/65/35, dopadas com os óxidos terras-raras Nd2O3, Ho2O3, Er2O3, Tm2O3 e Yb2O3, na quantidade de 1,0% em peso. Os resultados mostraram que há uma relação entre as propriedades eletro-óticas encontradas (seja na forma de valores dos coeficientes eletro-óticos, ou na variação da birrefringência) com as propriedades dielétricas, ferroelétricas e estruturais (já observadas em outros trabalhos do grupo de pesquisa no qual esta dissertação foi realizada) das cerâmicas que, por sua vez, foram relacionadas com o tipo de ocupação e de defeitos gerados devido à incorporação dos dopantes. Além disso, foi possível observar que para uma mesma composição pode ocorrer a presença dos dois tipos de efeitos eletro-óticos - Kerr e Pockels - com proporções distintas em função do tipo de dopante. Através desse método, para esse conjunto de amostras, também foi possível identificar dois tipos distintos de variações da birrefringência em função do campo elétrico para um mesmo efeito eletro-ótico (Kerr, ou Pockels), que também puderam ser associados com o tipo de ocupação dos dopantes. Em se tratando das caracterizações eletro-óticas em função da variável frequência, foi observada uma concordância com os resultados da caracterização ferroelétrica, realizada em outros trabalhos no GCFErr, sendo evidenciada a redução das propriedades eletro-óticas com o aumento da frequência, em que se observou a ocorrência de anomalias na resposta Pockels com influência direta na resposta Kerr. A caracterização como uma função do comprimento de onda mostrou a ocorrência de dois tipos de comportamentos, dependendo do íon dopante utilizado, sendo um deles a redução dos valores da birrefringência com o aumento do comprimento de onda (caso das amostras pura e dopadas com os íons neodímio (Nd) e itérbio (Yb)), havendo certa tendência ao comportamento previsto em literatura, no entanto, no segundo caso foi constatado o aumento irregular da birrefringência com o aumento do comprimento de onda (caso das amostras dopadas com os íons holmio (Ho), érbio (Er) e túlio (Tm), não havendo relação com os modelos teóricos adotados. Quanto à caracterização em função da temperatura, esta foi realizada em um range de que compreendeu as temperaturas características de sistemas relaxores (de freezing (TF(e)), máxima permissividade dielétrica (TM(e)) e Burns (TB(e))), exceto para a amostra dopada com o íon neodímio, cuja TF(e) estava abaixo do intervalo considerado. Através da curva de birrefringência (Δn) em função da temperatura foi possível determinar a temperatura de máxima birrefringência para cada uma das amostras, correlacionado-as entre si. Através da curva de (dΔn/dt) vs. T, foi possível constatar uma relação entre as máximas variações, positiva e negativa, da birrefringência com as temperaturas características TF e TB.

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This study revisits the lanthanum-modified lead zirconate titanate ferroelectric relaxor system (PLZT) by investigating its electro-optical properties, particularly the variation of birefringence induced by electrical field, n(E). The thermal evolution of n(E), obtained by the Kerr (quadratic) and Pockels (linear) electro-optical effects, was considered in the verification of possible critical temperatures predicted for the transitions between the paraelectric (PE), ergodic ferroelectric relaxor (EFR), non-ergodic ferroelectric relaxor (NEFR), and normal ferroelectric (FE) states. Such temperatures identify the regions that separate different correlation states (static and dynamic) from the polar nano-regions (PNR) present in these materials. This work made use of ceramics La/Zr/Ti = 9/65/35, which are located on the tricritical point of the PZLT phase diagram. The effect of doping with 1% weight of rare-earth oxides (Nd, Ho, Er, Tm e Yb) upon the relaxor behaviour was also investigated. The undoped material was used as a reference system in the elaboration of a protocol for data collection and treatment, which included the results of ferroelectric, dielectric and pyroelectric measurements. The n(E) results obtained for the quadratic response (Kerr effect) as a function of temperature were suitable for determining the freezing temperature (Tf) associated to the FE-FRE transition or to the FRE-FRNE transition, as well as the temperature associated to the maximum electrical permittivity (Tε′m), and the Burns temperature (TB) associated to the FRE-PE transition. Conversely, the dependence of n(E) to linear response (Pockels effect) as a function of temperature proved sensitive for determining the characteristic temperature T*, which indicates the initial temperature for a correlated state of short and mid-range NRP reach during cooling of the material. All of these characteristic temperatures could be determined for the doped PLZT system as well, and the same behaviours were observed for the Kerr and Pockels electro-optical responses. It is worth noting that this is the first time the n(E) linear effect response is applied to the analysis of this system. However, the transition intervals between polar and non-polar states suffered changes according to rules associated to the difference between the ionic radii of rare-earth and the cation that had been replaced in the crystal structure. Although the ferroelectric, electric, dielectric, pyroelectric, and electro-optical properties of the PLZT system were clearly affected by doping, no significant changes in the relaxor behaviour could be observed.
