Influence of Composition on Properties of Partially-Substituted Ba sub 2 LnCu sub 3 O sub 7

It is widely known that the superconducting transition temperature of Ba sub 2 YCu sub 3 O sub 7 is degraded only slightly by many substitutions: complete lanthanide substitution on the Y site has been extensively investigated and effects of some partial substitutions (both isovalent and aliovalent) on all three metal sites have been reported. We have found that properties other than T sub c, such as J sub c (T,H) and H sub (c2) (T) can be significantly enhanced by judicious choice of substitutions. This talk will describe the results of electrical, magnetic and structural characterization of a variety of pseudoquaternary alloys of Ba sub 2 LnCu sub 3 O sub 7.