No description available.

Lead-based and lead-free ferroelectric ceramic materials were prepared at low sintering temperatures with particular regard to their applications in thick film piezoelectric components. This project is focused on the development of processing methods and novel compositions to be used for thick film production by electrophoretic deposition (EPD) on heat-resistant alloys. Lead-based glasses and an oxide mixture (LiCO3, Bi2O3 and CuO), denoted LBCu, with low melting points were used as sintering aids for lanthanum-doped lead zirconate titanate (PLZT) ceramics. The required temperature to achieve dense ceramics was reduced from 1250 to 950 °C. It was found that the highest ferroelectric properties were obtained by the use of LBCu in comparison with those incorporating glass additives due to the shielding effect of the glass phase between the ferroelectric grains. However, the results of thick film preparation shown that the samples with glass additives were much smoother and relatively free of cracks up to 1000 ÂoC. In terms of lead-free ceramics, novel compositions were prepared, based on (Ba,Ca)(Zr,Ti)O3-(K0.5Bi0.5)TiO3 (BCZT-KBT) solid solutions having various Ca and Zr contents. The new solid solutions exhibited interesting features comprising core-shell type microstructures and relaxor ferroelectric behaviour in addition to reduced sintering temperatures and higher Curie point compared with BCZT ceramics. The required sintering temperature reduced to 1125 °C at 65% KBT, in comparison with 1500 °C for pure BCZT. The results showed that the compositional heterogeneity in the shell regions was reduced by air quenching, relative to that of the slow-cooled state, due to the retention of the more chemically-homogeneous high temperature state by the quenching process. The improvements were evident in increased polarisation, piezoelectric coefficient and depolarisation temperature values. However, the slow-cooled samples exhibited high reversible strain levels due to the presence of polar nanoregions (PNRs) in the ergodic state within the shell regions. Comparing the results obtained for two BCZT compositions, it was demonstrated that the stability of the ferroelectric tetragonal phase in slow-cooled BCZT-KBT samples was improved for the ceramic with lower Ca and Zr concentrations, denoted x=0.06, in comparison with that for higher levels, denoted x=0.15. Moreover, the electric field-induced ferroelectric state in the quenched ceramic with x=0.06 was found to be more stable during heating, giving rise to an enhanced depolarisation temperature.

In this thesis, ferroelastic domain switching behaviour of lead zirconate titanate ceramics, as used in devices such as actuators, was studied. In particular, the effect of cyclic frequency and amplitude were assessed to develop a correlation between macrostructural changes and fatigue behaviour, both in the bulk and in crack-tip process zones. A variety of experimental methods were used. Raman scattering enabled the poling state of the ceramics can be determined. However, it could not distinguish between the different preferred orientations of in-plane c-domains. Conversely, neutron and X-ray diffraction technique can detect domain orientation distribution and the preferred direction of c-domains. In this study, neutron diffraction was used to probe domain switching behaviour in bulk samples while high spatial resolution X-rays were employed to analyse a switching zone near a crack tip. Under cyclic mechanical loading, domain switching and the accumulation of ferroelastic strain becomes saturated with increasing number of cycles. Moreover, time-dependent deformation was investigated. The results show that a domain forward-switching process occurs during creep deformation while a domain backward-switching process takes place during recovery. In addition, it was found that the frequency of applied stress affects the saturation of the ferroelastic strain while its magnitude has an influence on the level of strain accumulated. Under static mechanical loading, it was found that the size of the crack-tip zone where stress-induced domain switching occurs with increase in the stress intensity factor but the degree of domain switching around the crack tip changes only slightly. Under cyclic electrical loading, the results present a strong link between the frequency of the applied field, remnant polarisation, domain switching and the resultant crack growth. The results show that polarisation fatigue, the size of the switching zone, and the crack growth rate is greater at lower loading frequency. The quantitative analysis of the time dependent mechanism as well as the effect of loading frequency and amplitude on domain switching was achieved by applying viscoelastic models. Importantly, these models can be used to explain domain switching behaviour and domain wall movement under cyclic loading and link these processes to macroscopic deformation.

