Thermodynamics of oxygen in CaMnO3 − δ

The experimental data for equilibrium oxygen content were used in order to extract increments of partial molar thermodynamic functions of oxygen with changes of oxygen stoichiometry in calcium manganite CaMnO3 − δ. It is shown that along with the oxygen exchange reaction, thermal excitation of Mn4+ cations plays an important role in equilibration of charged manganese species that appear in response to the loss of oxygen at heating. The interrelation of partial molar enthalpy and entropy of oxygen with electron and ion defect formation parameters is obtained in approximation of the point defect model. The nearly linear changes of oxygen partial molar enthalpy are shown to directly reflect thermally driven changes in concentration of Mn3+ cations.