Relation of the N-value of the resistive transition to microstructure and inhomogeneity for YBa2Cu3O7 wires

Measurements are reported of resistive transitions at 77 K for a series of YBa₂Cu₃O₇ wires as a function of applied magnetic field. The transitions are very broad and for electric fields in the range 10^-6 to 10^-3 V m^-1 can be fitted approximately by a power law with n-values in the range 4-60. The n-value is observed to fall with increasing applied magnetic field and shows strong hysteresis related to trapped flux when the field is cycled. The variation of both critical current and n-value with applied field is related to the microstructure of wires with different additives, and on a series of wires of different bulk density prepared using viscous processing techniques. Extensions to the analysis for conventional composites makes it possible to relate the n-value to the statistical critical current distribution