STRUCTURAL AND COMPOSITIONAL CHARACTERIZATION OF RUBIDIUM-CONTAINING CRYSTALS OF THE TL-BA-CA-CU-O SUPERCONDUCTORS

Large single crystals of the Tl-Ba-Ca-Cu-O superconductors have been g rown from fluxes including up to 30 mol% Rb of the amount of Tl employ ed. Various phases have been grown with lattice parameters and superco nducting properties similar to crystals grown previously without Rb, t hough the present crystal plates are usually larger and thicker. There is an increased likelihood of syntactic polycrystal growth as Rb cont ent increases. Successive ion milling combined with energy dispersive X-ray analysis, EDAX, has shown that the Rb is uniformly distributed t hroughout the plates that are single phase crystals. Precession photog raphs show sharp diffraction patterns of quality comparable to our Rb- free plates. Magnetically determined Meissner T-c values and transitio n widths are not significantly altered by Rb substitution. Single crys tal X-ray structure refinements have been carried out on several singl e crystals of each of the four principal phases. In addition various c rystal plates have been characterized and studied by transmission elec tron imaging. (C) 1998 Elsevier Science B.V. All rights reserved.