The thermodynamic parameters of oxygen nonstoichiometry defects in lanthanum cobaltite doped with acceptor impurities (Sr and Ni)

Abstract

The oxygen nonstoichiometry δ of lanthanum cobaltite doped with acceptor impurities (Sr and Ni), La1 − xSrxCo0.9Ni0.1O3 − δ (x = 0.1, 0.3), was studied by high-temperature thermogravimetry over the temperature and pressure ranges 723 K ≤ T ≤ 1373 K and 10−3 atm ≤ \(p_{O_2 } \) ≤ 1 atm. The partial replacement of cobalt with nickel and lanthanum with strontium increased the oxygen nonstoichiometry δ. The partial molar enthalpies \(\Delta \bar H^\circ _O \) and entropies \(\Delta \bar S^\circ _O \) of solution of oxygen in the solid phase were calculated. Models of point defect formation were suggested and analyzed. The equilibrium constants of formation and concentrations of predominant point defects, ionized oxygen vacancies Vo.., holes MeCo. (CoCo. and NiCo.), and electrons MeCo′ (CoCo′ and NiCo′) localized on 3d transition metals, were determined by nonlinear regression from the experimental and theoretical logp\(p_{O_2 } \) −δ dependences.