Modelling the V-I characteristic of coated conductors

The critical current densities of coated conductor samples are limited by the presence of low-angle grain boundaries. These boundaries provide an obstacle to current flow, which is determined by their misorientation angle. The superconducting layer of a coated conductor tape may be considered as a network of grains linked together by grain boundaries through which the supercurrent must pass. Such a network has been investigated using a two-dimensional grain model. The three-dimensional orientations of grains in the superconducting network can be assigned randomly based on information obtained from EBSD and x-ray texture measurements. By assigning critical current values to boundaries based on their calculated misorientation, the overall J(c) of macroscopic modelled samples can then be calculated. This paper demonstrates how such a technique is applied using a small-scale, idealized sample grain structure in an applied magnetic field. The onset of dissipation at the critical current may be viewed in terms of the flow of the magnetic flux across the sample along high-angle grain boundaries when the critical current is first exceeded. Through such a consideration, the model may be further used to predict the current-voltage characteristic of the coated conductor sample around the superconducting transition.