Academic literature on the topic 'Calcium Titanate Ceramics'

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior<br>Barium titanate (BaTiO3 - BT) is a ferroelectric material with important technological applications. When partially doped with trivalent cations at the barium sublattice or pentavalent at the titanium sublattice, BaTiO3-based ceramics exhibit a semiconductive character, accompanied by a Positive Temperature Coefficient of Resistivity (PTCR). Several ways of BT modifications have been proposed in literature, as example, the use of different synthesis methods and the doping with different ions. Therefore, in the present work we have as objective the synthesis, sintering and electrical characterization of the rare earth ions (RE = La3+, Y3+, Er3+, Nd3+ e Eu3+) doped barium calcium titanate ceramics (Ba0,77Ca0,227RE0,003TiO3 BCT_RE) in order to study mainly the PTCR behavior. The powder synthesis was done by the polymeric precursor method followed by the sinterization at reducing atmosphere during the heating up ramp and different atmosphere during cooling down ramp in order to investigate the atmosphere and dopant effect on PTCR behavior. The characterization was done using the Differential Thermal Analysis, Thermogravimetry, Scanning Differential Calorimetry, X-ray Powder Diffraction, Scanning Electron Microscopy and Impedance Spectroscopy techniques. The calcined powder at 600ºC/4h presented majority BCT phase and after sintering at 1350ºC/6h, a small amount of Ba6Ti17O40 phase was observed. The sintered ceramics presented a homogeneous grain size distribution but with the presence of a secondary phase at the grain boundary for all compositions, and Curie temperature at about 120ºC. The PTCR characteristics of the ceramics were studied as a function of the sintering atmosphere and dopant type. In summary, all the samples, exception of the Eu doped samples, presented PTCR behavior in all the studied conditions. .<br>O titanato de bário (BaTiO3 - BT) é um material ferroelétrico com importantes aplicações tecnológicas. Quando dopado com íons trivalentes no sítio do bário ou pentavalentes no sítio do titânio, cerâmicas de BaTiO3 exibem um caráter semicondutor, acompanhado por um coeficiente positivo da resistência com o aumento da temperatura (PTCR). Diversas formas de modificação do BT têm sido sugeridas na literatura, por exemplo, a utilização de diferentes métodos de síntese e a dopagem com diferentes íons. Dessa forma, no presente trabalho tivemos como objetivo a síntese, a sinterização e a caracterização elétrica de cerâmicas de titanato de bário e cálcio (Ba0,77Ca0,227RE0,003TiO3 BCT_RE) dopados com íons terras raras (RE = La3+, Y3+, Er3+, Nd3+ e Eu3+), visando principalmente o estudo do comportamento PTCR. A síntese dos pós foi realizada pelo método dos precursores poliméricos, seguido pela sinterização em atmosfera redutora durante o aquecimento e diferentes atmosferas no resfriamento com o intuito de investigar a influência da atmosfera e do dopante no comportamento PTCR. A caracterização foi feita utilizando as técnicas de Análise Térmica Diferencial, Termogravimetria, Calorimetria Exploratória Diferencial, Difração de Raios X, Microscopia Eletrônica de Varredura e Espectroscopia de Impedância. Os pós calcinados a 600ºC/4h apresentaram fase majoritária BCT e após sinterizados a 1350ºC/6h foi observada a presença da fase Ba6Ti17O40. As cerâmicas sinterizadas apresentaram uma distribuição homogênea de tamanho de grão, porém com a presença de uma segunda fase na região de contorno de grão para todas as composições, com temperatura de Curie em torno de 120ºC. As características PTCR das cerâmicas foram estudadas em função da atmosfera de sinterização e do tipo do dopante. Em resumo, todas as amostras, com exceção das dopadas com Eu, apresentaram comportamento PTCR para todas as condições estudadas.

