120 research outputs found
Correlation between the spectroscopic and structural properties with the occupation of Eu3+ sites in powdered Eu3+-doped LiTaO3 prepared by the Pechini method
Characterization of lanthanum-doped bismuth titanate thin films prepared by polymeric precursor method
Abstract Lanthanum-modified bismuth titanate, Bi 4 À x La x Ti 3 O 12 (BLT), with x ranging from 0 to 0.75 was grown on Pt/Ti/SiO 2 /Si substrates using a polymeric precursor solution and spin-coating method. The dielectric constant of highly doped bismuth titanate was equal to 148 while dielectric losses remained low (tan d = 0.0018), and the films showed well-saturated polarization-electric field curves (2P r = 40.6 AC/cm 2 and V c = 0.99 V). The leakage current densities improve for the lanthanum-doped system. For five-layered BLT films with x = 0.75, a charge storage density of 35 fC/Am 2 and a thickness of 320 nm were found.
Influence of synthesis and processing parameters of the columbite precursor on the amount of Perovskite PMN
Study of k and LiNbO3 addition on the final properties of the relaxor pmn processed by powder blend
[ES] El relaxor cerámico PMN ha sido investigado por un gran número de investigadores en el transcurso del tiempo y muchos aspectos de este
material, como la morfologÃa de los polvos, descomposición de fases, pérdida de peso en el proceso de sinterización, densificación, entre
otras, siguen siendo objetos de investigación. La preparación de polvos de PMN se ha mostrado más efectiva cuando son sintetizados por la ruta de la columbita, pero la etapa de adición de plomo para la sÃntesis de polvos de PMN todavÃa sigue problemática. Por lo tanto, este trabajo propone una nueva asociación de metodologÃas, utilizando la ruta de la columbita y el método de precipitación por hidróxidos. Mediante la utilización de una técnica de mezcla de polvos, la cual permitió lograr buenas densidades en verde y sinterizadas, fue posible observar que los dopantes K+ y Li+ reducen las pérdidas de peso en el proceso de sinterización y cambian significativamente las propiedades dieléctricas. La adición de semillas de LiNbO3 en la etapa de conformación, las cuales reaccionan de modo distinto dependiendo del tamaño de las partÃculas, promueve la formación de granos de diferente tamaño en el cuerpo cerámico. Como consecuencia de esto, propiedades dieléctricas muy diferentes que en la cerámica PMN convencional son obtenidas.[EN] PMN ceramic relaxor has been investigated by several researchers and many aspects of this material, like powder morphology, phase
decomposition, weight loss during sintering process, densification, between others, still are investigated. PMN powder preparation has
been shown more efficient when synthesized by columbite route, however lead addition stage for the PMN powder synthesis remains problematic. Therefore, this work proposes a new association of methodologies, using columbite route and the hydroxide precipitation method. Through use of the powder mixture technique, which permitted to obtain good green and sintered densities, was possible to observe K+ y Li+ dopants reduce weight loss in sintering process and change significantly the dielectric properties. Addition of LiNbO3 seeds in conformation stage, which react in a distinct way as a function of the particle size, promotes the formation of differenced grains in the ceramic bulk. Consequently, very different dielectrics properties from conventional PMN ceramic were obtained.Peer reviewe
Influência do oxalato de amônio na formação do precursor columbita obtido pelo método Pechini
A rota da columbita para sÃntese do PMN (Pb3MgNb2O9) é um processo que permite reduzir significativamente a formação de fases secundárias. O método Pechini, utilizado na sÃntese da columbita, permite perfeita homogeneidade quÃmica e maior reatividade dos pós. Neste trabalho foi demonstrado como o controle dos parâmetros de sÃntese, impurezas e condição de calcinação podem afetar a obtenção de MN uma única fase cristalina MgNb2O6. Durante a etapa de decomposição da matéria orgânica, a presença do resÃduo oxalato de amônio elevou a temperatura de sÃntese do MN, reduzindo os valores da área superficial. Os resultados de TG/DTA e DRX indicaram que o mecanismo de formação da fase columbita é influenciado pela quantidade de resÃduo de oxalato de amônio existente na resina. O precursor columbita (MN), com monofase cristalina e grande reatividade superficial, foi obtido utilizando solução de citrato de nióbio completamente livre de impurezas e calcinação a 900°C por 2 horas
Effect of preannealing on the morphology of LiTaO 3 thin films prepared from the polymeric precursor method
Abstract Lithium tantalate (LiTaO 3 ) thin films with 50:50 stoichiometry were deposited on silicon (100) substrates with two layers by the spin coating method using a polymeric organic solution. In order to study the influence of preannealing on the crystallinity, microstructure, grain size and roughness of the final film, two annealing procedures, ''slow preannealing'' and ''fast preannealing,'' were used. X-ray diffraction (XRD) results showed that LiTaO 3 thin films are polycrystalline. It was observed by scanning electron microscopy (SEM) that the thin film, which had been thermally treated using slow preannealing, was characterized by a dense and homogeneous surface. The atomic force microscopy (AFM) studies showed that the roughness is strongly influenced by preannealing temperature.
