The Effect of Metal Substitution on the Upper Critical Field of Ba sub 2 YCu sub 3 O sub 7

Deliberately introducing impurities to systematically alter materials can lead to insights into the chemistry and physics of the high T sub c superconducting oxides. Single crystals have been studied because these are free of intergrain effects and because we can deconvolute the anisotropy effects. We have examined the effect of aluminum substitution on the upper critical field of Ba sub 2 YCu sub 3 O sub 7. The structural consequences of aluminum incorporation are well understood and the critical field is an intrinsic parameter which can be interpreted directly and which serves as a sensitive probe of the superconducting state.