We have conducted a thorough investigation of the high temperature behaviour of crystalline interfaces in 2-dimensional close-packed and 3-dimensional f.c.c. Σ = 7 bicrystals using the atomistic computer simulation technique of molecular dynamics. Gibbs free energies of the bicrystals were computed using the determinant technique and a computer calorimetry technique which we describe. The thermodynamic properties of the boundary were monitored over a wide range of temperatures, up to the bulk melting point. We observed a first order phase transition of the grain boundary in the 2D and 3D bicrystals at temperatures well below the bulk melting temperature. At the transition temperature the crystalline grain boundaries are replaced by highly disordered liquid-like layers.
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