Oxygen content and thermodynamic stability of YBaCo2O6-δdouble perovskite

Abstract

The thermodynamic stability of the double perovskite YBaCo2O6-δ was studied using the coulometric titration technique and verified by measurements of the overall conductivity depending on oxygen partial pressure at a given temperature. As a result, the stability diagram of YBaCo2O6-δ was plotted. YBaCo2O6-δ was found to be thermodynamically stable in air at 850°C and higher temperatures, whereas its thermodynamic stability at 900°C is limited by the range of oxygen partial pressures -3.56 ≤ log(pO2/atm) ≤ -0.14. Oxygen content in YBaCo2O6-δ slightly decreases at 900°C from 5.035 at log(pO2/atm) = -0.14 to 4.989 in the atmosphere with log(pO2/atm) = -3.565 indicating a crucial role which variation of Co+3/Co+2 ratio plays in its stability. YBaCo2O6-δ decomposes into the mixture of YCoO3 and BaCoO3-z at the high pO2 stability limit, whereas YBaCo4O7, BaCo1-xYxO3-γ, and Y2O3 were identified as the products of its decomposition at the low pO2 one.