A General Theory of Heterophase Fluctuations and Pretransition Phenomena

Abstract

The present paper is a generalization of a preceding note on the statistical theory of condensation phenomena. It is based on the idea that the macroscopic transition of a substance from a phase A to a phase B is preceded by the formation of small nuclei of the B phase within A, these nuclei being treated as resulting from ``heterophase'' density fluctuations or as manifestations of a generalized statistical equilibrium in which they play the roles of dissolved particles, whereas the A phase can be considered as the solvent. The application of the general theory to premelting phenomena in crystals leads to a quantitative explanation of the abnormal increase of the specific heat of the thermal expansion coefficient (and of the electric conductivity, in the case of ionic substances) in the close neighborhood of the conventional melting point, with the result that the surface tension between a crystal and its melt must be of the order of 1 dyne/cm. This result is checked by a calculation of the temperature corresponding to the highest crystallization rate of an overcooled liquid. Transitions of higher order and Curie points are also briefly discussed from the same point of view.