PHASE-RELATIONS IN THE BI(PB)-SR-CA(Y, RE)-CU-O SYSTEM

Electron microscopy and XRD data for the Bi(Pb)-Sr-Ca-Cu-O system show that in the field under consideration at least two phases of the same (2212) structure, but with different lattice parameters, are crystallizing. The Pb distribution coefficient k has been determined from the Pb concentration in the melt. According to XRD the samples represent epitaxial intergrowth of three phases: one of the (2201) structure, and two of the (2212) structure with slightly different c parameters. In the Bi-Sr-Ca(Y, RE)-Cu-O system the final aggregate represents an intergrowth of three phases: the (2201) phase containing no Y(RE) and two (2212) phases with different c parameters. The fraction of (2201) phase is dependent on the temperature regime. The ratio between the amounts of the (2212) phase is linear with concentration of Y(RE) in the initial melt. The distribution coefficient for Y(RE) depends on the Y(RE) concentration in melt. T(c) correlates with the fraction of the (2212) phase of smaller c parameter, and the fraction that forms depends on the Y(RE) concentration in the melt. Thus, different superconducting properties of the (2212) phases are clearly evident. Electron diffraction pattern analysis has shown that in multiphase products there are components with tetragonal and orthorhombic symmetry; these have different Pb concentrations. It is reasonable to assume that an increase in the amount Y(RE) in the melt causes stabilization of the 2212 tetragonal modification. The orthorhombic distortion is more probable for RE ions with smaller radius.