Este trabalho revisita o sistema ferroelétrico relaxor titanato zirconato de chumbo modificado com lantânio (PLZT) a partir de investigações de suas propriedades eletro-ópticas, particularmente da variação da birrefringência induzida por campo elétrico, n(E). Foi considerada a evolução térmica de n(E), obtida pelos efeitos eletro-ópticos Kerr (quadrático) e Pockels (linear), para a determinação (ou validação) de possíveis temperaturas críticas, características de transições entre os estados paraelétrico (PE), ferroelétrico relaxor ergódico (FRE), ferroelétrico relaxor não-ergódico (FRNE) e ferroelétrico normal (FE), previstas para sistemas ferroelétricos relaxores. Tais temperaturas identificam as regiões que separam diferentes estados de correlação (estática e dinâmica) das nano-regiões polares (NRP) presentes nesses materiais. Para o estudo, foram utilizadas cerâmicas da composição La/Zr/Ti = 9/65/35, nomeado PLZT, que se localiza no ponto tricrítico do diagrama de fases. O efeito da dopagem neste sistema, com 1% em peso de óxidos de elementos terras-raras (Nd, Ho, Er, Tm e Yb) sobre o comportamento relaxor, também foi discutido. Como sistema de referência, foram utilizados protocolos de aquisição e tratamento de dados, que incluíram também resultados de medidas ferroelétricas, dielétricas e piroelétricas. Verificou-se que os resultados de n(E) para a resposta quadrática (efeito Kerr), em função da temperatura, permitem a determinação da temperatura de freezing (Tf), associada ora à transição FE-FRE e ora à FRE-FRNE; da temperatura associada àquela de máximo da permissividade elétrica (Tε′m); e da temperatura de Burns (TB), associada à transição FRE-PE. Já a dependência de n(E), para a resposta linear (efeito Pockels), com a temperatura, permite a determinação da temperatura característica T*, indicadora do ponto inicial de um estado correlacionado de curto e médio alcance das NRP, durante o resfriamento do material. Trata-se da primeira vez em que a resposta n(E) do efeito linear é aplicada à análise de sistemas como esse. Todas as temperaturas características puderam ser determinadas no sistema dopado, sendo observadas as mesmas peculiaridades para as respostas eletro-ópticas Kerr e Pockels. Contudo, os intervalos para as transições entre os estados polar e não-polar deslocaram-se, seguindo regras associadas à diferença entre o raio iônico do terra-rara em relação ao do cátion substituído na rede cristalina. Embora a dopagem tenha alterado as propriedades ferroelétricas, elétricas, dielétricas, piroelétricas e eletro-ópticas do sistema PLZT, em geral não foram observadas mudanças no comportamento relaxor.

