Abstract
Practical applications of bulk polycrystalline YBCO superconductor have been severely limited, due to the weak link behavior of grain boundaries, caused by the presence of secondary phases and microcracks at the boundary interface. Partial removal of liquid phase during melt texturing has demonstrated a potential to enhance the grain boundary coupling significantly, thus improving the transport current carrying properties of bulk polycrystalline YBCO superconductors. In this paper, the effects of processing conditions during melt texturing, namely, the hold time above the peritectic temperature and the subsequent cooling rate, on microstructure and current-voltage characteristics have been investigated. Larger hold times (> 0.5 h) along with higher cooling rates (> 1.5°C/h) are found to increase the precipitation of unreacted liquid along the grain boundaries and yield poor current transport characteristics. Higher cooling rates also increase the number of cracks at the grain boundary. Very slow cooling rates (0.5°C/h), however, increase the processing time and the distortion of sample geometry. Moderate dwell times of 0.3 h and slow cooling rates of 1.0°C/h yield the optimum I–V characteristics. These characteristics are explained using a recently developed dissipative model by Kunchur et al.
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