STRUCTURE MODIFICATION TO INCREASE FLUX PINNING IN Hg-Ba-Ca-Cu-O SUPERCONDUCTORS J. D. Jorgensen, O. Chmaissem, D. N. Argyriou, D. G. Hinks, P. Guptasarma, Materials Science Division and Science and Technology Center for Superconductivity, Argonne National Laboratory, Argonne, IL 60439; J. Shimoyama, K. Kishio, Department of Applied Chemistry, Univ. of Tokyo, Bunkyo-ku, Tokyo 113, Japan; K. Yamaura, Z. Hiroi, M. Takano, Institute for Chemical Research, Kyoto Univ., Uji, Kyoto-Fu 611, Japan; B. G. Storey, H. Zhang, L. D. Marks, Y. Y. Wang, V. P. Dravid, Dept. of Materials Science and Engineering and Science and Technology Center for Superconductivity, Northwestern Univ., Evanston, IL 60208; B. Dabrowski, Physics Dept., Northern Illinois Univ., DeKalb, IL 60115

Chemical substitution of Cr or Re on the Hg site and Sr on the Ba site has been used to enhance the flux pinning of Hg-Ba-Ca-Cu-O superconductors. The structural modifications have been characterized by neutron powder diffraction and electron diffraction and microscopy. Three features of the modified structures are thought to influence the flux pinning. Increased coupling of pancake vortices to form vortex lines can result from either shortening or metallization of the blocking layer. Extended defects that can pin flux can be formed as a result of the substitutional defects. This work suggests that such techniques can be used to increase the usefulness of these materials for bulk current-carrying applications.

This work is supported by the National Science Foundation, Office of Science and Technology Centers, grant No. DMR 91-20000, the US Dept. of Energy, Division of Basic Energy Sciences - Materials Sciences, contract No. W-31-109-ENG-38, and a grant-in-aid for scientific research from the Ministry of Education, Science, and Culture of Japan.