Study on the growth mechanism of Bi-2212 ribbon-like thin films on flat Ag substrate by the atomization technique
The growth mechanism of Bi-2212 ribbon-like thin films on flat Ag substrate using an atomization technique was studied. The fine Bi-2212 powders were dispersed on the Ag substrate before the melting process, so as to avoid the change in the composition of the molten phase with distance, which would result in the formation of the impurity phases. Nearly reversible peritectic reaction on cooling causes the formation of well-defined Bi-2212 phase. Based on the results of in situ high temperature microscope observation, the wetting of the molten phase to the growing ribbons was identified as the essential condition for the growth of the ribbon-like thin films.
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 Bi2Sr2CaCu2O8 (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 (Cax, Sr1−x)CuO2 (1:1) and an unidentified phase. The unidentified phase decomposes by 900°C, while the 1:1 phase is present up to 920°C. (Ca1.4Sr0.6)CuO3 (2:1) forms by 880°C, immediately after the 1:1 phase, and decomposes by 930°C, while (Ca0.96Sr0.04)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.
Synthesis of Bi-2212 ribbon-like thin films on flat Ag substrates
Abstract Using (Bi,Pb)-2223 pellets, with nominal composition of Bi 1.8 Pb 0.34 Sr 1.9 Ca 2 Cu 3 O 8+ δ , as starting materials, nearly phase-pure and highly c -axis oriented Bi-2212 ribbon-like thin films were synthesized on flat Ag thin films with tens nm order of root-mean-square surface roughness. The melting growth processes of Bi-2212 ribbon-like thin films were studied by in situ high-temperature microscope observations. A thin liquid layer spread mechanism of the growth of ribbon-like thin films was revealed. The addition of Pb to the starting materials increases the wettability of melting phase on the Ag thin films surface and facilitates the growth of Bi-2212 ribbon-like thin films. Excess Ca and Cu in starting materials sufficiently suppress the formation of Bi-2201 phase in the ribbon-like thin films.