Oxygen stoichiometry and chemical expansion of Ba0.5Sr0.5Co0.8Fe0.2O3-δ measured by in situ neutron diffraction

The structure, oxygen stoichiometry, and chemical and thermal expansion of Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF) between 873 and 1173 K and oxygen partial pressures of 1 x 10(-3) to 1 atm were determined by in situ neutron diffraction. BSCF has a cubic perovskite structure, space group Pm3m, across the whole T-pO(2) region investigated. The material is highly oxygen deficient. with a maximum oxygen stoichiometry (3 - delta) of 2.339(12) at 873 K and a pO(2) of 1 atm and a minimum of 2.192(15) at 1173 K and a pO(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) x 10(-6) K-1 and 0.016(2)-0.026(4), respectively.