The group of materials with ABO3 type perovskite structure are very important due to their attractive electrical and magnetic properties for technological applications and have been studied in the form of single crystals, bulk polycrystalline materials and thin films. Recently, efforts have been made to synthesize and understand the growth of ABO3 type perovskite nanostructures because of their distinctive physical properties and potential applications in the nanodevices. The primary aim of the present thesis is to synthesize the perovskites at nano-scale, with zero-dimension (0D), and one-dimension (1D) configurations. Basic work was carried in terms of synthesis – structure – composition correlation. Due to the small nature of the synthesized materials, few attempts were done to examine the physical properties, but to a limited extant. Efforts were also done to emphasize the structural behavior of nano perovskite in comparison with their bulk counterparts. Chapter 1 provides a brief introduction to perovskite materials and nanostructures, their technological applications and the fundamental physics involved. A brief review of the perovskite nanostructures both from fundamental science and technological point of view is provided. Finally the specific objectives of the current research are outlined. Chapter 2 deals with the experimental studies carried out in this thesis. It describes the methods used for the synthesis, experimental set up and the basic operation principles of various structural and physical characterizations such as X-ray diffraction (XRD), thermal analysis, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM), compositional analysis (EDX), focused ion beam (FIB), electrical and magnetic studies of the materials prepared. Chapter 3 describes the fabrication of porous anodic aluminum oxide (AAO) templates with different pore size, basic steps for synthesis of nanotubes and the possible growth mechanism of nanotubes in the AAO template. In chapter 4, we report the synthesis of ferroelectric Ba1-xSrxTiO3 (x = 0.0, 0.3) nanoparticles (diameter range: 20-40nm) and Ba1-xSrxTiO3 (x = 0.0, 0.4) nanotubes with diameter about 200nm by the sol-gel method. The Ba1-xSrxTiO3 nanostructures so obtained were characterized by number of techniques, including FE-SEM, XRD, DTA/TGA, FTIR spectroscopy, TEM, HRTEM as well as EDX and SAED. Formation of Y-junctions and multi-branches in Ba1-xSrxTiO3 nanotubes were also observed. The wall of the nanotubes were found to be made of randomly oriented nanoparticles which were confirmed from the HRTEM image. The average thickness of the wall of the nanotubes was found around 15(±5) nm and nanoparticles consisting the wall were found to be in the range of 5-10nm. Diffused phase transition (cubic to tetragonal), shifted to lower temperature side and leaky ferroelectric P–E loops were observed in Ba1-xSrxTiO3 (x = 0.0) ceramic prepared from nanoparticles. Curie temperature was observed at 120oC in the BT nanotube array as confirmed by the dielectric study. The P–E loops of as-prepared Ba1-xSrxTiO3 (x = 0.0) nanotube array were also measured and the hysteresis clearly demonstrates the room temperature ferroelectricity in the as prepared nanotubes, indicating these nanotube array is potential media as ferroelectric information storage. In chapter 5, we report the synthesis of single crystalline nanoparticles and polycrystalline nanotubes of Pb0.76Ca0.24TiO3 (PCT24) by sol-gel processing and characterized by various techniques. The crystallinity and phase purity of the PCT24 nanoparticles and nanotubes were confirmed by the XRD and SAED pattern. Compositional homogeneity and their crystalline structure confirms the formation of the tetragonal perovskite phase. The wall of the nanotubes was found to be made of nanoparticles which were confirmed from the HRTEM analysis. The average thickness of the wall of the nanotubes was found around 20nm and nanoparticles consisting the wall were found to be in the range of 5-8nm. Formation of some single crystalline PCT24 nanorods was also observed as confirmed by SAED and HRTEM analysis. Formations of Y-junctions and multi-branches in this complex functional oxide were observed. Dielectric measurements shows the diffuse phase transition and frequency dependence of Tm (temperature at which real part of dielectric