Made available in DSpace on 2014-06-11T19:32:11Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-08-15Bitstream added on 2014-06-13T18:43:10Z : No. of bitstreams: 1 jesus_mm_dr_araiq.pdf: 3120238 bytes, checksum: 8758936a6c6913fe23da8e0dd94e4296 (MD5)<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)<br>Titanato de cálcio possui estrutura tipo perovisquita com interessantes propriedades elétricas para aplicações tecnológicas, como termistores, capacitores multicamadas e memória DRAM. Para a indústria cerâmica e eletrônica, pesquisas com perovisquita tem aumentado sua importância devido a propriedade fotoluminescente observada nesses materiais. Neste trabalho, o titanato de cálcio puro e dopado com escândio nas concentrações 0,25;0,5 e 1,0% mol foi sintetizada pelo método dos precursores poliméricos. Este método é baseado na quelação dos cátions por ácido cítrico em etileno glicol. Os pós foram calcinados variando a temperatura de 350º a 850°C. Os resultados da análise térmica mostraram que a obtenção de pós amorfos com baixo teor de matéria orgânica está diretamente relacionado à ordem estrutural da estrutura perovisquita. Os pós amorfos e cristalinos puro e dopado com Sc foram caracterizados por termogravimétria e pela técnica da calorimetria exploratória diferencial (TG/DSC), espectroscopia de infra vermelho (IR), Raman, espectroscopia UV-visível, microscopia eletrônica de transmissão (TEM), fotoluminescência e difração de raio X, onde foi usado refinamento pelo Método de Rietveld. A adição de Sc causou um decréscimo da cela unitária e causou interferência na distribuição dos cátions nos sítios octaédricos formando vacâncias de cálcio e conseqüentemente aumentando a desordem. Medidas de fotoluminescência desses materiais mostraram uma intensa banda larga atribuída à desordem do CT e CTSc.<br>Calcium titanate presents perovskite type structure with interesting electrical properties for technological applications, such as thermisters, multilayer capacitors and DRAM memories. For the ceramic and electronic industries, research with perovskite has increased in importance due to the photoluminescent properties observed in these materials. In this work pure and Sc doped CaTiO3 at concentrations of 0.25, 0.5 and 1% molar was synthesized through the method of polymeric precursors . This method is based on the chelation of cations through citric acid in ethylene glycol solvent. The materials were calcined at temperatures varying from 350 to 850°C. The experimental results obtained through thermal analysis showed that the condition to obtaining amorphous powder with low content of organic matter is directly related to structural order of perovskite structure. The crystalline and amorphous pure and Sc doped powder was characterized through termogravimetric and diferential scaning calorimetry technique (TG/DSC), infrared spectroscopy (IR), Raman, UVvisible spectroscopy, transmission electron microscopy (TEM), photoluminescence and x-ray diffraction were used, refinement through method of Rietveld. Addition of Sc caused a decrease in the unitary cell and caused interference in the distribution of the cations in octahedral sites forming calcium vacancies, and consequently increasing the disorder. The Photoluminescent s of these materials showed an intense large band, attributed to the disorder of CT e CTSc.

Made available in DSpace on 2014-10-09T12:34:02Z (GMT). No. of bitstreams: 0<br>Made available in DSpace on 2014-10-09T13:59:37Z (GMT). No. of bitstreams: 0<br>Tese (Doutoramento)<br>IPEN/T<br>Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Polymer and composite polymer-ceramic nanofibers were prepared by electrospinning process. Solution of 20 wt.% polyvinylidene fluoride (PVDF) in a mixture of dimethyl sulfoxide (DMSO) and acetone in the ratio of 7:3 was chosen as the most suitable precursor. When preparing composite nanofibers, 20 wt.% of barium calcium zirconate titanate (BCZT) or barium titanate (BT) nanoparticles was added to this PVDF solution. Given parameters were defined as the most suitable for the process of electrospinning: voltage of 50 kV, feeding rate of 30 l/min, distance between emitter and collector of 20 cm and needle diameter of 17 G. The effect of polymer molecular weight and the rotation speed of collector was also studied. Various properties of prepared samples were studied: morphology and fiber diameter, phase composition with the use of x-ray diffraction and Fourier transform infrared spectroscopy and also chosen electrical properties. Lower fiber diameters appeared with lower polymer molecular weight and higher rotation speed of the collector. These parameters resulted in higher percentage of the piezoelectric phase as well. The smallest achieved fiber diameter was around 300 nm, the highest percentage of phase was 92 % and the highest piezoelectric constant had a value of 16 pC/N. Composite fibers filled with BT particles showed better properties that the ones filled with BCZT particles.

