Structural Reversibility of LaCo1-xCuxO3 Followed by In Situ X-ray Diffraction and Absorption Spectroscopy

Abstract

Combinations of perovskite-type oxides with transition andprecious metals exhibit a remarkable self-regenerable propertythat could be exploited for numerous practical applications. Theobjective of the present work was to study the reversibility ofstructural changes of perovskite-type oxides under cyclicreducing/oxidizing atmosphere by taking advantage of thereducibility of LaCoO3. LaCoO3 dand LaCo0.8Cu0.2O3 dwereprepared by ultrasonic spray combustion and were character-ized by scanning electron microscopy (SEM), X-ray diffraction(XRD), X-ray absorption spectroscopy (XAS) and temperature-programmed reduction (TPR). XRD and XAS data confirmed thatcopper adopted the coordination environment of cobalt at theB-site of the rhombohedral LaCoO3under the selected synthesisconditions. The structural evolution under reducing atmospherewas studied byin situXRD and XANES supporting the assign-ment of the observed structural changes to the reduction of theperovskite-type oxide from ABB’O3(B’=Cu) to B’0/ABO3and toB’0B0/A2O3. Successive redox cycles allowed the observation of anearly complete reversibility of the perovskite phase, i.e. copperwas able to revert into LaCoO3upon oxidation. The reversiblereduction/segregation of copper and incorporation at the B-siteof the perovskite-type oxides could be used in chemicalprocesses where the material can be functionalized bysegregation of Cu and protected against irreversible structuralchanges upon re-oxidation.