Thermodynamic properties of nonstoichiometric oxygen in manganite Ca0.9Pr0.1MnO3–δ

Resumo

The chemical potential of oxygen Δμ_O relative to its standard state in the gas phase was calculated from the experimental dependences of the oxygen content in various polymorphic modifications of Ca_0.9Pr_0.1MnO_3–δ on the partial pressure and temperature. The partial molar enthalpy \(\Delta {\overline H _O}\) and entropy \(\Delta {\overline S _O}\) of oxygen were obtained from the linear temperature dependences of Δμ_O. Based on the ideal solution approximation, \(\Delta {\overline H _O}\) and \(\Delta {\overline S _O}\) were correlated with the enthalpies and entropies of the defect formation reactions, the concentrations of manganese cations, and the oxygen nonstoichiometry. The thermal excitation of Mn⁴⁺ cations was shown to substantially affect the thermodynamic functions of oxygen.