© North-Holland Publishing Company INTERFACE STRUCTURE AND CRYSTAL GROWTH FROM THE MELT- A MODEL THEORY

A simplified atomic model is developed which displays the essential characteristics ofa two-phase system, one of the phases being highly disordered (quasi-liquid) and the other nearly completely ordered (crystalline). This model is applied to discuss the equilibrium structure of the interface between the two phases and it is shown that this inter-face will either be sharp or diffuse depending on the entropy of fusion and on the coherence length for cooperative structural effects in the liquid. The interfacial free energy is typically in the range 2 to 10 times kTm per surface atom, where Tm is the melting temperature, and is contributed largely by entropy loss in liquid layers near the interface. Finally the model is applied to the crystallization of the liquid, and the concentration of defects quenched into the crystal is calculated as a function of crystallization velocity. 1. Introduction exhibit the same general behaviour. The model, it is hoped, is sufficiently simple and explicit that both In a recent paper [11,to be referred to as I, the its assumptions and their implications are clear. present author proposed a new approach to the dis-cussion of interface structure and crystal growt