Premelting

Abstract

Although not quite as complex as the phenomenon of melting, premelting nevertheless provides a major experimental and theoretical challenge. Whether or not the extensive ionic disorder associated with premelting is observed in ionic solids depends on detailed properties of thermally-induced ionic defects and hence on crystal structure. Some consideration is given in this article to properties of ionic defects. A well defined specific-heat peak precedes melting in CaF₂ and other materials with the fluorite structure and considerable effort has been devoted in recent years to this premelting phenomenon. The techniques of neutron scattering and of molecular dynamics simulations have been profitably applied to the problem. Progress is reviewed and the discussion is extended to include silver halides and rare-gas solids. The article concludes with some comments on premelting associated with surfaces of solids and with monolayers of gases adsorbed on surfaces.