Microstructural design and processing of cuprate superconductors

Abstract

Many of the anticipated applications utilizing the cuprate superconductors rely on their being able to carry high critical current densities. At the present stage in their development single crystals and thin epitaxial films have been demonstrated to carry in excess of 102A m-2 at 77°K. In marked contrast the best bulk polycrystalline materials have only exhibited transport critical current densities of approximately 10-1 A m-2 in the absence of a magnetic field. More typically, bulk samples of yttrium barium cuprate have transport critical current densities in the range of 10-2A m-2. The much lower values of the polycrystalline materials has been attributed to the presence of grain boundaries that inevitably act as superconducting weak links. Whilst experiments, including ones on individual grain boundaries in bicrystal thin films have confirmed this behavior it is far from clear what the underlying causes are for this poor superconducting coupling across grain boundaries. In this short contribution the authors outlines a number of factors that can be influenced during processing, starting with describing the type of microstructure that might be expected to have the highest transport critical current.