YBa₂Cu₃O_7−x superconductive tapes and wires: a peritectic sintering procedure to improve the quality

Abstract

YBa₂Cu₃O_7−x tapes were made by a powder-in-binder technique, using polysulphone (PSF) as the organic polymer andN-methyl-2-pyrrolidone (NMP) as the solvent. The suspension is cast onto a glass substrate plate to form the tape (Doctor Blade method) and is consequently immersed into a non-solvent to remove the solvent by phase inversion. In this paper we describe the different steps in an improved “peritectic” thermal treatment that are necessary to make the green product into a superconductive tape. Three steps are important in this heat treatment. First the polysulphone binder has to be removed as much as possible without reacting with the YBa₂Cu₃O_7−x material. Next the sample has to be sintered into a dense ceramic material. In order to improve the intergranular connections, the sample is partially melted at relative low temperature in vacuum. The sample is subsequently heated up in oxygen to the normal sinter temperature. At this high temperature the YBa₂Cu₃O_7−x phase will be restored by a peritectic reaction of the Y₂BaCuO₅ with a liquid phase. The final step is a two step anneal to ensure the full oxidation of the superconductor.