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In this work, we investigate electric field effect (>3 kV.cm-1) on perovskite compound, CaTiO3 (ferroelastic) and BaTiO3 (ferroelectric). This electric field acts like an external force in selection, orientation and distribution of piezoelectric/ferroelastic domains. The electric field can act on nucleation, the partition coefficient of species and the possible modification phases diagrams of a material during its growth. Indeed ions within an electric field see their energy changing which implies a new thermodynamic equilibrium.In the first part, we discuss about crystal growth of CaTiO3 with different growth parameters (velocity of cristal growth vG, electric potential V). By varying this parameters, we can control crystal shape and can alter the crystalline orientation of domains. Same results are found with BaTiO3.In a second step, we used Mirror Electron Micrsocopy (MEM) and Low Energy Electron Microscopy (LEEM) to caracterize domains walls at the surface of calcium titanate. Polarity of domains walls have been prooved recently, and so we have investigated surface potential between samples grown under or without electric field.; Durant ce travail de thèse, nous avons étudié l’effet d’un champ électrique intense (>3 kV.cm-1) sur des matériaux à structures pérovskites, le ferroélastique CaTiO3 et le ferroélectrique BaTiO3. Un tel champ agit comme une force extérieure dans la sélection, l’orientation et la distribution des domaines. Son application durant la croissance modifie la nucléation, le coefficient de partage des espèces et la possible modification du diagramme de phase du matériau considéré. En effet les ions dans un champ électrique voient leur énergie changer ce qui implique un nouvel équilibre thermodynamique. La première partie est dédiée à la croissance cristalline de CaTiO3 lorsque plusieurs paramètres de croissance sont modifiés (vitesse de croissance vG et potentiel électrique V). En faisant varier ces paramètres, nous montrons que nous pouvons contrôler la morphologie du cristal et ainsi altérer l’orientation cristalline desdomaines. Des résultats similaires sont retrouvés avec BaTiO3.Plusieurs techniques expérimentales ont été employées dans le but d’étudier la microstructure des composés notamment la microscopie électronique miroir (MEM) et la microscopie électronique à faible énergie (LEEM) afin de caractériser les domaines et parois de domaines à la surface du titanate de calcium. La polarité de ces parois ayant été récemment prouvée, nous avons étudié et comparé le potentiel de surface entre les échantillons qui ont été élaborés sous et sans champ électrique.

Asymmetric dense and thin membranes have been prepared from powders of perovskite oxide-type CaTiO3 without cracking by phase inversion method. Polyetherimide was used as a polymeric binder in the method. The resulting green membranes, composed of CaTiO3 powder and polyetherimide binder, were sintered at 890, 1100 or 1200 °C. The crystal phase of CaTiO3 was analyzed using X-Ray Diffraction (XRD). The XRD pattern of the synthesized CaTiO3 powder was matched with the reference indicating the formation of CaTiO3 structure. Sintering at 890 °C fails to form a strong membrane. Scanning Electron Microscope (SEM) images of the membranes showed that the membrane had the asymmetric structure with dense layer on one side and porous layer on the other side. The pores in the porous layer were both finger-like and sponge-like structure. The mechanical strength of the membranes, which were determined by Vickers micro hardness method, varied from 3.5 to 25.8 Hv. The strongest membrane without any crack was resulted from sintering at 1200°C with hardness values between 19.4 and 25.8 Hv. Thermal expansion coefficients of the asymmetric membranes sintered at 1100 and 1200 °C, measured with Thermomechanical Analyzer (TMA), were 10.82 × 10-6 and 12.78 × 10-6.C-1 respectively.

