Cooperativity in the dislocation theory of melting

Abstract

THE interesting behaviour of the shear moduli of alkali halides in the vicinity of the melting transition was recently noted by Tallon, Robinson and Smedley1. These parameters do not fall to zero at the crystal melting temperature, Tm, as proposed by Born2, but a zero value is attained on extrapolating to the dilation corresponding to the liquid at Tm. It is suggested that ‘melting occurs when a solid can transform isothermally to a state of zero shear modulus’, and that a two-phase melting model follows. Although they do not deal with the microscopic processes occurring along the melting isotherm their discussion does have a bearing on the important role of cooperative effects. We comment here both on the specific points raised by their analysis and the question of cooperativity in the dislocation theory of melting.