碩士<br>國立臺灣科技大學<br>機械工程系<br>89<br>Abstract In addition to the highly anisotropic piezoelectric properties, calcium modified lead titanate ceramics have unique microstructural characteristics — extra reflections in diffraction patterns. In this thesis, we studied the microstructures and ferroelectric fatigue behavior of calcium modified lead titanate ceramics (Pb1-xCaxTiO3, PCT) by investigating the microstructural characteristics. The PCT samples (x＝0.5, PCT55) were prepared employing an oxide-mixing method and sintered at 1200℃ for 0.5 to 20 hrs. In order to investigate the relationship between microstructure and ferroelectric fatigue characteristics, we analyzed the crystal structure of PCT using X-ray diffractometry, examed the ordering behavior and microstructures by transmission electron microscopy (TEM) and measured the ferroelectric hysteresis curves with a standard ferroelectric tester Precision Workstation. Results of X-ray diffraction patterns showed that PCT55 is pseudocubic crystal structure. But patterns still exhibited no superlattice peaks even if the sintering time prolonged. TEM investigations showed that the electron diffraction patterns of PCT55 sintered for 2 and 20 hrs showing extra reflections of 1/2{100}, 1/2{110} and 1/2{111}. No obvious domain arrangement could be observed in the bright field images of PCT55 sintered for 20 hrs, while the dark field images using super-reflections showed two distinct planar defects: an anti-phase boundary due to an ordering structure and the other complex fringe that is attributed to oxygen octahedral tilting. According to the dark field images from different reflections and the simulation of octahedral tilting, we infer that the 1/2{100}, 1/2{110} and 1/2{111} reflections might be derived from octahedral tilting. However, in addition to octahedral tilting, the atomic ordering contributes to the 1/2{111} reflections. For the as-sintered PCT55 for 20 hrs specimens, the ferroelectric fatigue properties results showed that the remanent polarization (Pr) was 5μC/cm2, while the coercive field (Ec) was 5.0 kV/cm. After switching up to 2×106 cycles, the ferroelectric hysteresis curves showed an increasing trend in Pr and a decreasing tendency in Ec, 6μC/cm2 and 4.7 kV/cm, respectively. In the fatigue microstructural evolution, most of the specimens exhibited no domain structure or plain domain arrangements as before the fatigue test, but the intensities of the superlattice reflections and the fringe contrast of dark field images became weaker. The unique ferroelectric fatigue behavior of PCT55 might be resulted from the change of microstructures. In summary, the atomic ordering and oxygen octahedral tilting structures contribute to the extra reflections in electron diffraction patterns and two distinct fringes in dark field images and result in the unique fatigue behavior of PCT55. After repeated electrical switching, these microstructural reactions play important roles and influence the fatigue behavior significantly.

碩士<br>國立臺灣科技大學<br>工程技術研究所材料科技學程<br>88<br>The Pb1-xCaxTiO3（PCT）ceramics show many excellent properties such as ferroelectricity、piezoelectricity and pyroelectricity, and an A-site ordering type was reported inside the microstructure of the perovskite. However controversial arguments in this topic were recently presented. In this thesis we studied the mocrostructural characteristics and ferroeletric properties of PCT using electron microscopy and electron diffraction primarily. The PCT ceramic samples were prepared employing an oxide-mixing method, with different Ca-content （x＝0.3、0.4、0.5） sintered at 1200℃~1250℃ for 0.5~20 hrs; In order to understand domain switching of materials under electrical field application, and influence of microstructure on P-E curves, we analyzed the crystal structure of PCT using X-ray diffractometer; to observe the surface and internal microstructure of PCT, scanning electron mocroscope（SEM） and transmission electron mocroscope（TEM） were employed; to discuss the ordering structure between atoms, high resolution transmission electron mocroscope（HRTEM） and laser optical diffraction studies were carried out; to analysis the phase change and thermal expansion, a thermal mechanic analysis（TMA）was utilized; to measure polarization－field （P－E）curves of PCT ceramics, a Sawyer-Tower curcit was used. X-ray diffraction results show that increasing of Ca content makes c/a ratio of PCT approach to 1, and the crystal structure changes from tetragonal to pseudocubic. The amount of Ca decreases c/a ratio increases. Grain sizes of specimens increase as the sintering time prolonged, and composition homogeneity of materials could be improved at the same time. TEM investigations show that 90°domain structures were induced due to internal strain formation,when the specimens were cooled from high temperatures. In electron diffraction patterns, 1/2{100}、1/2{110}、1/2{111} extra reflections were found in Pb0.5Ca0.5TiO3（PCT55）, but were not observed in PCT73. Using HRTEM and laser optical diffraction, calcium-containing specimens (X=0.4, X=0.5) partial-order structures existing in were demonstrated; 1/2{100} and 1/2{111} ordering structures could be observed in atomic images of PCT55 and laser optical diffraction for zone axes of [001] and [1 0]. We also found that atoms in some area would shift along <110> directions, without ordering characteristics and the 1/2{110} extra reflections could be observed in optical diffraction patterns. An tilted octahedron model was proposed and the existing of three extra reflections at 1/2{100}、1/2{110} and 1/2{111}were demonstrated by computer simulation. From the present results, we realize that among three extra reflections 1/2{100} and 1/2{111} appear to be attributed to both lattices ordering and TiO6 octahedron tilting, and 1/2{110} was probably caused by tilted octahedrons in the material. Ferroelectric properties and microstructural characteristics correlating suggest that ferroelectric domain boundary pinning constrains the remanent polarization in PCT ceramics with lower Ca-content. Ordering and octahedron tilting may contribute to material hardness as well as some other electrical properties.

