Investigation of a New Exsolved Cu-Fe-S Phase in “Abnormal Sphalerite”

Abstract

The typical incongruent melting compound YBa2Cu3O(x) was processed by zone reaction-melting. Zone-melted samples exhibited high transport current carrying capacity, up to 3.75 x 10(4) A cm-2 measured by the DC four-probe method at 77 K and in zero field, and 2.0 x 10(4) A cm-2 (pulsed current) in a 1 T field without loss of superconductivity. XRD indicated the formation of a strong {013} texture component for YBa2Cu3O(x) and the existence of Y2BaCuO5 phase in samples. SEM and TEM observations revealed the highly oriented microstructure of YBa2Cu3O(x) grains, clean grain boundaries, the dispersed particles of Y2BaCuO5 and a variety of twins and dislocations in YBa2Cu3O(x) grains. 80% of zone-melted samples attained J(c) values higher than 10(4) A cm-2. Chemical composition and phase composition indicated crucial influence on the transport current carrying capacity of the zone-melted superconductors. It was estimated that the presence of Y2BaCuO5 in a sample at a concentration of higher than 30% by weight strongly suppressed its supercurrent to a very low value, or even caused it to be non-superconducting. The potential capability of the zone reaction-melting process to achieve still higher current carrying capacity for oxide superconductors is discussed.