Made available in DSpace on 2018-12-11T17:33:04Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-06-01 The traditional methods to synthesize nanocrystalline materials are energy-intensive and time-consuming. This paper describes a fast and simple route to synthesize CaTiO3, which requires just 30 s of processing in the HTMW system to produce the crystalline orthorhombic phase of CT with a micro-cube-like structure. The product's crystallinity increases along with synthesis time. A correlation is identified between microwave processing time and structural crystallinity. Department of Chemistry UFG Campus Catalão Department of Mathematics UFG Campus Catalão Institute of Physics UFG Campus Goiânia Department of Chemistry Univ. Estadual Paulista UNESP INCTMN Institute of Chemistry UNESP Department of Chemistry Univ. Estadual Paulista UNESP INCTMN Institute of Chemistry UNESP

Calcium titanate (CaTiO3) ceramics with perovskite structure were produced by solid state reaction. Calcium carbonate (CaCO3) and titanium dioxide (TiO2) were mixed (in molar ratios 1/1 and 3/2), and the obtained mixtures were calcined at 1150 ?C in successive thermal cycles. The obtained samples were characterized by differential thermal analysis, thermogravimetry, X-ray diffraction, measurement of particle size distribution and linear thermal shrinkage. XRD results indicated that the samples have perovskite CaTiO3 structure with small amount of secondary CaO and TiO2 phases, and their phase composition depends on the heat treatment conditions. The measured values of electrical resistivity were within the characteristic range of insulating materials and approach values corresponding to semiconducting ceramics.

The vacancy ordering behavior of an A-site deficient perovskite system, Ca1-xLa2x/3TiO3, was studied using atomic resolution scanning transmission electron microscopy (STEM) in conjunction with electron energy-loss spectroscopy (EELS), with the aim of determining the role of A-site composition changes. At low La content (x = 0.2), adopting Pbnm symmetry, there was no indication of long-range ordering. Domains, with clear boundaries, were observed in bright-field (BF) imaging, but were not immediately visible in the corresponding high-angle annular dark-field (HAADF) image. These boundaries, with the aid of displacement maps from A-site cations in the HAADF signal, are shown to be tilt boundaries. At the La-rich end of the composition (x = 0.9), adopting Cmmm symmetry, long-range ordering of vacancies and La3+ ions was observed, with alternating La-rich and La-poor layers on (001)p planes, creating a double perovskite lattice along the c axis. These highly ordered domains can be found isolated within a random distribution of vacancies/La3+, or within a large population, encompassing a large volume. In regions with a high number density of double perovskite domains, these highly ordered domains were separated by twin boundaries, with 90° or 180° lattice rotations across boundaries. The occurrence and characteristics of these ordered structures are discussed and compared with similar perovskite systems.

