Oxygen stoichiometry and expansion behavior of Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3 − δ

Abstract

The oxygen stoichiometry of Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3 − δ (BSCF) was determined by isothermal thermogravimetry between 500 and 1000 °C in combination with a redox titration. The oxygen stoichiometry of BSCF varies from 2.47 at log p O2 = 0 to 2.36 at log p O2 = − 5.6 at 700 °C and from 2.42 at log p O2 = 0 to 2.25 at log p O2 = − 5.6 at 1000 °C, respectively. At T = 500 °C partial decomposition of BSCF is observed. The variation of the oxygen stoichiometry as a function of oxygen partial pressure between 700 ≤ T ≤ 1000 °C is described with a semi-empirical defect model. The thermal expansion of BSCF and the macroscopic chemical expansion were determined for different oxygen stoichiometries by dilatometry in an inert atmosphere. The microscopic chemical expansion, which was derived from the variation of lattice constants of samples synthesized at low oxygen partial pressures, agrees well with the macroscopic chemical expansion. The chemical expansion coefficient of BSCF is smaller compared to the majority of mixed conductors. Moreover, the variation of the thermal expansion coefficient with the oxygen stoichiometry is small.