INTERFACE CONFIGURATIONS DURING THE DIRECTIONAL GROWTH OF SALOL .1. MORPHOLOGY

The facet crystallography and morphological transitions in directionally grown transparent salol is studied. The facet cell morphologies are observed in situ in experiments where the velocity of growth is imposed and also during recalascence in the presence of a strong positive temperature gradient. It is found that the growth interface of salol is bounded by various combinations of (111) planes. The choice of a particular (111) plane is influenced by the root tip undercooling of the interface. At low undercooling values, facet cracking is observed. At a higher undercooling of the interface, the facet tip angle is noted to decrease while retaining the (111) planes which bound the interface. A model is presented for explaining the growth over a wide range of interface undercooling and the associated cracking phenomena. Stress assisted faceted dendrites are also noted during growth within glass cells which are separated by less than 12 microns. The origin of the dendrites and the emergence of the related spacings are discussed.