EFFECT OF HIGH-TEMPERATURE HEAT-TREATMENT ON THE PINNING PROPERTIES OF MELT-TEXTURED ND123

We have investigated the effect of high-temperature annealing on the s uperconducting transition and the flux pinning properties of Nd123 mel t-textured in 1% O-2-Ar. After the high-temperature annealing, a decre ase in J(c) was observed in most samples even though no appreciable ch ange was observed in T-c. TEM observations and EDX analysis show that the spatial variation of the Nd/Ba ratio almost disappears after high- temperature annealing. Therefore, the observed change in J(c)-B proper ties can be understood by a reduction in the field-induced pinning due to homogenization of Nd/Ba substitution regions. These results strong ly support the idea that the secondary peak effect and high pinning pe rformance in Nd123 can be ascribed to the presence of Nd/Ba spatial va riation. (C) 1997 Elsevier Science B.V.