STUDY OF ISOSTRUCTURAL PHASES IN 2212-TYPE HIGH-T-C SUPERCONDUCTORS

Single crystals of 2212-type compounds were grown and investigated by x-ray diffraction (XRD) and electron microprobe analysis (EMPA). Sever al isostructural Bi-2212-type phases were indicated, which differed in chemical composition, lattice parameters and physical properties. Sev eral sequences of solid solutions have been distinguished which differ in the Pb amount in the crystals. In each sequence the lattice consta nt c changes successively depending on the concentration of Y or rare earth (RE) substituting for Ca. However, in each sequence only several single-phase samples with particular compositions were found. The com pounds with intermediate compositions, and hence with intermediate Y, RE concentrations, represent an epitaxial intergrowth on the stable ph ases or manifest themselves as inclusions at decomposition of solid so lutions at melt quenching. The cation sublattice was found to be domin ant in the structure formation. Determination of the sequences of soli d solutions allowed us to propose a decantation method to obtain monop hase single crystals. The phase intergrowth scheme was also considered .