constant shows maxima) suggesting the relaxor type behavior in the PCT24 ceramic prepared from nanoparticles. Polarization study was carried out on PCT24 nanotube array, which shows the ferroelectric nature at room temperature. Chapter 6 reports the synthesis and studies of PbZrO3 (PZ) nanoparticles and PbZr1-xTixO3 for x = 0.0, 0.48 and 1.0 nanotubes. PZ nanoparticles were prepared by a novel sol-gel method based on diol-based solution. Initially, PZ was crystallized with some intermediate m-Z and t-Z phases at 400-550oC and start transforming to orthorhombic at around 600oC and then finally transformed into pure orthorhombic PZ phase at about 700oC. XRD and TEM confirmed the nanocrystalline nature of PZ particles. Curie temperature in the PZ ceramic prepared from PZ nanoparticles was observed around at 205oC, which is lower as compared to the bulk (233oC). P–E hysteresis loops of PZ ceramic prepared from nanoparticles were measured at different applied voltages and single ferroelectric loops of leaky nature were observed rather than antiferroelectrics. The lead zirconate nanoparticles produced may have potential applications as materials used in microelectronics and microelectromechanical systems. PbZr1-xTixO3 for x = 0.0 (PZ), 0.48 (PZT48) and 1 (PT) nanotubes were fabricated by sol-gel method within the closely packed porous alumina templates and characterized by various techniques. The crystallinity of the PZ, PZT48 and PT nanotubes were confirmed via XRD and SAED studies. EDX analysis demonstrated that stoichiometry was formed. Formation of Y-junctions in this complex functional oxide was also observed. The wall of the nanotubes was found to be made up of randomly oriented nanoparticles, which were confirmed by the HRTEM studies and also by a typical SEM image. The average thickness of the wall of the nanotubes was found to be around 10-20nm and nanoparticles consisting the wall was found to be in the range of 3 – 8nm. The Curie temperature was observed at 220oC in the PZ nanotube array. For the first time, PLD has been employed for the synthesis of lead zirconate nanotubes using AAO template. Well-registered arrays of these nanotubes could function as three dimensional (3D) device elements in miniaturized ferroelectric random access memory (FRAM). In chapter 7, we report the synthesis of single crystalline 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 (PMN-PT) nanoparticles. PMN-PT nanoparticles were developed by a novel sol-gel method based on diol route. After partial calcination at 450oC/1h, PMN-PT powder morphology started transforming from pyrochlore to perovskite phase. It is interesting to note that this partially crystallized PMN-PT powder was unstable under electron beam and generated freestanding lead nanoparticles after absorbing energy from a focused electron beam. PMN-PT powder annealed at 700°C was fully transformed to perovskite phase and was stable under electron beam. XRD calculations and TEM imaging confirmed the nanocrystalline nature of PMN-PT particles. Magnetic measurements on PMN-PT nanoparticles prepared at 650 and 750oC show room temperature ferromagnetic hysteresis, whereas the bulk or the agglomerated particles show diamagnetic behavior. With an increase of annealing temperature or the particle size the magnetic moment decreases. PMN-PT nanotubes with diameter about 200nm were fabricated successfully by the sol-gel method based on diol route within the closely packed porous nanochannel alumina templates. Phase purity and crystalline perovskite phase formation of PMN-PT nanotubes were confirmed by the XRD and SAED pattern. EDX analysis demonstrated that stoichiometry was formed within accepted limit. The wall of the nanotubes was found to be made of nanoparticles which were confirmed from the HRTEM analysis. The average thickness of the wall of the nanotube was found around 20 nm and nanoparticles consisting the wall were found to be in the range of 10-20 nm. Since electroceramic materials are following a similar trend to miniaturization as conventional semiconductors, the synthesis of nanosized oxidic building blocks is moving into the focus of scientific and technological interest. Ferroelectrics are promising class of materials for the fabrication of electronic devices, as they are already an integral part of modern nanotechnological