Oxygen Stoichiometry and Chemical Expansion of Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3 - δ Measured by in Situ Neutron Diffraction

The structure, oxygen stoichiometry, and chemical and thermal expansion of Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3 - 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 Pm 3̄ m, across the whole T − p O 2 region investigated. The material is highly oxygen deficient with a maximum oxygen stoichiometry (3 − δ) of 2.339(12) at 873 K and a p O 2 of 1 atm and a minimum of 2.192(15) at 1173 K and a p O 2 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.