Effect of Ag on Microstructure and Superconducting Properties of Bi2Sr2CaCu2Ox
Transport critical current density Jc of polycrystalline high-Tc oxide superconductors are usually small due to the weak couling of grains. For the Bi-based oxide superconductors, grain coupling is significantly improved by the c-axis grain alignment and high transport Jc was obtained. Especially, for the Bi2Sr2CaCu2OX(Bi-2212), high degree of grain alignment is obtained by the slow cooling and solidification from the partially molten state on Ag substrate.1 By this grain alignment, excellent transport Jc values over 105A/cm2 are attained at 4.2K even in high magnetic fields above 25T. In this solidification process, Ag substrate plays very important roles in the alignment of plate-like Bi-2212 grains.2 During the heat treatment, Bi-2212 decomposes into partially molten state consisting of Bi-free phase, Cu-free phase and liquid phase.3 Ag enhances this decomposition of Bi-2212, and also lowers solidification temperature of Bi-2212 during slow cooling process.4 However, the effect of Ag on the microstructural changes during heating and cooling process is not well investigated yet. Such an investigation is important for the understanding of role of Ag on grain alignment.
KeywordsOxide Layer Molten State Oxide Superconductor Composite Tape Transport Critical Current Density
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