High temperature magnetic properties of transition metal oxides with perovskite structure

Abstract

In recent years, transition metal oxides with perovskite structure have drawn considerable interest as mixed ionic electronic conductors (MIECs) that can conduct electrons and ions at high temperatures. Many phenomena of interest in perovskites occur at high temperature including electronic and ionic transport, catalysis and chemical expansion. Electronic structure controls host of critical properties that are of technological importance including oxygen nonstoichiometry, electronic and ionic conductivity.In this work, we have designed an experimental method to measure magnetization of transition metal oxide perovskites at high temperatures (600°C--1000°C) as a function of oxygen partial pressure. High temperature magnetic measurements were used to study electronic structure in two promising transition metal oxide perovskites for intermediate temperature solid oxide fuel cells: La 1-xSrxCoO3-delta(LSC) and La1-xSrxFeO 3-delta(LSF). LSF has semiconducting behavior and many of its properties have been attributed to change in oxidation state of iron with changes in temperature and oxygen partial pressure. LSC, on the other hand, has many properties that point towards metallic behavior at high temperatures.We find that at high temperatures, the oxygen nonstoichiometry and temperature dependence of magnetic susceptibility could be explained within the framework of localized electronic defects for LSF. In Contrast, the magnetic property of LSC at high temperatures suggest co-existence of localized and delocalized electronic states. We discuss this behavior in the context of existing electronic structure models, as well as transport properties.