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

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

Campinas

Encuentro; RAU 18; 2008

LNLS-CNPEM

ZrO2-CeO2 solid solutions have been proposed as anodes in intermediate-temperaturesolid oxide fuel cells (IT-SOFCs) due to their excellent catalytical propertiesfor direct oxidation of hydrocarbons. The investigation of the crystal andlocal structure of these materials is very useful for the understanding oftheir catalytical properties. In previous XPD and EXAFS studies at BrazilianSynchrotron Light Laboratory (LNLS), we found a tetragonal-cubic transition asa function of composition, which is associated to a tetragonal-to-cubic symmetrychange of the Zr-O bonding, while the Ce-O one has a cubic symmetry for allcompositions. Considering that IT-SOFCs usually operates at temperatures in therange of 500-800ºC, it is also important to study the phase transitions andchanges in the local order as a function of temperature. In recent high-temperature XPD studies at LNLS, we found a tetragonal-to-cubic phasetransition in ZrO2-50, 60 and 65 mol% CeO2 nanopowders and proposed a metastable phase diagram for nanostructuredsolid solutions. In this work, the features of the cation-oxygen bonding in compositionally homogeneousZrO2-50 and 65 mol% CeO2 nanopowdersas a function of temperature were studied, including the range at which thetetragonal-to-cubic transition occurs (700-850ºC). To our knowledge, thistransition has not been investigated by high-temperature EXAFS before. As in thecase of our EXAFS study as a function of composition, it was found that thehigh-temperature tetragonal-to-cubic phase transition is related to a change inthe local order around Zr cations.