Subsolidus Phase Relations of the CoO_x-CuO-SrO System  

The subsolidus phase relations of the CoO_x-CuO-SrO system were investigated in air. The samples were equilibrated at 900 °C. The pseudo-ternary section contains three stoichiometric binary oxide phases (Sr₂CuO₃, SrCuO₂ and Sr₁₄Cu₂₄O_41−δ) and a binary oxide solid solution: Sr_6+xCo₅O_15+δ (0 ≤ x ≤ 0.36). Two binary phases extend into the ternary system forming solid solutions, i.e., Sr₁₄Cu_24−xCo_xO_41−δ (0 ≤ x ≤ 5) and Sr_6+xCo_5−yCu_yO_15+δ (0 ≤ x ≤ 0.36, 0 ≤ y ≤ 1.0). The Sr_6+xCo₅O_15+δ solid solution was found to undergo a phase separation into a mixture of Sr₆Co₅O_15−δ and Sr₁₄Co₁₁O₃₃ upon annealing at 600 °C. This transformation is reversible.