A determination of the oxygen non-stoichiometry of the oxygen storage material YBaMn2O5+delta

摘要

The A-site ordered double-perovskite oxide, YEaMn(2)O(5+delta), has been of recent interest for possible application as an oxygen storage material. In the present study, the oxygen non-stoichiometry of YBaMn2O5+delta has been determined as a function of pO(2) at 650, 700 and 750 degrees C by Coulometric titration at near-equilibrium conditions. The results confirm that this perovskite oxide has three distinct phases on oxidation/reduction with delta approximate to 0, 0.5 and 1. The stabilities of the YBaMn2O5+delta phases span a wide range of oxygen partial pressures (similar to 10(-20) <= pO(2)(atm) <= similar to 1) depending on temperature. The phases interconvert at higher pO(2) values at higher temperatures. The partial molar free energies (Delta mu(o)) corresponding to the oxidation of YBaMn2O5 to YBaMn2O5.5 and of YBaMn2O5.5 to YBaMn2O similar to 6 were determined. The value of Delta mu(o) in both oxidation steps becomes less negative with increasing temperature. At some T and pO(2) conditions, YEaMn(2)O(5+delta) is unstable with respect to decomposition to BaMnO3-delta and YMnO3. This instability is anticipated from the previous studies of the synthesis of YBaMn2O5+delta but is more apparent in the present experiments which are necessarily slow in order to achieve equilibrium with respect to the oxygen content. (C) 2015 Elsevier Inc. All rights reserved.