Submitted by IDALCI CRUVINEL DOS REIS null (idalcireis@yahoo.com.br) on 2016-01-27T19:12:31Z No. of bitstreams: 1 Tese_Idalci Cruvinel dos Reis.pdf: 11534800 bytes, checksum: bebcb1750beb5d5066bead83c37b196a (MD5) / Approved for entry into archive by Juliano Benedito Ferreira (julianoferreira@reitoria.unesp.br) on 2016-01-28T18:47:45Z (GMT) No. of bitstreams: 1 reis_ic_dr_ilha.pdf: 11534800 bytes, checksum: bebcb1750beb5d5066bead83c37b196a (MD5) / Made available in DSpace on 2016-01-28T18:47:45Z (GMT). No. of bitstreams: 1 reis_ic_dr_ilha.pdf: 11534800 bytes, checksum: bebcb1750beb5d5066bead83c37b196a (MD5) Previous issue date: 2015-12-18 / Fundação de Amparo à Pesquisa do Estado de Goiás (FAPEG) / Neste trabalho, as características estruturais, microestruturais, ferroelétricas e dielétricas de materiais ferroelétricos com estruturas laminares de bismuto (BLSFs), conhecidos como Aurivillius, foram investigadas. Os sistemas objetos de estudo foram compostos bicamadas (SrBi2Nb2O9, SrBi2Ta2O9, BaBi2Nb2O9) e tricamadas (Bi4Ti3O12), onde foi considerada a dopagem do sítio A da estrutura com lantânio (La3+). As propriedades físicas, portanto, foram investigadas considerando a influência do La3+ para várias concentrações. As cerâmicas foram preparadas pelo método de reação de estado sólido com sinterização em temperaturas acima de 1000 °C, para todos os casos. Para o estudo das propriedades estruturais e microestruturais, foram utilizadas as técnicas de difração de raios-x, Espectroscopia Raman, Microscopia Eletrônica de Varredura (MEV) e Espectrometria de Dispersão de Energia (EDS). As propriedades ferroelétricas e dielétricas foram investigadas a partir da dependência da polarização com o campo elétrico e resposta dielétrica com temperatura, respectivamente. Fases puras foram verificadas para todos os sistemas e analisadas com refinamento pelo método de Reitveld. Os resultados apresentaram indícios de alterações nas estruturas das cerâmicas, o que pode ser associado à influência do lantânio na estrutura. Essas alterações foram confirmadas nas medidas de MEV, onde foi possível observar um aumento significativo dos tamanhos médios dos grãos com aumento do dopante para os sistemas bicamadas e uma redução para o sistema tri-camadas. As medidas de Raman identificaram os modos ativos característicos dos sistemas Aurivillius para todos os sistemas estudados, com influência do conteúdo de lantânio na estrutura. As propriedades ferroelétricas foram confirmadas para todos os casos com uma pequena contribuição da condutividade, que pode ser a causa da obtenção de ciclos de histerese aquém da saturação para alguns casos. Em particular, o sistema SrBi2Ta2O9 revelou ciclos bem característicos e definidos, enquanto o sistema BaBi2Nb2O9 mostrou o comportamento esperado para os ferroelétricos relaxores. Picos bem definidos foram observados na resposta dielétrica para todos os casos, observando uma forte influência do conteúdo de dopante nos parâmetros dielétricos. As características da transição de fases revelam comportamentos associados tanto a um ferroelétrico normal quanto ao comportamento típico de relaxores. Este efeito foi discutido detalhadamente para cada caso. É importante destacar que, para todos os casos, baixos valores de perdas dielétricas foram obtidos, muito abaixo dos reportados na literatura para sistemas Aurivillius. Diante destes resultados, os sistemas aqui estudados são fortes candidatos para aplicações tecnológicas. / In this work the structural, microstructural, ferroelectric and dielectric characteristics of ferroelectric materials with bismuth layer structures (BLSFs), known as Aurivillius, were investigated. The studied materials were based on bi-layers (SrBi2Nb2O9, SrBi2Ta2O9, BaBi2Nb2O9) and tri-layer (Bi4Ti3O12) systems, where the lanthanum (La3+) doping in the A-site of the structure has been considered. The physical properties where, therefore, investigated considering the influence of La3+ at various concentrations. The ceramics were prepared by the solid state reaction method for temperatures above 1000 °C for all the cases. For the investigation of the structural and microstructural properties the x-ray diffraction technique, as well as Raman spectroscopy, Scanning Electron Microscopy (SEM) and Energy Dispersive of Spectrometry (EDS) were used. The ferroelectric and dielectric properties were investigated from the electric field dependence of the polarization and dielectric response with temperature, respectively. Pure phases were found for all the systems and analyzed with structural refinement by the Reitveld’s method. The results showed changes in the structure of the ceramics, which