Submitted by Rosivalda Pereira (mrs.pereira@ufma.br) on 2017-05-05T19:36:02Z No. of bitstreams: 1 AnaQueirozSilva.pdf: 6863169 bytes, checksum: e47ae4d9bb4d9f8cffde413e5eecd620 (MD5) Made available in DSpace on 2017-05-05T19:36:02Z (GMT). No. of bitstreams: 1 AnaQueirozSilva.pdf: 6863169 bytes, checksum: e47ae4d9bb4d9f8cffde413e5eecd620 (MD5) Previous issue date: 2016-07-19 In recent years, research has increased in order to develop new materials processing methods have more advantages over conventional methods currently used which are quicker and cheaper. It has become common to use ceramics to obtain electronic devices, dielectric or piezoelectric. The CaTiO3 ceramic material has been widely used in electronic devices. The objective of this study was to synthesize and characterize perovskite ceramic-based CaTiO3 (Titanate Calcium) replaced with rare earths. The synthesis and replacement of perovskite were made from the starting materials Ca(OH)2, TiO2, Er2O3 and Yb2O3 by mechanical milling in a ball mill for 30 min at 250 rpm to homogenization and then was taken calcination in a muffle furnace. The obtained material powder showed perovskite phase to the orthorhombic space group Pbnm 62. The unit cell of the crystal lattice parameters showed a = 5.378 Å, b = 5.441 Å and c = 7.640 Å for the CaTiO3, which has four per unit cell formula. The number and type of modes provided for each frame can be given by the factor groups having a total of 24 vibrational modes Raman for CaTiO3 with said structure. The morphological characteristics were observed for the samples CTO (calcium titanate) prepared by solid state reaction, demonstrating the formation of small, round grain vacancies, which may be caused by distortions in the crystal lattice. The CTO replaced with Er2O3 and Yb2O3 showed typical bands of green light at 525 and 547 nm corresponding to the transition 4H11/2 → 4I15/2. The two smaller emission bands in the red, correspond to transition 4F9/2 to the ground state 4I15/2. The results obtained for the ceramic systems were satisfactory as the method used for synthesis, who presented with lower cost compared to existing processes. Nos últimos anos, as pesquisas têm aumentado com o propósito de desenvolver novos métodos de processamento de materiais que apresentem mais vantagens em relação aos processos convencionais utilizados atualmente e que sejam mais rápidos e baratos. Tem se tornado comum utilizar cerâmicas para a obtenção de dispositivos eletrônicos, dielétricos ou piezoelétricos. O material cerâmico CaTiO3 tem sido amplamente utilizado em dispositivos eletrônicos. O objetivo deste trabalho foi sintetizar e caracterizar cerâmicas perovskitas à base de CaTiO3 (Titanato de Cálcio) substituída com terras raras. A síntese e a substituição da perovskita foram feitas à partir dos materiais de partida Ca(OH)2, TiO2, Er2O3 e Yb2O3 por moagem mecânica em um moinho de bolas por 30 min, a 250 rpm para homogeneização e em seguida, foi feita calcinação em um forno tipo mufla. O pó obtido do material apresentou fase de perovskita com grupo espacial ortorrômbica Pbnm 62. A célula unitária da rede cristalina apresentou os parâmetros a=5,378 Å, b=5,441 Å e c=7,640 Å para o CaTiO3, a qual possui quatro fórmulas por célula unitária. O número e tipo de modos previstos para cada estrutura pode ser dado pelo fator de grupos, havendo um total de 24 modos vibracionais Raman para o CaTiO3 com a estrutura citada. Foram observadas as características morfológicas para as amostras de CTO (Titanato de Cálcio), preparadas por reação no estado sólido, demonstrando a formação de grãos pequenos e redondos com vacâncias, que podem ser causadas por distorções na rede cristalina. O CTO substituído com Er2O3 e Yb2O3 apresentou bandas típicas da luz verde em 525 e 547 nm que correspondem à transição 4H11/2→4I15/2. As duas bandas menores de emissão no vermelho, correspondem à transição 4F9/2 para o estado fundamental 4I15/2. Os resultados obtidos para os sistemas cerâmicos mostraram-se satisfatórios quanto ao método utilizado para síntese, que, apresentou-se com menor custo comparado aos processos existentes.

Oxygen permeation measurements were performed on dense symmetric samples of Ca0.5Sr0.5Ti0.6Fe0.15Mn0.25O3−δ and compared to CaTi0.6Fe0.15Mn0.25O3−δ in order to assess the influence of the perovskite lattice volume on oxygen permeation. Oxygen flux measurements were performed in the temperature range 700–1000 °C and as function of feed side pO2 from 10−2 to 1 bar, and at high pressures up to 4 bar with a pO2 of 3.36 bar. The O2 permeability of the Sr-doped sample was significantly lower than that of the Sr-free sample, amounting to 3.9×10−3 mL min−1 cm−1 at 900 °C for a feed side pO2 of 0.21 bar. The O2 permeability of CaTi0.6Fe0.15Mn0.25O3−δ shows little variation with increased feed side pressures and reaches 1.5×10−2 mL min−1 cm−1 at 900 °C for a feed side pO2 of 3.36 bar. This is approximately 1.5 times higher than the O2 permeability with a feed side pO2 of 0.21 bar. Furthermore, in order to assess the applicability of CaTi0.6Fe0.15Mn0.25O3−δ as an oxygen membrane material, creep tests were performed under compressive loads of 30 and 63 MPa, respectively, in air in the temperature range 700–1000 °C; the results indicate a high creep resistance for this class of materials. The measured O2 permeabilities and creep rates are compared with other state-of-the-art membrane materials and their performance for relevant applications is discussed in terms of chemical and mechanical stability.

