Oxygen doping in Ca1-xSrxFeO3-z perovskite oxides by an electrochemical method

Abstract

Oxygen doped Ca1-xSrxFeO3-z (0≤x≤1.0, z=0.25-0) perovskite type oxides were prepared by treating grossly oxygen-deficient samples using an electrochemical oxidation technique at room temperature. Although the oxygen-deficient starting samples in the Ca-rich region (CaFeO2.5 and Ca0.8Sr0.2FeO2.5) had high resistivity, it was possible to dope oxygen when a high current and a high electrode potential were applied. However, there is no reproducibility in preparing them. Ca1-xSrxFeO3-z in the Ca rich region (x=0.4-0.0) showed a gradual metal-insulator (MI) transition due to the charge disproportionation of Fe4+ (2Fe4+ ↔Fe3+ + Fe5+) below room temperature. For the oxygen doping of the perovskite oxides, applying only a few hundred mV of electrode potential creates the same effect as a long annealing at high oxygen pressure of more than a few hundred MPa. Although the lack of stability after electrolysis is a weak point, the electrochemical reaction is a simple and easy way to creates the oxygen doped state of the perovskite oxides.