IN-SITU OBSERVATION OF MELTING DISSOLUTION, NUCLEATION AND GROWTH OF NDBA2CU3OX BY HIGH-TEMPERATURE OPTICAL MICROSCOPY/

The pseudo-binary phase diagram between NdBa2Cu3Ox and Ba3Cu10O13, and the nucleation and growth of NdBa2Cu3Ox in air have been observed in situ using high-temperature optical microscopy. It has been observed t hat NdBa2Cu3Ox melts peritectically (NdBa2Cu3Ox --> Nd4Ba2Cu2O10 + L) at 1098 degrees C for the (1/13) Ba3Cu10O13 composition range of 0-60 mol% and forms a high-temperature solution in 60-100 mol% at 922-1098 degrees C. The in situ observations of crystallization of NdBa2Cu3Ox f rom high-temperature solutions reveal that the growth mechanism depend s on the cooling rate. The morphological changes from polyhedral via s tacked to dendritic crystals with increasing supercooling were clearly observed. In contrast, the growth morphology for crystals grown from peritectic melt was independent of the cooling rate, which indicated t hat solute diffusion is the rate-limiting factor. (C) 1998 Elsevier Sc ience B.V. All rights reserved.