Preparation of High-Tc Superconducting Thick Films by a Low-Pressure Plasma Spraying

Abstract

Superconducting thick films of YBaCuO systems have been prepared by a low pressure plasma spraying technique. After the post-annealing in oxygen at 900~970°C, YBaCuO films showed zero resistance temperatures, T_c of ~90K. In order to improve the critical current density, J_c of the films, a melt-reaction method has been newly developed. A flux layer richer in Ba and Cu was coated on a YBa₂Cu₃O_x+Y₂BaCuO_x mixure layer by a low pressure plasma spraying, and then the double-layered film was annealed at 930–970°C, where the flux layer melted. The molten oxide acted as a flux and enhanced grain growth of YBa₂Cu₃O_x. The excess flux reacted with Y₂BaCuO_x and was fully converted to YBa₂Cu₃O_x. The grain growth of YBa₂Cu₃Ox and the reaction between the flux and Y₂BaCuO_x yielded a dense and uniform YBa₂Cu₃O_x layer, so that the J_c of the films were improved up to 2000A/cm². This might be due to the dense structure which improves the coupling between the grains of the superconducting phase, and the grain growth which ruduces the grain boundary.