Estudio de PMN cerámico dopado con KNbO<sub>3</sub> y LiNbO<sub>3</sub> sintetizado por Pechini
PMN belongs to a special class of materials named relaxor ferroelectrics. It has high volumetric efficiency due to its high dielectric constant, which makes it in a perfect material for application in multilayer capacitors. When prepared the columbite route its preparation has many advantages. In this work, the preparations of columbite and PMN were done by Pechini and Partial Oxalate methods, respectively. The effects of the KNbO3 and LiNbO3 dopants added in various concentrations. The idea is founded on the correlations that they have with BaTiO3 y PbTiO3, respectively. The whole process was supervised by TG/DTA, XRD, SEM and determination of the specific surface area of the powders. LiNbO3 carries out the pre-sinterization of the particles, observed by a reduction in the surface area. There are not particle grow, but occur its lengthening. However, for KNbO3 these particle growth, but the agglomerates are softer. The effect produced by the doping during the synthesis of the PMN powder is different from the one produced in the columbite precursor. Pure precursor shows an average particle size of 0,2μm, but the addition of 5,0mol% of dopants carries out the formation of agglomerates close to 4μm. LiNbO3 addition carries out spherical particles and pre-sinterization, while KNbO3 addition does not change the particles shape.El PMN pertenece a una clase especial de materiales conocido como ferroeléctricos relaxores. Posee gran eficacia volumétrica debido a su gran constante dieléctrica, siendo un perfecto candidato para la aplicación en capacitores multicapas. Su preparación es más ventajosa cuando se sintetiza por la ruta de la columbita. Las preparaciones de la columbita y del PMN se basaron en los métodos Pechini y Oxalato Parcial, respectivamente. Se ha estudiado los efectos de los dopantes KNbO3 y LiNbO3 añadidos a varias concentraciones. La idea esta basada en las correlaciones que estos tienen con BaTiO3 y PbTiO3, respectivamente. El proceso entero se caracterizó mediante ATD/TG, DRX, MEB y determinación de la superficie especÃfica de los polvos. El dopante LiNbO3 promueve la pre-sinterización de las partÃculas de MN, reduciendo la superficie especÃfica del polvo. No hay crecimiento de partÃcula, pero ocurre su alargamiento. En cambio, para el KNbO3 ocurre crecimiento de partÃcula, pero los aglomerados son más blandos. El efecto causado por los dopantes durante la sÃntesis de los polvos de PMN es diferente a los producidos en el precursor. El precursor puro presenta tamaño medio de partÃcula de 0,2μm, pero la adición de 5,0%molar de dopante produce la formación de aglomerados de ~4μm. La adición de LiNbO3 produce partÃculas arredondeadas y pre-sinterización, mientras la adición de KNbO3 no altera la forma de las partÃculas
Effect of the excess of bismuth on the morphology and properties of the BaBi2Nb2O9 thin films
In this study, the effect of bismuth content on the crystal structure, morphology and electric properties of barium bismuth niobate (BaBi2Nb2O9) thin films was explored with the aid of X-ray diffraction (XRD), scanning electron microcopy (SEM), atomic force microscopy (AFM) and dielectric properties. BaBi2Nb2O9 (BBN) thin films have been successfully prepared by the polymeric precursor methods and deposited by spin coating on Pt/Ti/SiO2/Si (100) substrates. The phase formation, the grain size and morphology of the thin films were influenced by the addition of bismuth in excess. It was observed that the formation of single phase BBN for films was prepared with excess of bismuth up to 2 wt%. The films prepared with excess of the bismuth showed higher grain size and better dielectric properties. The 2 wt% bismuth excess BBN thin film exhibited dielectric constant of about 335 with a loss of 0.049 at a frequency of 100 kHz at room temperature. (c) 2009 Elsevier Ltd and Techna Group S.r.l. All fights reserved.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento CientÃfico e Tecnológico (CNPq
