Abstract

The new compound Ba₂InCoO_{5 + δ}, which has a cubic perovskite structure (a = 4.1587(3) Å) at high temperatures, was prepared by heating mixtures of BaCO₃, In₂O₃ and Co₃O₄ in air at 1150 °C for 20 h. Heat treatment of Ba₂InCoO_{5 + δ} in air at 850 °C for 72 h revealed a phase transformation into a brownmillerite-type structure. To stabilize a cubic perovskite phase at moderate temperatures, the solid solutions Ba₂In_{1 − x}Co_{1 + x}O_{5 + δ}, 0 ≤ x ≤ 0.7 and Ba_{2 − x}La_xCoInO_{5 + δ}, 0 ≤ x ≤ 0.8 were prepared. X-Ray diffraction revealed that the cubic perovskite structure is stable only for Ba₂In_{1 − x}Co_{1 + x}O_{5 + δ}, 0.4 ≤ x ≤ 0.6 and Ba_1.2La_0.8CoInO_{5 + δ}, Ba_1.4La_0.6CoInO_{5 + δ} upon heat treatment in air at 850 °C for 72 h.