On the interpretation of voltage versus current data for high- temperature superconductors in terms of distribution of intergrain critical current densities

Abstract

We report on a method for predicting the DC voltage versus current characteristics of thin polycrystalline high-temperature superconductor samples from critical density ( J c) distributions determined from AC susceptibility measurements. A sample may be modeled as a two-dimensional electric circuit with the grain-boundaries (the resistors) assuming a wide range of critical current densities, which are assumed proportional to the boundaries' conductances ( C). The equivalent resistance ( R eq) of a square- lattice network of boundaries may thus be exactly calculated for any number of boundaries by iteratively applying the “delta-Y” transformation to the cells of the network. The J cs for the boundaries may be generated by Monte Carlo techniques following a given statistical distribution, yielding R eq and thus V= IR eq. Changes of microstructure may be simulated by imposing that certain resistors have infinite conductance.