ORIGIN OF SUBGRAIN FORMATION IN MELT-GROWN Y-BA-CU-O BULKS

We have studied the origin of subgrain formation in a melt-grown Y-Ba- Cu-O bulk, Microstructural observations suggest that the subgrains are associated with the dislocation walls formed by the amalgamation of d islocations which are created at the growth front when Y2BaCuO5 (Y211) particles are incorporated into the YBa2Cu3Oy (Y123) matrix. The pres ence of subgrain-free regions near the growth sector boundaries shows that the subgrain structure is not formed with cellular growth. We sup pose that the subgrain-free regions were formed during an incubation p eriod of the growth, in which the dislocation density at the growth fr ont is not high enough to assemble dislocation walls. (C) 1998 Elsevie r Science B.V.