We investigate the structural and electronic properties of domain walls to achieve a better understanding of the conduction mechanisms in domain walls of lithium niobate and the polarity of domain walls in calcium titanate. In a first part, we discuss the interaction between defects and domain walls in lithium niobate. A dielectric resonance with a low activation energy is observed, which vanishes under thermal annealing in monodomain samples while it remains stable in periodically poled samples. Therefore we propose that domain walls stabilize polaronic states. We also report the evolution of Raman modes with increasing amount of magnesium in congruent lithium niobate. We identified specific frequency shifts of the modes at the domain walls. The domains walls appear then as spaces where polar defects are stabilized. In a second step, we use mirror electron microscopy (MEM) and low energy electron microscopy (LEEM) to characterize the domains and domain walls at the surface of magnesium-doped lithium niobate. We demonstrate that out of focus settings can be used to determine the domain polarization. At domain walls, a local stray, lateral electric field arising from different surface charge states is observed. In a second part, we investigate the polarity of domain walls in calcium titanate. We use resonant piezoelectric spectroscopy to detect elastic resonances induced by an electric field, which is interpreted as a piezoelectric response of the walls. A direct image of the domain walls in calcium titanate is also obtained by LEEM, showing a clear contrast in surface potential between domains and walls. This contrast is observed to change reversibly upon electron irradiation due to the screening of polarization charges at domain walls., Ce travail de thèse porte sur les propriétés structurales et électroniques des parois de domaines ferroïques ; il a pour objectif une meilleure compréhension des mécanismes de conduction dans les parois de domaines du niobate de lithium d’une part, et de la polarité des parois de domaine dans le titanate de calcium d’autre part. La première partie est consacrée aux interactions entre les défauts et les parois de domaine dans le niobate de lithium. L’observation d’une relaxation diélectrique de faible énergie d’activation et l’analyse de son comportement sous l’effet d’un recuit dans des échantillons avec et sans parois nous conduisent à proposer que les parois de domaines stabilisent des états polaroniques. Nous rapportons aussi l'évolution de modes Raman dans des échantillons congruents de niobate de lithium dopés de manière croissante en magnésium. Nous identifions des décalages en fréquence spécifiques aux parois de domaines. Les parois de domaines apparaissent alors comme des lieux de stabilisation des défauts polaires. Nous utilisons la microscopie électronique miroir (MEM) et la microscopie électronique de faible énergie (LEEM) pour caractériser les domaines et parois de domaines à la surface du niobate de lithium dopé magnésium. Nous démontrons que les réglages de la distance focale peuvent être utilisés pour déterminer la polarisation du domaine. Aux parois de domaines, un champ électrique latéral, provenant de différents états de charge de surface, est mis en évidence. Dans une seconde partie, nous étudions la polarité des parois de domaine dans le titanate de calcium. Nous utilisons la spectroscopie de résonance piézo-électrique pour mettre en évidence l’excitation de résonances élastiques par un signal électrique, ce qui est interprété comme une réponse piézoélectrique des parois de domaines. Une image directe des parois de domaine du titanate de calcium est obtenue par LEEM, et montre une différence de potentiel de surface entre domaines et parois. Ce contraste peut être modifié sous l’effet d’injection d’électrons, par un effet d’écrantage des charges de polarisation aux parois.

An effective interatomic potential which can be used to describe perovskite-type CaTiO 3 in molecular dynamics (MD) simulations is proposed. The potential proposed consists of two-body interactions, which include steric repulsions due to atomic sizes, Coulomb interactions resulting from charge transfer between particles, and charge-induced dipole interactions due to the electronic polarizability of ions and dipole–dipole (van der Waals) attraction. The energetics of the three crystalline forms of CaTiO 3 were calculated: the orthorhombic- Pbnm structure had the lowest energy, followed by the tetragonal- I4 / mcm and cubic- Pm3m structures. The two phase transitions induced by temperature change were characterized through anomalies in the lattice parameters, elastic constants, bulk modulus, bond-angle distribution and the intensity of the first peak of the partial pair distribution function, g Ca–O ( r ). Analysis of the pair distribution function is a sensitive means of detecting structural transformation in materials caused by small distortions. It is shown that the rise in structural symmetry with temperature is actually due to the tilting of the TiO 6 polyhedra. The response of the system to external pressure was also analyzed. Extremely high pressure, up to 300 GPa, was applied and no significant modification attributable to a major structural change was observed. The proposed interatomic potential is in good agreement with experimental data, predicting the melting point, phonon vibrational density of sates, thermal expansion coefficient and specific heat at constant volume. The recrystallized polycrystalline CaTiO 3 was reproduced in the simulation by cooling the liquid. It is shown that the presence of grain boundaries in the material is essential to reproduce the experimental data correctly.

