Grain-boundary melting transition in a two-dimensional lattice-gas model

Abstract

A two-dimensional lattice-gas model that is capable of producing gas, liquid, and two orientations of a solid phase is adopted to study properties of a boundary between two crystalline grains by use of a nine-site cluster approximation of the cluster-variation method. At a temperature far below the melting temperature $T_m$, a gradual but well-defined transition is discovered between the low- and high-temperature structures of the boundary; this transition signals the onset of a liquidlike phase inside the boundary. The thickness of the boundary increases with $T$; the excess entropy due to the boundary diverges as $-\ln (T_m-T)$ near $T_m$; and the grain boundary is completely wet with liquid at $T_m$.