EXAFS determination of cation local order in layered perovskites

M. E. Montero–Cabreraª, M. García–Guaderrama^b, A. Mehta^c, S. Webb^c, L. Fuentes–Monteroª, J.A. Duarte Mollerª, and L. Fuentes–Cobasª

ª Centro de Investigación en Materiales Avanzados, Chihuahua, México.

^b Universidad Nacional Autónoma de México, México, D.F.

^c Stanford Synchrotron Radiation Laboratory, CA, USA.

Recibido el 14 de mayo de 2007
Aceptado el 26 de octubre de 2007

Abstract

EXAFS analysis of Bi₆Ti₃Fe₂O₁₈ Aurivillius ceramic was performed to elucidate the local environment of Fe cations. Experiments were performed at Stanford Synchrotron Radiation Laboratory, at T = 10, 30, 50, 75, 100 and 298 K, in fluorescence regime. EXAFS spectra were processed using the ab initio multiple scattering program FEFF6. Distances among representative atomic pairs were refined. As a basic result, the previous hypothesis suggested by X–ray diffraction experiments, regarding a preference of iron atoms for the centered perovskite layer of the unit cell, was confirmed.

Keywords: synchrotron radiation; EXAFS; Aurivillius ceramic; local order.

Resumen

Se determinó por EXAFS el entorno local de los cationes de hierro en la cerámica Aurivillius Bi₆Ti₃Fe₂O₁₈. La parte experimental de la investigación se realizó en el Laboratorio de Radiación Sincrotrónica de Stanford, en régimen de fluorescencia, a temperaturas de 10, 30, 50, 75, 100 y 298 K. Los espectros EXAFS fueron procesados mediante el software ab initio para dispersion múltiple FEFF6. Se refinaron las distancias inter–atómicas de pares representativos. Un resultado básico del trabajo es la confirmación de la hipótesis, sugerida por resultados de difracción de rayos x, relativa a la preferencia de los átomos de hierro por ocupar posiciones en la capa perovskita del nivel central en la celda unitaria.

Descriptores: radiacion sincrotrónica; EXAFS; cerámica de Aurivillius; orden local.

PACS: 61.10.Ht;77.84.–s

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Acknowledgements

Portions of this research were carried out at the Stanford Synchrotron Radiation Laboratory, a national user facility operated by Stanford University on behalf of the U.S. Department of Energy, Office of Basic Energy Sciences. The SSRL Structural Molecular Biology Program is supported by the Department of Energy, Office of Biological and Environmental Research, and by the National Institutes of Health, National Center for Research Resources, Biomedical Technology Program. Support from Consejo Nacional de Ciencia y Tecnología, CONACYT (Projects 42361 and 46515), is gratefully acknowledged.

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