Aluminun substitution in Ba sub 2 YCu sub 3 O sub 7.

We have investigated the effect of aluminum incorporation on the structure and superconducting transition of single crystals of high T sub c cuprate perovskite superconductors. The use of alumina crucibles for crystal growth results in incorporation of aluminum to varying extents in crystals of composition, Ba sub 2 YCu sub (3-x)Al sub x O sub 7, x=0-0.22. We have performed x-ray studies on several crystals to determine structural effects of Al incorporation. We find that aluminum substitutes only for copper atoms in the chains. Superconducting transition temperatures, T sub c, determined by dc diamagnetic susceptibility measurements, change only slightly, to ~80K for x=0.1, then drop sharply with higher aluminum concentrations. Results are discussed n relation to the importance of the Cu-O chains and oxygen stoichiometry to superconductivity in Ba sub 2 YCu sub 3 O sub 7.