EFFECT OF APPLIED MAGNETIC-FIELD ON THE IV CHARACTERISTICS OF MELT-TEXTURED YBA2CU3O7-X SUPERCONDUCTORS CONTAINING GRAIN-BOUNDARIES

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-degrees. 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.