Oxygen mobility in LaCoO3 perovskites

This work reports a study of oxygen mobility in a variety of LaCo1−xFexO3 perovskites. The methods used to evaluate oxygen reactivity were temperature programmed oxygen desorption and oxygen isotopic exchange. Three kinds of oxygen are distinguished, depending on their reactivities. First, surface oxygens were found to be the most active forms of oxygen. In oxygen desorption experiments, they are responsible for two desorption peaks, designated as α1- and α2-oxygens in this work. Grain boundary oxygen is distinguished from bulk oxygen, and is proposed to be responsible for β-oxygen desorption observed at high temperature (>750 °C). These two kinds of oxygen, surface and grain boundary oxygen, are however quickly exchanged with the gaseous oxygen during the isotopic exchange reaction. The third kind, and less reactive, oxygen species is proposed to be the bulk oxygen. The mobility of this oxygen in the bulk of LaCoO3 is measured by the initial rate of isotopic exchange. Its mobility is related to the activation of the bulk Co3+, and migration of some anionic vacancies.