Improved superconducting properties of melt-textured Nd123 by additional heat treatment

We have investigated the effect of additional heat-treatment on the superconducting transition and the flux pinning properties of Nd-Ba-Cu-O melt-textured in air. After the heat-treatment at high temperatures, > 900 degrees C, under low oxygen partial pressure, P(O-2) = 0.001 atm, the superconducting transition became sharper accompanied by an increase of J(c). However, the increase of J(c) was very small and the secondary peak effect commonly observed in Nd-Ba-Cu-O melt textured in low P(O-2) could not be observed. Transmission electron microscopic observations and energy dispersive X-ray analyses show that the spatial variation of the Nd/Ba ratio is reduced after high-temperature heat-treatment, which indicates that an improvement in T-c and J(c) is attributed to a suppression of Nd substitution on the Ba site. (C) 1997 Elsevier Science B.V.