HIGH-TEMPERATURE X-RAY-DIFFRACTION STUDY OF THE PERITECTIC REACTIONS OF BI-2212 WITH AND WITHOUT AG ADDITIONS

High-temperature X-ray diffraction (HTXRD) was used to determine the p eritectic melting sequence of Bi2Sr2CaCu2O8 (Bi-2212) and Bi-2212 + 20 wt.% Ag thick films on MgO substrates. The residual carbon concentrat ion of all samples was reduced to 1600 ppm by careful thermal treatmen t before the HTXRD analyses. Analysis of samples quenched in oil using XRD and EMPA supports the HTXRD results. Lattice-parameter analyses w ere used to determine the compositions of solid solutions present in t he reaction sequence. In the case of pure Bi-2212, two phases form imm ediately on melting at 870 degrees C, namely (Ca-x, Sr-1-x)CuO2 (1:1) and an unidentified phase. The unidentified phase decomposes by 900 de grees C, while the 1:1 phase is present up to 920 degrees C. (Ca1.4Sr0 .6)CuO3 (2:1) forms by 880 degrees C, immediately after the 1:1 phase, and decomposes by 930 degrees C, while (Ca0.96Sr0.04)O appears at 900 degrees C, and coexists with the liquid up to at least 1350 degrees C . Only slight changes in the solid-solution compositions were found wi th 20 wt.% Ag added to the system, with the phases and stability regio ns remaining the same.