Sintering and microstuctural characterization of W6+, Nb5+ and Ti4+ iron-substituted BiFeO3

The sintering behaviour and the microstructural evolution of W6+, Nb5+ and Ti4+iron-substituted BiFeO3 ceramics have been analyzed. The obtained results show that W6+ and Nb5+ ions interact with the secondary phases usually present in these materials, thus altering the solid state formation of the BiFeO3 phase. In contrast, Ti4+ ions incorporate into the perovskite structure, leading to an exceptionally low proportion of secondary phases. In addition to this, BiFe0.95Ti0.05O3 materials present a dense microstructure with submicronic and nanostructured grains, clearly smaller than those in the undoped materials

Electrophoretic Deposition of Transparent ZnO Thin Films from Highly Stabilized Colloidal Suspensions

The parameters that control the stability of ZnO-nanoparticles suspensions and their deposition by electrophoretic deposition were studied, so as to organize the assembly and compaction of nanoparticles. The addition of cationic polyelectrolyte - Polyethylenimine (PEI) - with different molecular weights was investigated, in order to study their effectiveness and the influence of the molecular weight of the organic chain on suspensions dispersion. It was found that PEI with the highest molecular weight provided better dispersion conditions. Cathodic EPD was performed under previously optimized suspensions conditions and over electropolished stainless steel substrates. Experimental results showed that the EPD process in these conditions allows obtaining dense transparent ZnO thin films. Deposition times and intensities were optimized by analyzing the resulting thin films characteristics. Finally, the deposits were characterized by FE-SEM, AFM, and different spectroscopic techniques

Comparative study of two synthesis methods to obtain ZnO-Pr2O3-CoO ceramic powders

[ES] Los polvos cerámicos de ZnO - Pr2O3 - CoO son utilizados como materia prima para la fabricación de varistores. Estos dispositivos presentan una característica corriente - voltaje altamente no lineal que permiten su uso como conmutadores de estado sólido con capacidad de manejar altas energías. La discusión de las propiedades de los varistores no se puede realizar de manera separada de una discusión sobre su microestructura ya que ésta se puede considerar como un medio a través de la cual aquellas se manifiestan. Con el fin de optimizar las propiedades de los varistores de ZnO es necesario establecer un adecuado control sobre la composición del sistema, la naturaleza de los dopantes, métodos de síntesis y condiciones de sinterización. Concretamente, en métodos de síntesis, se han realizado muchos esfuerzos para desarrollar procesos que permitan obtener partículas con tamaño y morfología determinada y que se pueda garantizar su reproducibilidad. En este trabajo se estudiaron dos procesos de síntesis, co-precipitación y precursor polimérico, para la obtención de polvos cerámicos del sistema Zn-Pr-Co. Se analizaron los principales fenómenos fisicoquímicos que ocurren durante su desarrollo y se caracterizaron las muestras en polvo obtenidas utilizando Difracción de Rayos - X (DRX), Análisis Térmico Diferencial (ATD) y Microscopía Electrónica.[EN] Zinc oxide containing rare earth metal and Cobalt oxide are utilized as raw material to make varistors. Some of systems were found to exhibit non-ohmic current-voltaje characteristics and they are applicable not only for low voltaje devices but also for hight voltaje electric power stations. The microstructure of ZnO varistor can be considered as a vehicle thorugh which all of these properties ara manifested. Therefore, a discussion of the microstructure cannot be separated from a discussion of the properties. Fine particle dimensions and a narrow size distribution are often important aims when fabricating a ceramic material of a desired microstructure. Chemical methods give the ability to produce powders with an exceptionally small size in the nanometer range. In this paper we report the production of nanosized ZnO, doped with cobalt and Praseodymium oxides, using co-precipitation reaction and metallorganic polymeric method. Adequate description of synthesis methods and the characterization of ceramic powders obtained are show.Este trabajo fue realizado a través del proyecto COLCIENCIAS 1103-05-11507 Colombia (CYTED VIII.13 PROALERTA).Peer reviewe

Soft solution fluorine-free synthesis of anatase nanoparticles with tailored morphology