Estudio de la adición de K<sup>+</sup> y LiNbO<sub>3</sub> en las propiedades finales del Relaxor PMN procesado por mezcla de polvos
PMN ceramic relaxor has been investigated by several researchers and many aspects of this material, like powder morphology, phase decomposition, weight loss during sintering process, densification, between others, still are investigated. PMN powder preparation has been shown more efficient when synthesized by columbite route, however lead addition stage for the PMN powder synthesis remains problematical. Therefore, this work proposes a new association of methodologies, using columbite route and the hydroxide precipitation method. Through use of the powder mixture technique, which permitted to obtain good green and sintered densities, was possible to observe K+ y Li+ dopants reduce weight loss in sintering process and change significantly the dielectric properties. Addition of LiNbO3 seeds in conformation stage, which react in a distinct way as a function of the particle size, promotes the formation of differenced grains in the ceramic bulk. Consequently, very different dielectrics properties from conventional PMN ceramic were obtained.<br><br>El relaxor cerámico PMN ha sido investigado por un gran número de investigadores en el transcurso del tiempo y muchos aspectos de este material, como la morfologÃa de los polvos, descomposición de fases, pérdida de peso en el proceso de sinterización, densificación, entre otras, siguen siendo objetos de investigación. La preparación de polvos de PMN se ha mostrado más efectiva cuando son sintetizados por la ruta de la columbita, pero la etapa de adición de plomo para la sÃntesis de polvos de PMN todavÃa sigue problemática. Por lo tanto, este trabajo propone una nueva asociación de metodologÃas, utilizando la ruta de la columbita y el método de precipitación por hidróxidos. Mediante la utilización de una técnica de mezcla de polvos, la cual permitió lograr buenas densidades en verde y sinterizadas, fue posible observar que los dopantes K+ y Li+ reducen las pérdidas de peso en el proceso de sinterización y cambian significativamente las propiedades dieléctricas. La adición de semillas de LiNbO3 en la etapa de conformación, las cuales reaccionan de modo distinto dependiendo del tamaño de las partÃculas, promueve la formación de granos de diferente tamaño en el cuerpo cerámico. Como consecuencia de esto, propiedades dieléctricas muy diferentes que en la cerámica PMN convencional son obtenidas
Structural characterization of 0.5PbMg(1/3)Nb(2/3)O(3)-0.5Ba(x)Pb((1-x))TiO(3) powders
The present work reports the effects caused by barium on phase formation, morphology and sintering of lead magnesium niobate-lead titanate (PMN-50PT). Ab initio study of 0.5PbMg(1/3)Nb(2/3)O(3)-0.5Ba(x)Pb((1-x))TiO(3) ceramic powders, with x = 0, 0.20, and 0.40 was proposed, considering that the partial substitution of lead by barium can reestablish the equilibrium of monoclinic-tetragonal phases in the system. It was verified that even for 40 mol% of barium, it was possible to obtain pyrochlore-free PMN-PT powders. The increase of the lattice parameters of PMN-PT doped-powders confirmed dopant incorporation into the perovskite phase. The presence of barium improved the reactivity of the powders, with an average particle size of 120 nm for 40 mol% of barium against 167 mn for the pure sample. Although high barium content (40 mol%) was deleterious for a dense ceramic, contents up to 20 mol% allowed 95% density when sintered at 1100 degrees C for 4 h. (c) 2007 Elsevier Ltd. All rights reserved
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