Abstract
A localization criterion for the crystal-liquid phase transition (PT) is suggested, according to which the PT starts when the ratio E d/k B T reaches a boundary value E d(s)/k B T m, above which a solid phase, and below which, a liquid phase is located in the phase diagram. Here, E d is the energy of the delocalization of an atom, k B is the Boltzmann constant, T is the temperature, and E d(s) is the energy of delocalization for the solid phase at the melting point T m. It is shown that this criterion extends the Lindemann criterion of melting to the case of crystallization, and the Loven criterion of crystallization to the case of melting. It is shown that the localization criterion suggested is applicable both for the normally melting substances and for the substances melting with a decrease in the specific volume upon the transition into the liquid phase. The connection of the localization criterion with the vacancy and diffusional criteria of the crystal-liquid PT has been studied. The inequality T s < T m, where T s is the temperature of the start of crystallization, is explained on the basis of the localization criterion. The calculations of the ratio T s/T m coincided well with the experimental estimates. It is indicated that the greatest value of T s/T m is likely to be characteristic of crystals with a bcc structure and a small value of the Gruneisen parameter. The ratio T s/T m has been studied at some specific points of PTs where no changes in the specific volume occurs but a finite entropy jump is observed.
Published Version
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