TiO2 nanoparticles with tailored morphology have been synthesized under exceptionally soft conditions. The strategy is based on the use of a non-aqueous alcoholic reaction medium in which water traces, coming either from the air (atmospheric water) or from an ethanol–water azeotropic mixture (ethanol 96%), are incorporated in order to accelerate hydrolysis of the Ti–precursor. Moreover, organic surfactants have been used as capping agents so as to tailor crystal growth in certain preferential directions. Combinations of oleic acid and oleylamine, which lead to the formation of another surfactant, dioleamide, are employed instead of fluorine-based compounds, thus increasing the sustainability of the process. As a result, TiO2 nanostructured hierarchical microspheres and individual nanoparticles with exposed high-energy facets can be obtained at atmospheric pressure and temperatures as low as 78 °C

Procedimiento de obtención de partículas de ZnO con morfología acicular

Referencia OEPM: P200001597.-- Fecha de solicitud: 27/06/2000.-- Titular: Consejo Superior de Investigaciones Científicas (CSIC).Procedimiento de obtención de partículas de ZnO con morfología acicular. La presente invención utiliza el método de precipitación controlada para obtener partículas de ZnO con morfología acicular. A través del control de los parámetros de formación de precursores intermedios de compuestos de cinc y la evolución de dichos precursores intermedios mediante el lavado con agua destilada de la suspensión coloidal se obtiene hidróxido de cinc. La destilación entre 100-150°C de una suspensión acuosa del hidróxido de zinc produce la formación de partículas de óxido de cinc con morfología acicular. El tamaño de las partículas varía con las condiciones de obtención, siendo el tamaño estándar de 0.5 μm de diámetro y 5-8 μm de longitud. La eficacia del procedimiento es superior al 90%.Peer reviewe

DiseNo de materiales basados en BaTiO3 con microestructura controlada aplicables como condensadores ceramicos multitapa

Centro de Informacion y Documentacion Cientifica (CINDOC). C/Joaquin Costa, 22. 28002 Madrid. SPAIN / CINDOC - Centro de Informaciòn y Documentaciòn CientìficaSIGLEESSpai

Diseño de materiales basados en BaTiO3 con microestructura controlada aplicables como condensadores cerámicos multitapa

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física de Materiales. Fecha de lectura: 23-6-9

Effect of ZnO on the microstructure and electrical properties of WO3-Bi4Ti3O12 ceramics

The aim of the present work is to explore the possibility of incorporate a small amount of ZnO to improve the microstructure control of W-doped BIT based materials. Two different processing routes have been used according to previous results reported for other materials: reaction and sintering in one single step and a previous calcination step. The sintering behaviour of the samples, the obtained crystalline phases and the microstructure analysis indicate that the reaction between ZnO and Bi2O3 plays a critical role during sintering. Both Bi2Ti2O7 and Zn2TiO4 secondary phases are stabilised when adding ZnO. Actually, when WO3 and ZnO are incorporated simultaneously to BIT materials, they interact stabilizing the Bi2Ti2O7 phase and avoiding the incorporation of W6+ into the BIT lattice. As a consequence, the electrical conductivity of the samples with ZnO is two orders of magnitude higher than that of the samples doped only with WO3, suggesting that WO3 does not form a solid solution with BIT. The curve dielectric constant vs temperature also reveals the role played by the Bi2Ti2O7 phase.Peer reviewe

“Estudio termodinámico de la región rica en Bi2O3 del sistema Bi2O3-ZnO.”

[EN] Precise knowledge of the Bi2O3-ZnO system is fundamental to control the functional microstructure of ZnO-based varistors. Also the potential applications of materials based on ZnO and Bi2O3 as dielectric materials in the high frequency range have renewed the interest in this binary system. The aim of the present work is to carry out a thermodynamic analysis of the Bi2O3-ZnO phase diagram, taking into account the existing experimental information. Thermodynamic calculation has been performed according CALPHAD methodology (CALculation of PHAse Diagrams), using the software Thermo-Calc.[ES] El conocimiento preciso del sistema Bi2O3-ZnO es una herramienta básica para conseguir el control de la microestructura de los varistores basados en ZnO. Recientemente otros materiales basados en óxidos de cinc y bismuto han mostrado un gran potencial para su uso en aplicaciones como dieléctricos a frecuencias altas, renovando el interés por dicho sistema binario. El objetivo del presente trabajo es realizar una evaluación termodinámica del diagrama de fases consistente para el sistema Bi2O3-ZnO teniendo en cuenta la información experimental existente del mismo. La evaluación termodinámica del sistema se ha llevado a cabo mediante la metodología CALPHAD (CALculation of PHAse Diagrams), empleando el software Thermo- Calc.Peer reviewe