CONTROLLED GROWTH OF SINGLE-GRAIN YBA2CU3O7 BY TOP-SEEDING MELT-TEXTURING

A Top-seeding-melt-texturing (TSMT) process is investigated by quenchi ng, in order to understand the growth mechanism better. A SmBa2Cu3O7 m elt-processed crystal has been used as a seed crystal for growing a la rge single-grain YBa2Cu3O7 (Y-123) pellet in a Y-123/Y-211 composite w ith PtO2-addition. It was found that the growth is three-dimensional w ith a growth ratio R-100/R-001 close to 1. By comparing the seeded and un-seeded pellets, quenched at different temperatures during growth s tage, their difference in nucleation temperatures were identified. Thi s causes the appearance of a temperature window in which the growth of a large single-grain monolith can be realized. Finally, the growth fr ont morphology was observed and the growth mechanism is discussed in t erms of a highly supersaturated melt by the dissolution of Y-211 parti cles. (C) 1997 Elsevier Science B.V.