Dislocation loops in pressureless-sintered undoped BaTiO3 ceramics have been analysed via transmission electron microscopy (TEM). The Burgers vector b = [100] of the loops was initially determined by the contrast analysis of the g•b = 0 criteria combining with the inside-outside contrast method by which the sense of the Burgers vector was concluded. The vacancy nature were determined by adopting the inside-outside contrast analysis using the criteria of (g•b)sg being positive or negative when the loops were imaged under kinematical diffraction conditions of sg ¡Ú 0. High-resolution imaging of such loops has enabled us to confirm its vacancy nature, consistent with the contrast analysis. Further, the loops¡¦ Burgers vector was determined to be b = 1/2[100] and the loops were therefore negative partial dislocation loops lying in {200} where part of the TiO2-deficiency existed locally in the grains of sintered BaTiO3 ceramics was accommodated by the presence of vacancy loops. It is suggested that the extrinsic defects of both titanium and oxygen vacancies ( and ,) generated by the non-stoichiometry which gave clustered during sintering in air are responsible for the formation of the dislocation loops.

Thesis (Ph. D.)Oregon Graduate Center, 1986.

Thesis (Ph. D.)--Oregon Graduate Center, 1988.

The theory of ferroelectricity, and in particular the ferroelectric behavior of barium titanate, are discussed and qualitative agreement is obtained with experimental results. Limitations of the theory are pointed out. Experimental procedure used to manufacture samples of polycrystaline barium titanate ceramic, and to investigate their ferroelectric properties is outlined. The phenomena of permanent polarization and hysteresis are investigated in the ferroelectric temperature range, and are discussed. An electric equivalent of the Barkhausen effect is observed. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Ph.D. / Materials Science and Engineering / Polytitanates in the BaO- TiO2 system with Ba:Ti ratios ranging from 1:2 to 1:5 were prepared using a low temperature technique developed by Pechini. The samples were heated at 600 to 1300°C in oxygen. Room temperature Raman spectroscopy was used to investigate the phase relations in this system. Results of this study indicate the following: except for BaTi4O9, the powders of these compounds were amorphous when heated at 600°C for 4hrs; the compound BaTi2O5 is a low temperature stable phase; Ba6Ti17O40 forms only at temperatures above 1100°C; Ba4Ti13O30 does not form below 1000°C; the single phase BaTi4O9 structure was observed at 1200°C'; the Ba2Ti9O20 phase is obtained only after long heat treatment at 1200°; BaTi5O11 was stable up to 1200°C, at which it decomposes into Ba2Ti4O20 and TiO2. After determination of stability relationships in this system, the electrical conductivities of these compounds were examined as a function of temperature and oxygen partial pressure. For all the temperatures (850-1150°C) studied, the conductivities of these compounds increased with decreasing oxygen partial pressure resulting in n-type properties throughout the whole P[subscript O2] range (10[superscript -19 - 1atm). The P[subscript O2] dependencies of the electrical conductivity were found to be linear for an extensive range of oxygen partial pressures. On the basis of structural considerations the conductivity data was described by a majority defect model consisting of both singly and doubly ionized oxygen vacancies. For lower oxygen partial pressure values a drastic change in the electrical conductivity was observed. This is believed to result from increasing defect interaction for larger departures from stoichiometry. A defect model based on this interaction is proposed to account for the observed sharp change in the electrical conductivity values.

Secondary abnormal grain growth (SAGG) during sintering of barium titanate has been explained in terms of twin plane re-entrant edge (TPRE) growth mechanism by {111} double twin lamellae. But during sintering of Ti-excess barium titanate, {111} double twins lamellae are observed with out SAGG. In our group, Lin founded that when combine two different Ba/Ti ratio of powder to sintering above the eutectic temperature, the SAGG is observed in the interface between two different powders. Therefore, this thesis consists of three major researches: (a) {111} double twin, (b) Ba/Ti ratio, (c) liquid phase. In the experiment, we follow Lin¡¦s experiment to sinter the specimen contain with SAGG. And in this specimen, it can observe the specimen divided into three type of growth grain: (a) top surface with normal grain growth (NGG), (b) intermediate layer with abnormal grain growth (AGG), (c) bottom layer with secondary abnormal grain growth. It can all observed {111} double twin in these three different type of layer. This result confirmed that SAGG are not induced by TPRE growth mechanism. Then we used SEM/EDS to analysis the Ba/Ti ratio in the different type of grain growth layer. The Ba/Ti ratio in this analysis is not differing in NGG, AGG and SAGG. Therefore, we used OM, SEM, TEM to observe the grain boundary and triple grain junction in NGG, AGG and SAGG. It can observe that only the grain boundary and triple grain junction in SAGG are complete wetting. The experimental results shows that the grain growth behavior controlled by the liquid phase wetting degree.