碩士<br>國立成功大學<br>資源工程學系<br>106<br>In this study, calcium-doped barium titanate (BCT) powders were used as the raw materials to study different amounts of acceptor doping effects on the microstructure, crystal structure, and electrical properties of BCT. The A/B ratio of (Ba0.92Ca0.08)Ti1.005O3 was set for Ti-excess to prevent Ca doping onto the B-site. Powder of (Ba0.92Ca0.08)Ti1.005O3 was calcined at 1100°C which temperature can make the powder no second phase. Based on the Rietveld analysis results, Ca in the BCT mainly entered A-site to replace Ba. To simulating the MLCC sintering condition, the BCT ceramics should be sintered in reduction atmosphere to prevent the Ni electrode oxidation, and we also add different amounts of MnCO3 as acceptor to prevent the ceramic samples from semiconduction. The grain sizes after sintering are approximately 0.36 μm which fits the MLCC condition. In this study, We use two RQ equivalent circuit model to fit the impedance spectroscopy data, and the results meet the Curie-Weiss behavior. According to the impedance spectroscopy data, the grain and grain boundary conductivity of acceptor-doped BCT ceramics is determined by Vo ̈ and e' respectively. With the increase of the amount of addition, the grain and the grain boundary conductivity tends to increase. The similar grain and grain boundary conductivity of BCT ceramics are due to maintain the electric neutrality. While the depletion layer and grain boundary barrier height are tend to decrease as the amounts of acceptor increase. The comprehensive conclusions show that the amounts of acceptor (MnCO3) has a certain influence on the electrical analysis calculated by the impedance spectroscopy analysis.

博士<br>國立成功大學<br>化學工程研究所<br>84<br>Titanium alkoxide in strong alkaline condition can react with strontium ion to become strontium titanate without any external heat. Because titanium alkoxide is easy to react with the mois- ture in the air to form hydrolyzed gel of titanium dioxide to affect the quality of the product. Titanyl acylate precursor from chelating acetic acid with titanium alkoxide can be dissolved in water and be reacted with strontium ion to form strontium titan- ate powder in strong alkaline solution. In the studies that the preparatory conditions of titanyl acylate precursor reacting with strontium ion to form strontium titanate powder in a strong alkaline solution conditions, reac- tion temperature, the water content of forming titanyl acylate precursor, the ratio of water/titanium alkoxide and the ratio of acetic acid/titanium alkoxide, have been studied the effect on the particle size, stoichometry and sinterability of making cer- amic powder. The preparatory variables affect indirectly the amount of chelating acetate group, change the mode of condensa- tion of the gels and even control the particle size of the powder . The reaction rate of forming powder, at lower temperature (room temperature) and less water content (water/ titanium alkoxide = 5) or fewer acetic acid (acetic acid/ titanium alkoxide =5), is slow and the particle size of the powder is bigger. That the sinter- ability of powder is no so good. On the contrary, that of form- ing powder, at higher temperature such as 373 K and more water content (the ratio of water to titanium alkoxide is 20) or larger acetic acid (the ratio of acetic acid to titanium alkoxide is 10) , is rapid and the particle size formed is finer at 0.1um.(omit)