Oxygen Stoichiometry and Chemical Expansion of Ba_0.5Sr_0.5Co_0.8Fe_0.2O₃_-_δ Measured by in Situ Neutron Diffraction

Abstract

The structure, oxygen stoichiometry, and chemical and thermal expansion of Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) between 873 and 1173 K and oxygen partial pressures of 1 × 10-3 to 1 atm were determined by in situ neutron diffraction. BSCF has a cubic perovskite structure, space group Pm3̄m, across the whole T−pO2 region investigated. The material is highly oxygen deficient with a maximum oxygen stoichiometry (3 − δ) of 2.339(12) at 873 K and a pO2 of 1 atm and a minimum of 2.192(15) at 1173 K and a pO2 of 10-3 atm. Good agreement is obtained between oxygen stoichiometry data determined by neutron diffraction and thermogravimetry. In the range covered by the experiments, the thermal and chemical expansion coefficients are 19.0(5)−20.8(6) × 10-6 K-1 and 0.016(2)−0.026(4), respectively.