Master of Science / Department of Electrical and Computer Engineering / Andrew Rys / Since its discovery in the 1940's, barium titanate has become one of the more popular dielectric materials for use in discrete capacitors due to its high relative permittivity. Recently, consumer electronics have decreased in size, driving the need for smaller electronic components. To fill this need, researchers have created polycrystalline barium titanate with individual grains in the nanometer scale. With this decrease in size, many problems arise. This paper will outline the effects on the dielectric properties due to shrinking the individual grains, as well as discuss techniques for dielectric measurement of this material.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Includes bibliographical references. / by Mark V. Parish. / M.S.

Compósitos cerâmicos planares de titanato zirconato de bário, BaTi1-xZrxO3, foram produzidos e os efeitos da quantidade de Zr4+ em suas propriedades funcionais foram estudados. As amostras foram fabricadas pelo método convencional de processamento cerâmico e pela técnica de deposição de fitas cerâmicas a partir de BaTi1-xZrxO3 com x=0, 0,05, 0,1, 0,15 e 0,2 sintetizados pelo método hidrotermal e pelo método dos precursores poliméricos. Foram realizadas caracterizações estrutural (difração de Raios X pelo método do pó e espectroscopia Raman), composicional (espectroscopia por dispersão de energia), microestrutural (microscopia eletrônica de varredura, ensaios de dilatometria) e funcional (permissividade elétrica, coeficiente piezoelétrico d33, coeficiente piroelétrico e histerese ferroelétrica). Além disso, a regra da mistura de fase foi utilizada para prever a permissividade elétrica dos compósitos e as tensões mecânicas internas e seus efeitos na permissividade elétrica e na temperatura de Curie de policristais de BaTiO3 foram simulados. As análises dos dados e as discussões foram realizadas considerando o modelo fenomenológico de Devonshire, a modificação de Forsbergh deste modelo para incluir efeitos de tensões mecânicas bidimensionais e o modelo de policristal tetragonal de BaTiO3 sugerido por Buessem. Os resultados mostram a existência de tensões residuais bidimensionais que surgem após o resfriamento dos compósitos devido às diferenças nos coeficientes de expansão térmica das fases constituintes. Os métodos de obtenção das amostras afetaram o tamanho final dos grãos e as espessuras das interfaces dos compósitos, sendo que, em geral, eles são menores e mais finos nas fitas cerâmicas homogêneas do que nas correspondentes cerâmicas homogêneas. Os compósitos apresentaram deslocamento da Tc para maiores temperaturas e aumento do grau de difusividade da transição. A presença das tensões mecânicas residuais e as características microestruturais, juntamente com os modelos utilizados, explicam qualitativamente a permissividade elétrica obtida. Concluí-se que a quantidade de Zr4+ modifica o comportamento das camadas durante a sinterização e altera o coeficiente de dilatação. Estas mudanças geram tensões mecânicas residuais que afetam a microestrutura e as propriedades funcionais dos compósitos. Portanto, a produção de compósitos cerâmicos ferroelétricos deve considerar a correlação existente entre microestrutura e tensões residuais para que suas propriedades sejam otimizadas. / Planar BaTi1-xZrxO3 ceramic composites had their functional properties investigated. These composites were obtained by the conventional ceramic processing technique and by tape casting technique. Furthermore, BaTi1-xZrxO3 x=0, 0.05, 0.1, 0.15 and 0.2 were synthesized by the polymeric precursors method and by the hydrothermal synthesis to study the synthesis influences and to study the effect of Zr4+ on the functional properties of the composites. Structural characterization (X-Ray powder diffraction and Raman spectroscopy), compositional analysis (energy dispersive X-Ray spectroscopy), microestrutural evaluation (scanning electron microscopy, dilatometry measurements) and functional properties characterization (electrical permittivity, piezoelectric coefficient d33, pyroelectric coefficient and ferroelectric hysteresis) were performed. Furthermore, the composites electrical permittivity was predicted by the simple mixture and the internal mechanical stress distribution and it´s effects on both, electrical permittivity and Curie´s temperature (Tc) of BaTiO3 polycrystals, were simulated. The analyses and discussions were supported by 1- Devonshire´s phenomenological theory, 2- Forsbergh´s modification to Devonshire´s theory to include the two-dimensional stress effects on Tc and 3- Buessem´s BaTiO3 tetragonal polycrystal model. The results show that the sintered composites present two-dimensional residual stresses after cooling due to the constrained sintering of the layers and their thermal expansion coefficient mismatch. The methods of sample preparation led to differences in grain size and interface thickness, with the homogeneous ceramic tapes presenting smaller grain sizes and thinner thickness than the conventional homogeneous ceramics. On the other hand, the composites showed a Tc shift to higher temperatures, a more diffuse phase transition and residual mechanical stresses. Concluding, the Zr4+ substitution of Ti4+ modifies the layer´s sintering behavior and their thermal expansion coefficient. These changes lead to microstructure modifications that affect the functional properties of planar BaTi1-xZrxO3 composites. Thus, the design of ferroelectric composites should take into consideration the correlations between microstructure and residual stresses in order to optimize their functional properties.

Thesis (M.S.)--University of Wisconsin--Madison, 1965. / eContent provider-neutral record in process. Description based on print version record. Bibliography: l. 48.