Enhanced critical magnetization currents of hot-pressed YBa₂Cu₃O_6+x through partial melting post-oxygenation

Abstract

Bulk YBa₂Cu₃O_6+x superconductor was synthesized using the hot-pressing technique combined with various oxygen-annealing cycles. Pressed samples, with theirab-planes perpendicular to the pressing axis, annealed in oxygen at the partial melting point of approximately 1000°C and slowly cooled at different rates in the temperature ranges 975–935 and 935–450°C showed enhanced magnetization hysteresis loops with a weak field dependence. Due to oxygen-deficient regions in these materials, anomalous magnetization hysteresis loops with a “butterfly” contour were observed at temperatures above 50 K. This indicates that these regions act as effective flux-pinning centres at high temperatures. The critical magnetization current density (J _c) calculated using the Bean model and the average grain dimension was of the order of 10⁴ A cm⁻² at 75 K up to 1 T. Because of a shorter period of oxygenation and a weak field dependence ofJ _c s, the synthesis process reported here is very promising and further optimization of the period in various annealing temperature ranges to limit the weak links caused by excessive grain growth becomes necessary. The observations are also correlated with the morphology and the crystal orientation studied by scanning electron microscopy and X-ray diffractometry, respectively.