Effect of applied magnetic field on the I–V characteristics of melt-textured YBa 2Cu 3O 7−x superconductors containing grain boundaries

Abstract

The current-voltage ( I–V) characteristics of sintered and melt-textured YBCO superconductors containing grain boundaries have been studied in the presence of applied magnetic fields up to 1.5 T. The melt-textured samples contain grain boundaries of angles up to 16°. The measurements were performed at 77 K using DC transport current. In applied fields, sintered and melt-textured specimens are found to exhibit power-law I– V characteristics. In both cases, the power exponent n is found to decrease with increasing field and the corresponding decrease in J c. In sintered specimens, this behavior is interpreted in terms of network models where the n value is related to the width of the critical current distribution and the overall J c. It is also found that the network models can represent the I– V behavior in melt-textured specimens including those with grain boundaries. However, if these models do not apply to melt-textured specimens, the power-law I– V characteristics can be represented by flux motion models such as collective flux pinning or a vortex-glass transition.