can be associated with the influence of the lanthanum content in the structure. These changes were confirmed in the SEM measurements, where a significant increase in average grain size with the increase of the doping content for bi-layer systems, as well as a reduction in average grain size for the tri-layer system, has been observed. The Raman measurements showed the characteristic bands of the Aurivillius systems, with influence of the lanthanum content in the structure, for all the cases. The ferroelectric properties were confirmed in all cases, with a small contribution of the conductivity, which can be the cause for the observation of unsaturated loops in some cases. Particularly, the SrBi2Ta2O9 system showed very well defined hysteresis loops and the BaBi2Nb2O9 system showed the expected behavior for relaxor ferroelectrics. On the other hand, well defined peaks were observed in the dielectric response for all cases, showing a strong influence of the dopant content in the dielectric parameters. The phase transition characteristics revealed behaviors associated with both normal and relaxor ferroelectrics. This effect has been discussed in details for all the cases. Very low values of the dielectric losses were found, when compared to those reported in the literature for typical Aurivillius systems. This result makes the materials studied here promissory systems for practical applications. / FAPEG: 201310267000048

Esse trabalho de dissertação de mestrado teve como principal objetivo obter amostras do sistema Pb1-xLaxTiO3(PLT) com x = 0,10, 0,15 e 0,20 e, a partir desse material, produzir amostras cerâmicas e filmes finos nanoestruturados e caracterizar suas propriedades estruturais e elétricas. As nanopartículas para a produção das cerâmicas e a solução para a deposição de filmes finos foram obtidas através do método dos precursores poliméricos. As amostras cerâmicas foram sinterizadas através do método convencional e do método de prensagem e aquecimento simultâneo. A caracterização estrutural foi realizada através das técnicas de difração de raios X (DRX), espectroscopia Raman e espectroscopia de absorção de raios X. Através das técnicas de DRX e espectroscopia Raman foi possível observar os processos de transição de fase estrutural em função da quantidade de lantânio e do tamanho de partícula. Amostras calcinadas a 400°C, que foram caracterizadas como amorfas, apresentam um espectro de absorção de raios X diferente das demais amostras caracterizadas como cristalinas. As amostras cerâmicas sinterizadas em alta temperatura e a pressão atmosférica apresentaram um comportamento microestrutural (grãos micrométricos) e elétrico (ferroelétrico normal) semelhante ao das amostras preparadas através do método de reação do estado sólido. Por outro lado, a amostra cerâmica com x = 0,20 preparada em alta pressão (7,4 GPa) e a temperatura ambiente apresentou somente grãos nanométricos. A manutenção dos grãos em uma escala nanométrica fez com que essa amostra cerâmica apresentasse um comportamento característico de um material ferroelétrico relaxor ao passo que a mesma amostra preparada através do método de síntese convencional (grãos micrométricos) apresentou um comportamento típico de um material ferroelétrico normal. / The main objective of this work was to obtain ferroelectric materials of Pb1-xLaxTiO3 (PLT) composition, with x = 0.10, 0.15 and 0.20, in nanometer scale in order to prepare nanostructure ceramic and thin films and characterize their structural and electric properties. The nanoparticles used to prepared ceramic samples and the solution used to prepared thin films was obtained using the conventional high temperature sintering method and by using high pressure and high temperature simultaneously. The structural modification due to particle size and lanthanum amount was followed by X-Ray diffraction (XRD), Raman spectroscopy and X-Ray absorption techniques. The transition process was followed from XRD pattern and from the Raman spectra. Samples calcined at 400 oC that were characterized as amorphous present different X-ray absorption spectra. The ceramic samples sinterized at high temperature and ambient pressure presented a microstructure (microsized grains) and electrical properties (normal ferroelectric) similar to that observed in the same samples obtained from the solid-state reaction method. On the other hand, the ceramic sample with x = 0.20 prepared at high pressure and at room temperature formed only by nanoparticles present a behavior characteristic of a relaxor ferroelectric material showing the influence of the grain size on the electrical properties of these samples.

