Defect structure and thermochemistry of YBaCo2O6-δ

Abstract

The defect structure analysis of the oxygen deficient YBaCo2O6-δ double perovskite cobaltite confirms that the model proposed earlier for RBaCo2O6-δ (R – Pr, Gd, La) holds also for YBaCo2O6-δ. In particular, a good agreement between the pO2(T, δ) model function and experimental pO2 – T – δ data is obtained for this oxide. By means of high-temperature drop calorimetry, the enthalpy increments of YBaCo2O6-δ samples with different initial oxygen contents (0.67 ≤ δ ≤ 1) were measured in air in the (1123–1273) K temperature range. The results obtained for YBaCo2O5.0 were fitted using a Maier-Kelley function. The smoothed values of Δ298.15TH∘, Cp(T), and Δ298.15TS∘ were calculated for thermodynamically stable YBaCo2O5.0 in the temperature range 1150 ≤ T, K ≤ 1350. The drop calorimetric results for the metastable YBaCo2O5.33 were used to evaluate the standard enthalpy of its reduction at 298.15 K, ΔHred∘, as (161 ± 15) kJ·(mol O2)-1 (expanded uncertainty with ≈0.95 level of confidence), which is significantly less endothermic than ΔHred∘ of some other double perovskite cobaltites, RBaCo2O6-δ (R – Pr, Gd), within similar oxygen nonstoichiometry ranges (0.5 ≤ δ ≤ 1.0).