Stabilization of Strontium Analogues of Barium Yttrium Cuprate Perovskites via Chemical Substitution

We report the synthesis and characterization of Sr₂YCu_3-xM_xO_y, M = Al, Pb, Fe, and Co, analogues of the 92 K superconducting perovskite Ba₂YCu₃O₇. While phase-pure Sr₂YCu₃O₇ 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 property/dopant relationships. For Sr₂YCu_3-xM_xO_7+δ, samples with M = Al or Co have δ = 0 for all x and δ > 0 when M = Fe and x ≈ 1. Samples were characterized by resistivity and dc magnetic susceptibility measurements. Superconductivity is observed in samples with low levels of metal substitution; however, the volume fraction is small (<2%) and cannot be uniquely attributed to the perovskite phase. A comparison of solid-state ²⁷Al NMR spectra of Ba- and Sr-based perovskites suggest a different Al environment in these two systems.