operations. Chapter 8 deals with the synthesis and properties of BiFeO3 (BFO) nanoparticles and nanotubes. Single crystalline BFO nanoparticles of different size and polycrystalline BFO nanotubes were prepared by sol-gel method. As prepared nanostructures were characterized by various techniques such as XRD, TGA-DTA, FTIR, scanning electron microscope (SEM), transmission electron microscope (TEM), selected-area electron diffraction (SAED), high resolution TEM and energy-dispersive X-ray spectroscopy (EDX). The crystallinity and phase purity of the BFO nanoparticles and nanotubes were confirmed by the XRD, SAED pattern and HRTEM analysis. Compositional homogeneity and their crystalline structure confirms the formation of the rhombohedrally distorted perovskite phase. EDX analysis demonstrated that stoichiometric BiFeO3 was formed within accepted limit. The HRTEM analysis confirmed that wall of the BFO nanotubes was made of nanoparticles, which were randomly oriented in the wall. The average thickness of the wall of the nanotubes was found to be around 15 nm and nanoparticles consisting the wall were found to be in the range of 3-6nm. Formation of Y-junctions in this complex functional oxide was observed. Magnetic measurements show clearly the enhancement of ferromagnetism in BFO nanotubes and ferroelectric loops were also observed in these nanotubes, that indicates the multiferroic nature of these nanotubes. BFO nanostructures at a large scale might be important for many applications such as memory elements in nanoscale devices in future. Chapter 9 reports the synthesis of a series of crystalline La1-xCaxMnO3 (x = 0, 0.3, 0.5, 0.7) nanoparticles with average diameter about 20 nm by an improved sol-gel method. The crystallinity and phase formation of as prepared nanoparticles was confirmed via XRD, SAED and HRTEM studies. EDX analysis demonstrated that desired stoichiometric was formed. Magnetic characterization reveals that the PM-FM transitions (Tc) occurs around at 205, 235, 235 and 230 K for x = 0, 0.3, 0.5, 0.7, respectively. The strong irreversibility between zero field cooling (ZFC) and field cooling (FC) magnetization curves, a cusplike peak in ZFC curve and unusual shape of M versus H loop at T = 5 K gives strong support for surface spin glass behavior. The highly stable charge ordering state in bulk manganites is suppressed, while the ferromagnetism is enhanced in these nanoparticles (x = 0.5 and 0.7). La0.7Ca0.3MnO3 were fabricated by sol-gel method within the closely packed porous alumina templates. The wall of the nanotubes was found to be made up of randomly oriented nanoparticles (8-12nm) as confirmed by HRTEM studies. The strong irreversibility between ZFC and FC magnetization curves as well as a cusplike peak in ZFC curve gives strong support for surface spin glass behavior. Magnetization value as obtained from M-H loop was about 28.5% of expected value, suggesting the existence of a magnetic dead layer, which avoids the propagation of exchange interaction between magnetic grains. The PM-FM transition was observed at 235 K. Chapter 10 gives the summary and conclusions of the present study and also discusses the possible future work that could after more insights into the understanding of the perovskite nanostructures. Highlight of the present work (i) Successful growth of nanostructures in both particles and tube forms, and study of their structure – composition correlations. (ii) Present work could optimize the necessary chemistry to successfully grow nanoparticles and nanotubes of various perovskite compositions. (iii) Successful studies of physical properties of nanoparticles and nanotubes, ofcourse, to a limited extent. However the properties observed in the present nanostructures have a strong indication of nonlinear phenomena similar to their bulk counterparts. (iv) It was reported in the literature, the observation of ferromagnetic behavior in several nonmagnetic compositions at nano-scale. Surprisingly, similar ferroelectric behavior was noticed even in our perovskite complex oxides such as relaxors (PMN-PT). A clear interaction of magnetic spin and an electric dipole was evident in these oxides such as relaxors and also multiferroics at nano-scale (~10-20 nm). (v) In ferromagnetic compositions such as LCMO, a very interesting spin-glass type behavior was observed.