Stabilization of Strontium Analogs of Barium Yttrium Cuprate Perovskites via Chemical Substitution.

We report the synthesis and characterization of Sr sub 2 YCu sub (3-x) M sub x O sub y, M=Al, Pb, Fe, and Co, analogues of the 92K superconducting perovskite, Ba sub 2 YCu sub 3 O sub 7. While phase pure Sr sub 2 YCu sub 3 O sub 7 cannot be prepared, cation substitution for Cu stabilizes this phase. Crystals of these phases were grown from CuO-rich melts containing appropriate melt impurities or from lead oxide-based melts. Ceramic samples were prepared for detailed studies of stability ranges, oxygen content, and for property/dopant relationships. Samples were characterized by resistivity and dc magnetic susceptibility measurements. Samples with relatively low levels of substituted metal superconduct at low temperature. The highest T sub c is obtained for Sr sub c YCu sub (2.7) Fe sub (0.3) O sub 7 with T sub c sup (onset) =60K and R=0 at 10K. For Sr sub 2 YCu sub (3-x) M sub x O sub (7+delta), samples with M=Al or Co have delta=0 for all x and delta>0 when M=Fe and X~1. A comparison of solid state sup (27) Al NMR spectra of Ba and Sr based perovskites suggest a different Al environment in these two systems.