Oxygen nonstoichiometry, mixed valency and mixed conduction in (La,Sr)(Co,Fe)O3−δ

Defect chemistry for a mixed conductor, La0.6Sr0.4Co0.2Fe0.8O3−δ was studied. Samples were treated under controlled oxygen partial pressure, P(O2), conditions at 1273 K [10− 11.1 ≤ P(O2)/atm ≤ 1], and cooled to room temperature. Oxygen nonstoichiometry and valences of transition metal ions for the treated samples were evaluated by iodometry and X-ray absorption spectroscopy, respectively. With decreasing P(O2), preferential reduction of Co3+ to Co2+ was observed, while iron preserved its higher valence above 3 under conditions studied. A dependency of its electrical conductivity on P(O2) was discussed along with a change in concentration of oxygen vacancies and mixed valences.