High-temperature EXAFS study of the tetragonal-to-cubic phase transition in compositionally homogeneous ZrO2-CeO2 nanopowders

L.M. ACUÑA; D.G. LAMAS; R.O. FUENTES; I.O. FÁBREGAS; N.E. WALSÖE DE RECA; R.J. PRADO; M.C.A. FANTINI; A.F. CRAIEVICH

2007 Activity Report of the Brazilian Synchrotron Light Laboratory

Laboratorio Nacional de Luz Sincrotrón (LNLS)

Año: 2008 p. 1117 - 1117

1518-0204

ZrO2-CeO2 solid solutions have been proposed as anodes in intermediate-temperature solid oxide fuel cells (IT-SOFCs) due to their excellent catalytical properties for direct oxidation of hydrocarbons. The investigation of the crystal and local structure of these materials is very useful for the understanding of their catalytical properties. In previous XPD and EXAFS studies at Brazilian Synchrotron Light Laborator (LNLS), we found a tetragonal-cubic transition as a function of composition, which is associated to a tetragonal-to-cubic symmetry change of the Zr-O bonding, while the Ce-O one has a cubic symmetry for all compositions. Considering that IT-SOFCs usually operates at temperatures in the range of 500-800°C, it is also important to study the phase transitions and changes in the local order as a function of temperature. In recent high-temperature XPD studies at LNLS, we found a tetragonal-to-cubic phase transition in ZrO2-50, 60 and 65 mol% CeO2 nanopowders and proposed a metastable phase diagram for nanostructured solid solutions. In this work, the features of the cation-oxygen bonding in compositionally homogeneous ZrO2-50 and 65 mol% CeO2 nanopowders as a function of temperature were studied, including the range at which the tetragonal-to-cubic transition occurs (700-850°C). To our knowledge, this transition has not been investigated by high-temperature EXAFS before. As in the case of our EXAFS study as a function of composition, it was found that the high-temperature tetragonal-to-cubic phase transition is related to a change in the local order around Zr cations.