<p>Nano-powders of BaTiO₃, SrTiO₃, Ba_0.6Sr_0.4TiO₃, a mixture of the composition (BaTiO₃)_0.6(SrTiO₃)_0.4 with particle sizes in the range of 60 to 80 nm, and Bi₄Ti₃O₁₂ with an average particle size of 100 nm were consolidated by spark plasma sintering (SPS). The kinetics of reaction, densification and grain growth were studied. An experimental procedure is outlined that allows the determination of a “kinetic window” within which dense nano-sized compacts can be prepared. It is shown that the sintering behaviour of the five powders varies somewhat, but is generally speaking fairly similar. However, the types of grain growth behaviour of these powders are quite different, exemplified by the observation that the kinetic window for the (BaTiO₃)_0.6(SrTiO₃)_0.4 mixture is 125 ^oC, ~75 ^oC for Bi₄Ti₃O₁₂, ~25^oC for BaTiO₃ and SrTiO₃, while it is hard to observe an apparent kinetic window for obtaining nano-sized compacts of Ba_0.6Sr_0.4TiO₃. During the densification of the (BaTiO₃)_0.6(SrTiO₃)_0.4 mixture the reaction 0.6BaTiO₃+0.4SrTiO₃ → Ba_0.6Sr_0.4TiO₃ takes place, and this reaction is suggested to have a self-pinning effect on the grain growth, which in turn explains why this powder has a large kinetic window. Notably, SPS offers a unique opportunity to more preciously investigate and monitor the sintering kinetics of nano-powders, and it allows preparation of ceramics with tailored microstructures.</p><p>The dielectric properties of selected samples of (Ba, Sr)TiO₃ ceramics have been studied. The results are correlated with the microstructural features of these samples, <i>e.g.</i> to the grain sizes present in the compacts. The ceramic with nano-sized microstructure exhibits a diffuse transition in permittivity and reduced dielectric losses in the vicinity of the Curie temperature, whereas the more coarse-grained compacts exhibit normal dielectric properties in the ferroelectric region.</p><p>The morphology evolution, with increasing sintering temperature, of bismuth layer-structured ferroelectric ceramics such as Bi₄Ti₃O₁₂ (BIT) and CaBi₂Nb₂O₉ (CBNO) was investigated. The subsequent isothermal sintering experiments revealed that the nano-sized particles of the BIT precursor powder grew into elongated plate-like grains within a few minutes, via a dynamic ripening mechanism.</p><p>A new processing strategy for obtaining highly textured ceramics is described. It is based on a<i> directional dynamic ripening mechanism</i> <i>induced by superplastic deformation</i>. The new strategy makes it possible to produce a <i>textured</i> microstructure within minutes, and it allows production of textured ferroelectric ceramics with tailored morphology and improved physical properties.</p><p>The ferroelectric, dielectric, and piezoelectric properties of the textured bismuth layer-structured ferroelectric ceramics have been studied, and it was revealed that all textured samples exhibited anisotropic properties and improved performance. The highly textured Bi₄Ti₃O₁₂ ceramic exhibited ferroelectric properties equal to or better than those of corresponding single crystals, and much better than those previously reported for grain-orientated Bi₄Ti₃O₁₂ ceramics. Textured CaBi₂Nb₂O₉ ceramics exhibited a very high Curie temperature, <i>d</i><i>33</i>-values nearly three times larger than those of conventionally sintered materials, and a high thermal depoling temperature indicating that it is a very promising material for high-temperature piezoelectric applications.</p>

Nano-powders of BaTiO3, SrTiO3, Ba0.6Sr0.4TiO3, a mixture of the composition (BaTiO3)0.6(SrTiO3)0.4 with particle sizes in the range of 60 to 80 nm, and Bi4Ti3O12 with an average particle size of 100 nm were consolidated by spark plasma sintering (SPS). The kinetics of reaction, densification and grain growth were studied. An experimental procedure is outlined that allows the determination of a “kinetic window” within which dense nano-sized compacts can be prepared. It is shown that the sintering behaviour of the five powders varies somewhat, but is generally speaking fairly similar. However, the types of grain growth behaviour of these powders are quite different, exemplified by the observation that the kinetic window for the (BaTiO3)0.6(SrTiO3)0.4 mixture is 125 oC, ~75 oC for Bi4Ti3O12, ~25oC for BaTiO3 and SrTiO3, while it is hard to observe an apparent kinetic window for obtaining nano-sized compacts of Ba0.6Sr0.4TiO3. During the densification of the (BaTiO3)0.6(SrTiO3)0.4 mixture the reaction 0.6BaTiO3+0.4SrTiO3 → Ba0.6Sr0.4TiO3 takes place, and this reaction is suggested to have a self-pinning effect on the grain growth, which in turn explains why this powder has a large kinetic window. Notably, SPS offers a unique opportunity to more preciously investigate and monitor the sintering kinetics of nano-powders, and it allows preparation of ceramics with tailored microstructures. The