Phase relations in the systems SrO-Y₂O₃-CuO-O₂ and CaO-Y₂O₃-CuO-O₂ at 1173 K

Abstract

Phase relations in the systems SrO-Y₂O₃-CuO-O₂ and CaO-Y₂O₃-CuO-O₂ at 1173 K were estab-lished by equilibrating different compositions in flowing oxygen gas at a pressure of 1.01 × 10⁵ Pa. The quenched samples were examined by optical microscopy, X-ray diffraction (XRD), energy dis-persive analysis of X-rays (EDAX), and electron spin resonance (ESR). In the system SrO-Y₂O₃-CuO-O₂, except for the limited substitution of Y₃₊ for Sr₂₊ ions in the ternary oxide Sr₁₄ Cu₂₄O₄₁, no new quaternary phase was found to be stable. The compositions corresponding to the solid solution Sr₁₄-xYxCu₂₄O₄₁ and the compound SrCuO_2+δ lie above the plane containing SrO, Y2O3, and CuO, displaced towards the oxygen apex. However, in the system CaO-Y₂O₃-CuO-O₂ at 1173 K, all the condensed phases lie on the plane containing CaO, Y₂O₃, and CuO, and a new quaternary oxide YCa₂Cu₃O_6.5 is present. The quaternary phase has a composition that lies at the center of the non-stoichiometric field of the analogous phase YBa₂Cu₃O_7-δ in the BaO-Y₂O₃-CuO-O₂ system. The com-pound YCa₂Cu₃O_6.5 has the tetragonal structure and does not become superconducting at low temperature. Surprisingly, phase relations in the three systems CaO-Y₂O₃-CuO-O₂, SrO-Y₂O₃-CuO-O₂, and BaO-Y₂O₃-CuO-O₂ are found to be quite different.