High-Resolution Thermochemical Study of Phase Stability and Rapid Oxygen Incorporation in YBaCo4- xZn xO7+δ 114-Cobaltites.

The formation thermodynamics of YBaCo4- xZn xO7+δ ( x = 0, 1, and 3) oxides was determined by high-temperature oxide melt solution calorimetry. All of the studied oxides are thermodynamically metastable due to the tendency of cobalt to increase the oxidation state under oxidizing conditions as well as to significant bond valence sum mismatch for Ba and Y in 114-oxides. Complex phase evolution in YBaCo4O7+δ at 350-400 °C upon oxygen absorption was revealed using incremental precise oxygen dosing. The calorimetric results support phase changes seen during in situ X-ray diffraction structural studies and provide high-resolution measurement of the amount and energetics of oxygen absorbed by YBaCo4- xZn xO7+δ under equilibrium conditions.