The melting mechanism was investigated by considering the role of surfaces with regard to the concentration and migration of vacancies. For many metals, it was found that, while the vacancy concentration in the bulk was about 0.37% at the equilibrium melting point, T0, the vacancy concentration at the free surface could be as high as 10% (similar to that in the bulk at the superheating limit). Melting was believed to be associated with a lattice instability, induced at a critical vacancy concentration of about 10%; both at the surface and within the crystal lattice. The sudden increase in vacancy concentration, from 0.37 to 10%, upon melting at T0 could be explained as being a result of surface melting. The surface pre-melting behaviour of metals was interpreted quantitatively by considering vacancy migration there.

Melting of Metals - Role of Concentration and Migration of Vacancies at Surfaces. Q.S.Mei, K.Lu: Philosophical Magazine Letters, 2008, 88[3], 203-11