Made available in DSpace on 2018-11-27T02:38:03Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-12-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) FAPEG Praseodymium-doped calcium titanate, CaTiO3:Pr3+, powders (0 and 2 mol% Pr3+ ions) were synthesized using the polymeric precursor and microwave-assisted hydrothermal methods. Both methods appear to be efficient in preparing photoluminescence materials because they require low temperatures and very short reaction times. Several characterization techniques were used to evaluate the influence of structural disorder on the reactions and properties of the materials produced. X-ray diffraction and Rietveld refinement were used to confirm that syntheses were successful. Raman spectroscopy revealed significant details of the structures of the materials produced. FE-SEM images were used to determine the shapes and dimensions of the products. Morphologies were found to be dependent on the synthesis method used. PL spectra showed Pr3+ emission lines at approximately 612 nm when the CT:Pr3+ powders were excited with a 350.7 nm laser. These lines correspond to D-1(2)-> H-3(4) transitions. (C) 2015 Elsevier Ltd and Techna Group Sr.!. All rights reserved. UNIFESP Univ Fed Sao Paulo, BR-09972270 Diadema, SP, Brazil LIEC Univ Fed Sao Carlos, BR-13565905 Sao Carlos, SP, Brazil LIEC IQ Univ Estadual Paulista, BR-14801907 Araraquara, SP, Brazil UFG Univ Fed Goias, Dept Quim CAC, BR-75704020 Catalao, Go, Brazil LIEC IQ Univ Estadual Paulista, BR-14801907 Araraquara, SP, Brazil CNPq: 573636/2008-7 FAPESP: 2013/07437-5 FAPESP: 2008/57872-1 FAPESP: 2013/07296-2 FAPEG: 35.0247/2010.2

Made available in DSpace on 2018-11-26T17:55:37Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-09-01 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) For this research, we studied the influence of titanium tetrachloride (TC) and titanium tetraisopropoxide (TTP) precursors on CaTiO3 (CTO) synthesis by employing a microwave-assisted hydrothermal (MAH) method regarding their respective short-, medium- and long-range features to determine if the use of different titanium precursors enhances the structural evolution of the material. The growth mechanism for the formation of the micro-cube-shaped CTO is proposed to obtain nanoparticle aggregation of self-assembly nanoplates. The disorder coupled to the oxygen vacancies of [TiO5]-[TiO6] in complex clusters in the CTO 1 powder and twists in bonding between the [TiO6]-[TiO6] complex clusters in the CTO 2 powder were mainly responsible for photoluminescent (PL) emission. (C) 2015 Elsevier B.V. All rights reserved. Univ Fed Sao Paulo, Dept Ciencias Mar, BR-11030400 Santos, SP, Brazil Univ Fed Pelotas, Inst Fis & Matemat, BR-96001970 Pelotas, RS, Brazil Univ Fed Sao Carlos, Dept Fis, BR-13565905 Sao Carlos, SP, Brazil Univ Sao Paulo, Inst Fis Sao Carlos, BR-13566590 Sao Carlos, SP, Brazil Univ Estadual Paulista, Inst Quim, INCTMN LIEC, BR-14801907 Araraquara, SP, Brazil Univ Estadual Paulista, Inst Quim, INCTMN LIEC, BR-14801907 Araraquara, SP, Brazil FAPESP: 2008/5787-1 CNPq: 573636/2008-7 FAPESP: 2013/07296-2

