Characteristic spherulitic microstructure in partial-melt-processed YBa2Cu3Ox/HfO2

The microstructure of partial-melt-processed YBa2Cu3Ox/ HfO2 has been studi ed by transmission electron microscopy. A characteristic spherulitic micros tructure is formed in the system. A. model for the growth mechanism has bee n proposed. The critical heterogeneous nucleation of the YBa2Cu3Ox phase ap pears to occur from the melt in an epitaxially controlled manner on CuO par ticles. Subsequent growth of YBa2Cu3Ox platelets from the nucleus region is repeatedly interrupted by the nucleation of hafnium-rich phases in the liq uid at the solid/liquid interface in a manner that again appears to be epit axially controlled and that promotes the splay of the c orientation of the YBaCuO grain.