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

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