Oxygen permeation measurements are performed on dense samples of CaTi 0.85 Fe 0.15 O 3− δ , CaTi 0.75 Fe 0.15 Mg 0.05 O 3− δ and CaTi 0.75 Fe 0.15 Mn 0.10 O 3− δ in combination with density functional theory (DFT) calculations and X-ray photoelectron spectroscopy (XPS) in order to assess Mg and Mn as dopants for improving the O 2 permeability of CaTi 1− x Fe x O 3− δ based oxygen separation membranes. The oxygen permeation measurements were carried out at temperatures ranging between 700 and 1000 °C with feed side oxygen partial pressures between 0.01 and 1 bar. The O 2 permeability was experimentally found to be highest for the Mn doped sample over the whole temperature range, reaching 4.2×10 −3 ml min −1 cm −1 at 900 °C and 0.21 bar O 2 in the feed which corresponds to a 40% increase over the Fe-doped sample and similar to reported values for x =0.2. While the O 2 permeability of the Mg doped sample was also higher than the Fe-doped sample, it approached that of the Fe-doped sample above 900 °C. According to the DFT calculations, Mn introduces electronic states within the band gap and will predominately exist in the effectively negative charge state, as indicated by XPS measurements. Mn may therefore improve the ionic and electronic conductivity of CTF based membranes. The results are discussed in terms of the limiting species for ambipolar transport and O 2 permeability, i.e., oxygen vacancies and electronic charge carriers.

Ca1-xLa xTiO3 powders were prepared by the polymeric precursor method. X-ray diffraction (XRD), FT-Raman spectroscopy, transmission electron microscopy (TEM), and N2 and CO2 adsorption were used for the microstructural and surface characterization of the powders. Room temperature photoluminescence (PL) was observed in Ca1-xLa xTiO3 amorphous particles. The PL intensity of these powders was found to be dependent on the lanthanum molar concentration.

Amostras estruturalmente ordenadas e desordenadas de CaTiO3:X com X= Tb e/ou Yb foram estequiometricamente preparadas pelo método dos precursores poliméricos. A estrutura cristalina da amostra dopada foi analisada pelas medidas de difração de raios X. O padrão de difração obtido para as amostras estruturalmente ordenadas revelou uma única fase relacionada a fase perovsquita do tipo ortorrômbica do material. A difração de raios X também foi utilizada para avaliar a ordem-desordem estrutural dos materiais calcinados a diferentes temperaturas, bem como para calcular os parâmetros de rede e tamanho do cristalito dos materiais. Espectros de XANES foram utilizados para avaliar a ordem local ao redor dos átomos de Ti e correlacionar a altura da pré-borda com a presença de clusters de TiO5-TiO6. A propriedade fotoluminescente dos materiais obtidos foi investigada para os materiais calcinados em diferentes temperaturas, observando uma maior emissão fotoluminescente para o material tratado termicamente a 500ºC. Crystalline samples of CaTiO3: X with X = Tb or/and Yb were stoichiometrically prepared by the polymeric precursor method. The structure of the doped sample was analyzed by X-ray diffraction measurements. The diffraction pattern showed a single phase perovskite-related type orthorhombic. The X-ray diffraction was used to evaluate order-disorder materials calcined at different temperatures, and to calculate the lattice parameters and crystallite size of the materials. XANES spectra were used to evaluate the local order around the Ti atoms and correlating with pre presence of clusters TiO5-TiO6. The photoluminescent property of the obtained materials was investigated for the powders calcined at different temperatures and observed a greater issue for photoluminescent material heat treated at 500 ° C.

International audience; A conventional solid-state reaction has been used to synthesize the perovskite Ca(1 − x)SrxTi(1 − y)ZryO3 (y = 0.1). The aim of this study is focused on the development of new materials with complex perovskite structure and on their dielectric property improvement. The temperature and substitutional ratio effects on the different phase evolutions is investigated by X-ray diffraction (XRD) and scanning electron microscope observations. These ceramics sintered at 1500 °C, present a density higher than 95% and their dielectric properties are significantly affected by the substitution. The CaTiO3 ceramic present a relative permittivity of 190 and the temperature coefficient of the permittivity of − 1828 ppm/C°. The substitution with zirconium (for x = 0 and y = 0.1: Σ = 145; |Σ = − 917 ppm/C°). Both permittivity and temperature coefficient values decrease; however, an opposite effect is observed when substituting with the strontium. With increasing an x value and maintaining a y value constant (y = 0.1), the dielectric constant increases and the temperature coefficient remains constant. Therefore, the dielectric properties of CaTiO3 ceramics are improved with the combined substitution.

