NEW PHASES WITH INCOMMENSURATE-TYPE STRUCTURE IN RE-BA, SR, CA-CU-O AND BI, PB-SR-CA, RE-CU-O SYSTEMS

The single crystal habit and structure of new incommensurate-type phas es in the system [A(2)Cu(2)O(3)](m)[CuO2](n) (where A is alkaline eart h and trivalent metals) were analyzed. Needle-and platelet-like crysta ls were grown from the melt by slow-cooling or decantation. Three modi fications of the phases with m/n values equal to 5/7, 7/10 and 9/13 we re distinguished. The distortion of the second structural fragment, th e plane of Cu-O ribbons, was determined to be significantly larger tha n for the first fragment composed of a ladder between two A-cation lay ers. Superconducting crystals (T-c = 80-85 K) were attributed to the m odification with m = 5 and n = 7. (C) 1998 Published by Elsevier Scien ce B.V. All rights reserved.