Enhanced high-field transport critical current density of superconducting bulk Y-Ba-Cu-O prepared by rapid solidification and directional annealing

Abstract

Strongly textured high-Tc bulk Y-Ba-Cu-O was prepared with rapid solidification and directional annealing processes. Sintered YBa2Cu3O7 (1:2:3) samples, produced by conventional ceramic synthesis, were rapidly quenched with a twin rolling mill and directionally annealed by moving the sample at a speed of 0.2 cm/h through a temperature gradient of up to 60 °C/cm from 1020 to 900 °C. We have measured transport Jc of 2000 A/cm2 by pulse current and 1150 A/cm2 by dc at 77 K in a field of 15 T. It has been found that the Jc values measured by pulse and dc methods are approximately equal in high magnetic fields (8–15 T) and Jc measured by pulse current is larger than that measured by dc in magnetic fields below 8 T. The measured values of Jc decrease monotonically with increasing external magnetic field. Scanning and transmission-electron-microscopy studies showed that the 1:2:3 crystallites grow with their c axes perpendicular to the sample traveling direction. Crystallites of ∼2–4 μm of Y2BaCuO5 (2:1:1) phase were observed also with their c axes perpendicular to the sample traveling direction. Grains with twin crystals orientated at ∼90° from each other were observed. Precipitates of CuO were observed using energy-dispersive x-ray analysis. Dislocations with a density of ∼5×109/cm2 were found in the 1:2:3 crystals. These dislocations lie on the a-b plane. The enhancement of Jc probably is due to flux pinning by the dislocations and to the preferred orientation of the crystallites with the a-b plane parallel to the sample traveling direction.

Source-reported materials — not catalogue approval

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