Increasing the critical current density of BSCCO/Ag superconducting microcomposites by mechanical deformation

Abstract

Mechanical deformation and annealing have been used to produce BSCCO/Ag superconducting microcomposites with a textured microstructure and improved critical current density, J c. Melt spun precursor ribbons, before or after oxidation and annealing, were covered with metal sheets, and then subjected to various combinations of mechanical deformation and annealing. Superconducting ribbons with T R=0 =104-110 K and J c(77) as high as 4000 A/cm 2 have been produced with this method. Research has concentrated on the interrelations of processing, microstructure and superconducting properties. Results indicate that the deformation processing, the oxidation and annealing conditions, the sequence of deformation, oxidation and annealing, the alloy composition and the nature of the cover sheets are the most important factors that influence superconducting properties. Because a well-textured “2223” microstructure can only be achieved by deformation of a specimen with well-developed “223” phase, an annealing at suitable temperature was needed before deformation. While the deformation caused microcracking and separation of the “2223” grains, a short-time reannealing was necessary to recover J c after each deformation step. Silver in the microcomposites is believed to be beneficial as it aided in the deformation and texturing processes, and restrained the re-growth of the “2223” grains during re-annealing. The Lotgering factor, F, was measured via X-ray diffraction to determine the degree of texture in the 2223 phase. It has been observed that the F factor increased with the extent of deformation, and the J c increased with the F factor. The effect of the cover sheets and the possibility of using different metals inluding the base metals Ni, Cu and stainless steels as the cover sheets is discussed in terms of processing, adhession and reaction.