MELTING UNDER PRESSURE AND THERMAL DEFECTS APPLICATION TO GEOPHYSICAL MINERALS

Abstract

The method of the critical concentration of thermal defects gives a linear correlation between the logarithmic derivative with respect to the volume of enthalpy of formation of one defect on the coldcompression isotherm and the pressure derivative of Poisson's ratio. This relation is applied to three minerals (KC1, NaCl and Mg„ Si 0 J . I INTRODUCTION The Lindemann law is one of the oldest and simplest criterion to describe the melting of solids, but her application to polyatomic materials is not even appropriate. In the following, we utilize another melting criterion which gives a melting curve in the (T,V) plane : the method of the critical concentration of thermal defects ; in this, the dependence of the melting temperature, T , on the pressure P is determined assuming that melting begins when the concentration of thermal defects (Frenkel or Schottky defects) reaches a critical value which remains constant along the melting curve /I/. II METHODE OF THERMAL DEFECTS AND THE KRAUT-KENNEDY MELTING LAW The criterion of the critical concentration of thermal defects gives a melting law T (V) in the form /I/ :