Effects of shock-induced defects and subsequent heat treatment on flux pinning in melt-textured YBa 2Cu 3O 7−δ

Abstract

Shock compression of melt-textured YBa 2Cu 3O 7−δ (Y123) results in a nearly uniform defect density which is two to three orders of magnitude higher than unshocked melt-textured material. The crystallographic alignment of the sample relative to the shock wave is critical because slip is limited to the basal plane in Y123. In the experiments the specimens were cut so that their effective c-axis was about 30° from the shock direction. Specimens were recovered intact from high shock pressures. The superconducting order parameter is decreased in the as-shocked state due to disorder of the crystalline lattice, predominantly of the Cu-O chains. A 450°C anneal in oxygen decreases the random atomic disorder, while retaining a large defect density. The defects remaining after a 450°C anneal enhance the intragranular critical current density by a factor of two to three over the unshocked initial value, depending on temperature and applied magnetic field. This shock process could be scaled to larger sizes using chemical explosives. These results show that shock-induced defects enhance J c's in oxygen-annealed melt-textured Y123. The maximum enhancement is expected to occur for shock pressures of about 5 GPa. Determinations of how the degree of mosaic spread and the size and distribution of Y 2BaCuO 5 affect the distribution of defects remain to be investigated.