ABO₃(A=La, Sr, B=Fe, Co, Ni, Cu, Mn, Ti) perovskites are of great interest due to their mixed electronic and oxygen ion conductivity. They are candidates for the electrodes of SOFCs. The mixed conductivity can be enhanced through the substitution of La³⁺ by Sr²⁺ at A sites, and the substitution of Fe³⁺ by other transition metal ions at B sites. The charge imbalance and overall charge neutrality can be maintained by the presence of charged oxygen vacancies and mixed valence state ions at the B sites. These point defects are the origin of the mixed electronic and oxygen ion conductivity. This study investigates the effects of substitutions at A sites and/or B sites on the crystal and magnetic structure, oxygen vacancies, and the thermal expansion coefficients at different temperatures and gaseous environment. The oxygen vacancy concentration can relax the perovskite distortion and has a close relationship with the magnetic properties. La_0.6Sr_0.4FeO_3-δ, La_0.6Sr_0.4Fe_0.8Co_0.2O_3-δ , and La_0.8Sr_0.2Fe_0.8Co_0.2O _3-δ can be good candidates for the cathodes of SOFCs at intermediate temperature.

The double perovskite Ba₂YRu_0.85Cu_0.15O ₆ superconductor and a mixture of 5wt% YBa₂Cu₃O 7-δ and undoped Ba2YRuO6 were investigated with the aid of neutron diffraction. The 1:1 B site ordering is observed and long range antiferromagnetic ordering of the Ru sublattice with a type I magnetic structure appears when the temperature is below 38K. An incommensurate antiferromagnetic ordering of Cu is observed in the temperature range 38K-85K. This ordering is not seen in undoped material. The decomposition of Cu-doped Ba2YRuO6 into undoped Ba 2YRuO6 and YBa2Cu3O7-δ is not seen. YBa₂Cu₃O_7-δ is not stable at the temperature used to prepare the Cu-doped Ba₂YRuO₆ superconductor. These results confirm the presence of superconductivity without CuO₂ planes.