Oxidation–reduction behavior of La0.8Sr0.2ScyMn1 − yO3 ± δ (y = 0.2, 0.3, 0.4): Defect structure, thermodynamic and electrical properties

Abstract

Oxygen non-stoichiometry of La0.8Sr0.2ScyMn1−yO3±δ (y=0.2, 0.3, 0.4) oxide was studied by coulometric titration as a function of oxygen partial pressure, p(O2), and temperature in a range of 923–1023K. Depending on the Sc doping amount, p(O2), and temperature, oxygen non-stoichiometry varies significantly. Under a reducing condition, La0.8Sr0.2ScyMn1−yO3±δ shows both oxygen excess and oxygen deficient compositions. At the higher p(O2) region, the oxygen excess composition is due to metal ion vacancies, whereas in the lower p(O2) region, the oxygen deficient composition is due to the formation of oxygen vacancies. The experimental data were analyzed by a random defect model. Partial molar enthalpy and partial molar entropy of oxygen vacancy formation are calculated using the Gibbs–Helmholtz equation from the non-stoichiometric data. The electrical conductivity was measured as the function of the oxygen partial pressure and temperature. In the lower p(O2) region, electrical conductivity strongly depends on the oxygen non-stoichiometry.