High-temperature charge transport in Nd_0.25Sr_0.75FeO_3-δ: the influence of various factors

The oxygen content and electrical conductivity in Nd_0.25Sr_0.75FeO_3-δ were measured in the range of oxygen partial pressure from 10^-19 to 0.5 atm at 750-950 °C by coulometric titration and four-probe dc techniques. The thermodynamic analysis of defect equilibrium in the oxide allowed successful simulation of the oxygen content data and calculation of charge carrier concentrations that were used for the analysis of electrical conductivity. The electrical conductivity data were accurately described in the models, which implied that the hole mobility increased upon an increase in the oxygen content in the oxide. The results suggest that only some of the Fe³⁺ sites are available for hole transport, and their fraction increases with an increase in the oxygen content. The migration energy for oxygen ions, electrons and holes was found to be 0.89 ± 0.02, 0.62 ± 0.01 and 0.230 ± 0.006 eV, respectively. Nd_0.25Sr_0.75FeO_3-δ was shown to have a considerable oxygen conductivity (0.12 S cm^-1 at 950 °C) and fairly good stability under reducing conditions, which is a good recommendation for using this oxide as a functional material in high-temperature electrochemical applications.