Importance of electronic band structure to nonstoichiometric behaviour of La_0.8Sr_0.2CoO_{3 − δ}

The partial energy and entropy involved in the process of oxygen incorporation into the mixed oxygen ion and electronic conducting La0.8Sr0.2CoO3 was measured by oxygen coulometric titration. The partial entropy can be assigned to the configurational entropy of randomly distributed oxygen vacancies. The partial energy decreases linearly with increasing oxygen nonstoichiometry. These observations can be explained assuming that electrons, created during vacancy formation, gradually fill electron states in a wide band resulting in a corresponding increase of the Fermi level.