High-temperature X-ray diffraction study of the peritectic reactions of Bi-2212 with and without Ag additions

Abstract

High-temperature X-ray diffraction (HTXRD) was used to determine the peritectic melting sequence of Bi 2Sr 2CaCu 2O 8 (Bi-2212) and Bi-2212 + 20 wt.% Ag thick films on MgO substrates. The residual carbon concentration of all samples was reduced to 1600 ppm by careful thermal treatment before the HTXRD analyses. Analysis of samples quenched in oil using XRD and EMPA supports the HTXRD results. Lattice-parameter analyses were used to determine the compositions of solid solutions present in the reaction sequence. In the case of pure Bi-2212, two phases form immediately on melting at 870°C, namely (Ca x , Sr 1− x )CuO 2 (1:1) and an unidentified phase. The unidentified phase decomposes by 900°C, while the 1:1 phase is present up to 920°C. (Ca 1.4Sr 0.6)CuO 3 (2:1) forms by 880°C, immediately after the 1:1 phase, and decomposes by 930°C, while (Ca 0.96Sr 0.04)O appears at 900°C, and coexists with the liquid up to at least 1350°C. Only slight changes in the solid-solution compositions were found with 20 wt.% Ag added to the system, with the phases and stability regions remaining the same.