Defect chemistry and high-temperature thermodynamics of PrBaCo2O6-δ

Abstract

Using the drop calorimetry and differential scanning calorimetry (DSC), the enthalpy increments of pure PrBaCo2O6-δ double perovskite in air in the temperature range from 365.3 K to 1272.8 K were obtained. As-measured enthalpy increments corresponded to the constant pO2, but variable oxygen content in PrBaCo2O6-δ (isodynamical conditions). The defect structure analysis yielded the analytical expressions for the equilibrium oxygen partial pressure, log(pO2) = f(δ, T), and the partial molar enthalpy of oxygen, Δh¯O = f(T, δ) in PrBaCo2O6-δ, both functions being valid in relatively wide temperature range. The value of Δh¯O at 1273 K was assessed independently by means of direct oxidation of PrBaCo2O6-δ in the DSC setup, and was found to agree well with Δh¯O calculated from the defect structure model and pO2 – T – δ diagram. The knowledge of Δh¯O = f(T, δ) allowed recalculating the enthalpy increments for the sample with constant oxygen content, Δ298.15TH∘(PrBaCo2O5.77), which were fitted with a modified Einstein function. The smoothed values of Δ298.15TH∘, heat capacity Cp(T), and entropy increments Δ298.15TS∘ were evaluated and tabulated for PrBaCo2O5.77 in the temperature range 350 ≤ T/K ≤ 1300. The results obtained can be used for calculating Δ298.15TH∘, Cp(T), and Δ298.15TS∘ for PrBaCo2O6-δ with an arbitrary constant oxygen content.