Critical currents in melt textured YBa₂Cu₃O_y superconductors

Samples of polycrystalline YBa₂Cu₃O_y superconductor were prepared by melt textured growth (MTG). The melting parameters, including temperature gradient at solidification, melting temperature, melting time and cooling solidification rate, are key factors in preparing textured samples. Scanning electron microscopy (SEM) shows that the sample has a dense, layered structure with regular alignments of plate-shaped crystals. The superconducting transition of the samples was measured using the four point and mutual inductance methods. The zero resistance temperature and onset of diamagnetism of the samples occur at 92 and 91 K, respectively. The critical currents have been measured under magnetic fields from 0 up to 7 T at 77 K using the d.c. four point method. The highest J_c for the best sample in zero field at 77 K was 11 000 A cm^-2. The results for J_c in magnetic fields show that the field dependence of J_c which exists in sintered materials is greatly reduced. This means that the limitations of the weak link problem in sintered materials can be reduced by MTG processing. The anisotropic field dependence of J_c seems to be small for the MTG samples.