dielectric properties of selected samples of (Ba, Sr)TiO3 ceramics have been studied. The results are correlated with the microstructural features of these samples, e.g. to the grain sizes present in the compacts. The ceramic with nano-sized microstructure exhibits a diffuse transition in permittivity and reduced dielectric losses in the vicinity of the Curie temperature, whereas the more coarse-grained compacts exhibit normal dielectric properties in the ferroelectric region. The morphology evolution, with increasing sintering temperature, of bismuth layer-structured ferroelectric ceramics such as Bi4Ti3O12 (BIT) and CaBi2Nb2O9 (CBNO) was investigated. The subsequent isothermal sintering experiments revealed that the nano-sized particles of the BIT precursor powder grew into elongated plate-like grains within a few minutes, via a dynamic ripening mechanism. A new processing strategy for obtaining highly textured ceramics is described. It is based on a directional dynamic ripening mechanism induced by superplastic deformation. The new strategy makes it possible to produce a textured microstructure within minutes, and it allows production of textured ferroelectric ceramics with tailored morphology and improved physical properties. The ferroelectric, dielectric, and piezoelectric properties of the textured bismuth layer-structured ferroelectric ceramics have been studied, and it was revealed that all textured samples exhibited anisotropic properties and improved performance. The highly textured Bi4Ti3O12 ceramic exhibited ferroelectric properties equal to or better than those of corresponding single crystals, and much better than those previously reported for grain-orientated Bi4Ti3O12 ceramics. Textured CaBi2Nb2O9 ceramics exhibited a very high Curie temperature, d33-values nearly three times larger than those of conventionally sintered materials, and a high thermal depoling temperature indicating that it is a very promising material for high-temperature piezoelectric applications.

Submitted by Aelson Maciera (aelsoncm@terra.com.br) on 2018-02-01T16:29:26Z No. of bitstreams: 1 TeseJAN.pdf: 5398076 bytes, checksum: 23f1bcf63802cdec3d1b5caf6731eca8 (MD5) / Approved for entry into archive by Ronildo Prado (bco.producao.intelectual@gmail.com) on 2018-02-01T19:07:53Z (GMT) No. of bitstreams: 1 TeseJAN.pdf: 5398076 bytes, checksum: 23f1bcf63802cdec3d1b5caf6731eca8 (MD5) / Approved for entry into archive by Ronildo Prado (bco.producao.intelectual@gmail.com) on 2018-02-01T19:08:13Z (GMT) No. of bitstreams: 1 TeseJAN.pdf: 5398076 bytes, checksum: 23f1bcf63802cdec3d1b5caf6731eca8 (MD5) / Made available in DSpace on 2018-02-01T19:11:28Z (GMT). No. of bitstreams: 1 TeseJAN.pdf: 5398076 bytes, checksum: 23f1bcf63802cdec3d1b5caf6731eca8 (MD5) Previous issue date: 2015-08-14 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / We report the investigation of structural, optical and electrical properties of the MgxPb(1- x)TiO3 ceramic system produced by mechanosynthesis. The solid state reaction manufacturing method has been proved to be an efficient alternative to manufacture this type of material. By using Raman spectroscopy techniques it was possible observe the effects induced by pressure, from 0 up to 14 GPa, and by temperature from 10 up to 723 K for the samples with x ranging from 0.2 to 1.0. Complementary characterization techniques were also used, including X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Optical Absorption Spectroscopy and Electrical Impedance. XRD enabled the study of structural changes related to the increase in Mg concentrations. Raman analysis allowed the study of vibrational modes, in particular the transversely optical mode E(1TO) of lower frequency in order to characterize the phase transition from tetragonal-ferroelectric to cubic-paraelectric phases. From these results it was possible to construct a phase diagram that relates Mg concentration, temperature and hydrostatic pressure, yielding determine critical temperature (Tc) and critical pressure (Pc) in which phase transition occurs for each sample. Permittivity dielectric measurements were performed for each material, through which it was possible to compare the effects of Mg ratios in the modification of the values of these properties. Finally, a study of optical absorption as a function of Mg concentration was conducted, evidencing changes in gap energies related to the increase of Mg incorporation. The lowest values, 2.86 and 2.9 eV correspond to samples with concentrations of 0.4 and 0.2, respectively. Thus, from a technological point of view, these characteristics are interesting for applications in devices operating in the microwave region. / Neste trabalho foram investigados os efeitos estruturais, ópticos e elétricos do sistema cerâmico MgxPb(1-x)TiO3 produzido por mecano-síntese. O método de fabricação de reação de estado sólido mostrou-se