Three ceramic systems, CaTiO3 (CTO), CaCu3Ti4O12 (CCTO) and intermediate nonstoichiometric CaTiO3/CaCu3Ti4O12 mixtures (CTO.CCTO), were investigated and characterized. The ceramics were sintered at 1100 °C for 180 min. The surface morphology and structures were investigated by XRD and SEM. Elastic modulus and hardness of the surfaces were studied by instrumented indentation. It was observed that CCTO presented the higher mechanical properties (E = 256 GPa, hardness = 10.6 GPa), while CTO/CCTO mixture showed intermediate properties between CTO and CCTO. Fil: Ramírez, M. A.. Universidade Estadual Paulista Julio de Mesquita Filho; Brasil Fil: Parra, Rodrigo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones En Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones En Ciencia y Tecnología de Materiales; Argentina Fil: Reboredo, Maria Marta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones En Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones En Ciencia y Tecnología de Materiales; Argentina Fil: Varela, J. A.. Universidade Estadual Paulista Julio de Mesquita Filho; Brasil Fil: Castro, Miriam Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones En Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones En Ciencia y Tecnología de Materiales; Argentina Fil: Ramajo, Leandro Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones En Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones En Ciencia y Tecnología de Materiales; Argentina

CaTiO3 powders were synthesized using both a polymeric precursor method (CTref) and a microwave-assisted hydrothermal (CTHTMW) method in order to compare the chemical and physical properties of the perovskite-based material as a function of the synthesis method. To this end, X-ray diffraction, Raman spectroscopy, inductively coupled plasma atomic emission spectroscopy and experimental Ti and Ca K-edge X-ray absorption near-edge structure spectroscopy, as well as measurements of photoluminescence (PL) emission, were used to characterize the typical bottom-up process of the CaTiO3 perovskite phase at different times. Detailed Rietveld refinements show a random polycrystalline distortion in the powder structure, which can be associated with the tilting (α angle < O–Ti–O) between adjacent TiO6 octahedra (intermediate range) for CTHTMW samples and an intrinsic TiO6 distortion (short range) in relation to the polymeric precursor CTref sample. These properties were further investigated by first-principles calculations based on the density functional theory at the B3LYP level. The relationship between this tilting on the PL profile is highlighted and discussed. Thus, a structural model derived from both experimental results and theoretical simulations reveals a close relationship between this tilting and the presence of intermediate energy states within the band gap which are mainly responsible for PL emissions.

Calcium titanate, CaTiO3, an important microwave dielectric material and one of major phases in synroc (synthetic rock), a titanate ceramic with potential application for fixation of high level nuclear waste was synthesized from calcium titanyl oxalate [CaTiO (C2O4)(2)-6H(2)O] (CTO) by employing microwave heating technique. CTO heated in microwave heating system in air at 500 degrees C for 1 h gave a perovskite, CaTiO3. The product obtained by heating of CTO in the same system at 700 degrees C for the same duration was however, much more crystalline. CaTiO3 obtained by the present method was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and BET surface area measurement.

Crystalline calcium titanate was synthesized by mechanical activation of a mixture of CaO, obtained by thermal treatment of CaCO3, and TiO 2 in anatase or rutile form, in a planetary ball mill for 30, 60, 120 and 240 min.. The effect of milling on the solid-state reaction was followed by X-ray diffraction. Changes in powder size and morphology due to milling were determinate by SEM, while BET analysis was made to determine the specific surface area of powders. It was pointed out that the formation of calcium titanate was more easily achieved by mechanical activation synthesis of the mixture of calcium oxide and anatase modification of titanium oxide compared to the rutile form.