IMPROVED SUPERCONDUCTING PROPERTIES OF MELT-TEXTURED ND123 BY ADDITIONAL HEAT-TREATMENT

We have investigated the effect of additional heat-treatment on the su perconducting 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 incr ease of J(c). However, the increase of J(c) was very small and the sec ondary peak effect commonly observed in Nd-Ba-Cu-O melt textured in lo w P(O-2) could not be observed. Transmission electron microscopic obse rvations and energy dispersive X-ray analyses show that the spatial va riation of the Nd/Ba ratio is reduced after high-temperature heat-trea tment, which indicates that an improvement in T-c and J(c) is attribut ed to a suppression of Nd substitution on the Ba site. (C) 1997 Elsevi er Science B.V.