Oxygen thermodynamics and defect chemistry of nonstoichiometric manganites Ca0.6−уSr0.4LaуMnO3−δ

• Thermodynamic functions of oxygen in Ca0.6–уSr0.4LaуMnO3–δ from pO2−T−δpO2−T−δ diagrams.
• La doping and oxygen content effect on partial thermodynamic functions of oxygen.
• The relations between enthalpy and entropy of oxygen and thermodynamics of defects.

The chemical potential of oxygen ΔμO(δ,y,T) relative to the standard state is calculated from experimental data for equilibrium oxygen content in Ca0.6–уSr0.4LaуMnO3–δ at different values of temperature and oxygen partial pressure in the gaseous phase. The respective values of partial molar enthalpy ΔH¯O(δ,y) and entropy ΔS¯O(δ,y) are derived from the linear plots for ΔμO(δ,y,T) vs  . temperature. Based on the ideal solution approximation, the equations are obtained that show interrelation of ΔH¯O(δ,y) and ΔS¯O(δ,y) with thermodynamic parameters of defect formation reactions and concentration of defects. It is shown that thermal excitation of Mn4+ cations considerably impacts equilibration of defect species in the crystal structure of Ca0.6–уSr0.4LaуMnO3–δ.

The oxygen chemical potential vs. temperature at different values of oxygen nonstoichiometry and the isothermal changes of oxygen content at variations of oxygen partial pressure with isotherm step of 50°С in Ca0.55Sr0.40La0.05MnO3–δ. The partial molar enthalpy of oxygen in Ca0.6–уSr0.4LaуMnO3–δ at 650°С (solid), 800°С (dashed) and 950°С (dash-dotted).Figure optionsDownload as PowerPoint slide