DEFECT-INDUCED MELTING AND SOLID-STATE AMORPHIZATION

DESPITE the strong interest in melting over the past 100 years, a general theory for the crystal-liquid transition has not been established 1. Lattice-instability models, which are either vibrational 2, elastic 3, isochoric 4, defective 5 or entropic 6 in nature, all predict a melting point somewhat above the experimentally observed thermodynamic melting temperature, with the ultimate stability limit of a superheated crystal being determined by the equality of crystal and liquid entropies 4,6; this forces regular melting to be a first-order transition. Here I present a model of melting that is driven by the incorporation into the lattice of randomly frozen-in defects. An isentropic condition limits the stability of the crystal as a function of defect concentration; above the glass transition temperature the crystal melts to a liquid, whereas below it 'melting' produces an amorphous solid. This model yields a generic melting diagram with a tunable parameter (defect concentration) that can characterize the static disorder present in solid-state amorphization 7-9, the thermodynamic stability of small clusters 10 and nanocrystalline materials 11, and the frustration present in spin glasses 12 . The model is also relevant to glacial 13, geological 14 and stellar-atmospheric 15 melting processes.