Redox energetics and enthalpy increments of GdBaCo2O6-δ

Abstract

The enthalpy increments for the GdBaCo2O6-δ double perovskite were determined by means of drop calorimetry in air in the temperature range between 365.4 K and 1272.4 K. The heats of orthorhombic I→orthorhombic II phase transition at 347.2 K and orthorhombic II→tetragonal transition at 745.8 K are equal to (2.95 ± 0.07) kJ·mol−1 and (2.40 ± 0.09) kJ·mol−1, respectively, as measured with differential scanning calorimetry for GdBaCo2O6-δ. These calorimetric data were used to determine the heat capacity of GdBaCo2O6-δ and the high-temperature ‘chemical’ contribution to the enthalpy increments, caused by the oxygen exchange. The differentiation of the ‘chemical’ contribution with respect to oxygen nonstoichiometry yielded the partial molar enthalpy of oxygen in the GdBaCo2O6-δ, which agrees well with the previously reported results. The enthalpy increment data of nonstoichiometric oxides have proven itself as a valuable source of redox energetics information.