Use of the Rigid Band Formalism to Interpret the Relationship between O Chemical Potential and Electron Concentration in ${\mathrm{La}}_{1-\mathit{x}}{\mathrm{Sr}}_{\mathit{x}}{\mathrm{CoO}}_{3-\mathit{\delta }}$

The equilibrium oxygen chemical potential of mixed oxygen ion and electron conducting perovskites ${\mathrm{La}}_{1-x}{\mathrm{Sr}}_x{\mathrm{CoO}}_{3-\delta }$ was measured as a function of $\delta$ and x by high temperature oxygen coulometric titration. An almost linear decrease in the chemical potential is observed with increasing net electron concentration. The observed behavior is interpreted to reflect the corresponding change in the Fermi level upon gradually filling up states in a broad electron band with electrons induced by vacancy formation and Sr doping. Assuming a rigid band formalism, an apparent density of states at the Fermi level was calculated, the value of which is in good agreement with that obtained from XPS.