uma alternativa eficiente de fabricação do material. Utilizandose de técnicas de espectroscopia Raman, foram observados os efeitos da pressão, de 0 a 14 GPa, e temperatura, de 10 a 723 K, para as amostras com x variando de 0,2 a 1,0. Também foram usadas técnicas complementares de caracterização entre elas a Difração de Raio-X (DRX), Microscopia Eletrônica de Varredura (MEV), Absorção Óptica e de Espectroscopia de Impedância Elétrica. A técnica de DRX possibilitou o estudo da alteração estrutural relacionada ao aumento das concentrações de Mg. As análises Raman permitiram o estudo dos modos vibracionais, em especial o modo transversal óptico E(1TO) de mais baixa frequência, a fim de caracterizar a transição de fase, da fase tetragonal ferroelétrica para a cúbica paraelétrica. A partir desses resultados foi possível construir um diagrama de fase relativo à concentração de Mg, com a temperatura e pressão hidrostática, obtendo-se temperatura crítica (Tc) e pressão crítica (Pc) nas quais ocorrem transição de fase para cada amostra. Foram realizadas medidas de permissividades dielétricas para cada material, por meio das quais foi possível a comparação dos efeitos das proporções Mg na alteração dos valores dessas propriedades. Por fim, foi realizado um estudo de absorção óptica em função da concentração de Mg, onde mostrou-se que há alteração do gap relacionada ao aumento da concentração de Mg. Os valores mais baixos, 2,86 e 2,9 eV correspondem a amostras com concentração de 0,4 e 0,2, respectivamente. Assim, do ponto de vista tecnológico, as características encontradas mostram-se úteis para dispositivos que operam na região das micro-ondas.

Esse trabalho de dissertação de mestrado teve como principal objetivo obter amostras do sistema Pb1-xLaxTiO3(PLT) com x = 0,10, 0,15 e 0,20 e, a partir desse material, produzir amostras cerâmicas e filmes finos nanoestruturados e caracterizar suas propriedades estruturais e elétricas. As nanopartículas para a produção das cerâmicas e a solução para a deposição de filmes finos foram obtidas através do método dos precursores poliméricos. As amostras cerâmicas foram sinterizadas através do método convencional e do método de prensagem e aquecimento simultâneo. A caracterização estrutural foi realizada através das técnicas de difração de raios X (DRX), espectroscopia Raman e espectroscopia de absorção de raios X. Através das técnicas de DRX e espectroscopia Raman foi possível observar os processos de transição de fase estrutural em função da quantidade de lantânio e do tamanho de partícula. Amostras calcinadas a 400°C, que foram caracterizadas como amorfas, apresentam um espectro de absorção de raios X diferente das demais amostras caracterizadas como cristalinas. As amostras cerâmicas sinterizadas em alta temperatura e a pressão atmosférica apresentaram um comportamento microestrutural (grãos micrométricos) e elétrico (ferroelétrico normal) semelhante ao das amostras preparadas através do método de reação do estado sólido. Por outro lado, a amostra cerâmica com x = 0,20 preparada em alta pressão (7,4 GPa) e a temperatura ambiente apresentou somente grãos nanométricos. A manutenção dos grãos em uma escala nanométrica fez com que essa amostra cerâmica apresentasse um comportamento característico de um material ferroelétrico relaxor ao passo que a mesma amostra preparada através do método de síntese convencional (grãos micrométricos) apresentou um comportamento típico de um material ferroelétrico normal. / The main objective of this work was to obtain ferroelectric materials of Pb1-xLaxTiO3 (PLT) composition, with x = 0.10, 0.15 and 0.20, in nanometer scale in order to prepare nanostructure ceramic and thin films and characterize their structural and electric properties. The nanoparticles used to prepared ceramic samples and the solution used to prepared thin films was obtained using the conventional high temperature sintering method and by using high pressure and high temperature simultaneously. The structural modification due to particle size and lanthanum amount was followed by X-Ray diffraction (XRD), Raman spectroscopy and X-Ray absorption techniques. The transition process was followed from XRD pattern and from the Raman spectra. Samples calcined at 400 oC that were characterized as amorphous present different X-ray absorption spectra. The ceramic samples sinterized at high temperature and ambient pressure presented a microstructure (microsized grains) and electrical properties (normal ferroelectric) similar to that observed in the same samples obtained from the solid-state reaction method. On the other hand, the ceramic sample with x = 0.20 prepared at high pressure and at room temperature formed only by nanoparticles present a behavior characteristic of a relaxor ferroelectric material showing the influence of the grain size on the electrical properties of these samples.

No description available.