Garcés, Diana A. (2012) Estudio de perovskitas LaBaCo_2O_6-delta: propiedades de alta temperatura y su evaluación como potenciales materiales para celdas de combustible o electrolíticas de óxido sólido. / A research on perovskites LaBaCo_2O_6-delta: high temperature properties and potential applications as fuel cells or solid-oxide electrolitic cells. Maestría en Ciencias Físicas, Universidad Nacional de Cuyo, Instituto Balseiro.
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Resumen en español
En esta tesis se estudia la influencia del método de síntesis para la obtención de las estructuras perovskitas con ordenamiento catiónico, LaBaCo_2O_6-δ, y sin él, La_0.5Ba_0.5CoO_3-δ. Se realiza un estudio de las propiedades de alta temperatura de estos compuestos y se los evalúan como potenciales materiales para celdas de combustible o electrolíticas de óxidos sólido. En la primera parte de esta tesis se obtienen las fases ordenada (LaBaCo_2O_6-δ) y desordenada (La_0.5Ba_0.5CoO_3-δ) mediante el método de síntesis de Reacción de Estado Sólido. Utilizando de manera combinada técnicas de difracción de rayos X (DRX), difracción de neutrones (DNP) y termogravimetría se realiza un estudio detallado de sus propiedades estructurales. Para el análisis de los datos de DRX y DNP se utiliza el método de Rietveld, donde se prueban diferentes modelos de refinamiento, obteniendo información estructural como por ejemplo parámetros de red, tensiones, vibraciones atómicas, distancias y ángulos entre enlaces, etc. Estos resultados se combinan con los obtenidos del análisis de las propiedades de transporte eléctrico consiguiendo así información sobre el mecanismo de conducción eléctrica, tipo de portadores, ordenamiento de vacancias de oxígeno, etc. En la segunda parte, se busca obtener las fases ordenada y desordenada pero a través de otro método de síntesis, aplicando técnicas de sol-gel partiendo de acetatos y realizando una policondensación con Acetil Acetona y Hexametiltetramina. Este método, llamado HMTA, permitiría conseguir dichas fases en condiciones más suaves de temperatura y/o tiempo y con menor tamaño de cristalita, lo cual mejoraría sus propiedades como cátodo. En esta búsqueda se preparan muestras obtenidas bajo diferentes condiciones de síntesis (variando temperatura, tiempo de síntesis y atmósfera) a las que se les realiza un estudio detallado de la estructura utilizando de manera combinada las técnicas de DRX y HR-TEM. Se intenta comprender la manera en que se produce el ordenamiento catiónico de las muestras a partir de fases intermedias. En la tercera parte de esta tesis se investigan los mecanismos limitantes de la reacción de reducción de oxígeno en los compuestos con y sin ordenamiento catiónico obtenidos mediante el método RES y en el compuesto sintetizado mediante el método de síntesis HMTA a 900 °C en argón (900Ar). Para realizar este estudio se utiliza la técnica de espectroscopía de impedancia electroquímica (EIS) en celdas simétricas electrodo/electrolito/electrodo. Se examinan diferentes condiciones de temperatura y presión parcial de oxígeno con el objetivo de determinar los mecanismos que controlan la reacción de electrodo. Para finalizar se detallan las conclusiones del trabajo realizado, analizando la aplicabilidad de las muestras como materiales para celdas de combustible o electrolíticas de óxidos sólido.
Resumen en inglés
In this thesis, the influence of synthesis method to obtain perovskites with cationic order, LaBaCo_2O_6-δ, and without it, La_0.5Ba_0.5CoO_3-δ, is studied. The high temperature properties of these compounds are analyzed and they are evaluated as potential materials for fuel or electrolytic solid oxide cells. First, ordered (LaBaCo_2O_6-δ) and disordered (La_0.5Ba_0.5CoO_3-δ) phases are obtained by Solid State Reaction (SSR). Their structural properties are studied in detail by combining XRD, NPD and TGA techniques. For diffraction data analysis the Rietveld’s method is used by essaying different refinement models and obtaining structural information such as lattice parameters, stresses, atomic vibrations, bond distances and angles, etc. This information is combined with results from electric transport experiments for determining the electric conduction mechanism, type of charge carriers, ordering of vacancies, etc. In the second part, the obtaining of ordered and disordered phases is looked by means of another synthesis method, applying sol-gel techniques staring from acetates and performing a poly-condensation with AcAc and hexametiltetramine. This method, called HMTA, would allow preparing these phases at lower temperatures and/or shorter times, with smaller crystallite sizes, which would improve their properties for cathode materials. In this search, different batches of samples are obtained under different annealing conditions (temperature, time and atmosphere); their structures are analyzed in detail by combining XRD and HR-TEM. The possible path followed for ordering or disordering, from intermediate phases, is discussed. In the third part of this thesis, the rate limiting steps of oxygen reduction reaction are evaluated on ordered and disordered compounds obtained by SSR and the one prepared by HMTA and annealed at 900ºC in Ar. This analysis is made by Electrochemical Impedance Spectroscopy (EIS) on symmetric electrode/electrolyte/electrode cells. The EIS experiments are carried out at different temperatures and oxygen partial pressures with the aim of determining the mechanisms that control the electrode reaction. At the end, the conclusions of the complete study are summarized, analyzing the applicability of these materials as electrodes for fuel or electrolytic solid oxide cells.
| Tipo de objeto: | Tesis (Maestría en Ciencias Físicas) |
|---|---|
| Palabras Clave: | Perovskite; Perovskita; Fuel Cells; Celulas de combustible; Solid oxide fuel cells; Celulas de combustible oxido solido; X-ray diffraction; Difracción de rayos X; Neutron diffraction; Difracción de neutrones; Acetylacetone; Acetilacetona; Hexametiltetramine; Hexametiltetramina |
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| Materias: | Física > Física de materiales |
| Divisiones: | Aplicaciones de la energía nuclear > Tecnología de materiales y dispositivos > Caracterización de materiales |
| Código ID: | 390 |
| Depositado Por: | Marisa G. Velazco Aldao |
| Depositado En: | 14 Feb 2013 11:13 |
| Última Modificación: | 14 Feb 2013 11:13 |
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