High-Pressure Synthesis of Mo-Containing 1212 and 1222 Compounds, (Cu, Mo)Sr₂YCu₂Oz and (Cu, Mo)Sr₂(Y, Ce)₂Cu₂Oz

A new “1222” compound (Cu, Mo)Sr 2 (Y, Ce) 2 Cu 2 O z is prepared at ambient pressure. After treatment under high oxygen pressure, the sample exhibits a sharp superconducting diamagnetic signal below the critical temperature ( T c ) which varies depending on oxygen pressure. The highest value of T c is 50 K. It is 22 K lower than the maximum T c for the 1212 phase, (Cu, Mo)Sr 2 YCu 2 O z . The fluorite-type slab in the crystal structure is unfavorable for superconductivity in comparison with the Y layer. The T c for the 1222 phase is not enhanced by the partial replacement of Sr by Ba, although approximately 25% of Sr can be replaced by Ba.