INVERSION OF ATOM POPULATIONS OF CRYSTAL SITES AT PHASE-TRANSITIONS

It is shown that at structural phase transitions of first order in the case of the existence of two energy minima per atom in the unit cell and in the vicinity of the phase interface an inversion of the atom populations of crystal sites arises. This phenomenon is explained by the retardation in establishing the equilibrium atom population as compared with establishing the equilibrium values of energy. The system of kinetic equations for the order parameter are solved numerically. If the Landau approximation of the free energy is valid, analytic solutions for order parameter and inverse population are obtained. The peculiarities of the inversion development for different models of phase transitions are considered. The appearance of inversion can cause various coherence effects (acceleration of atoms, emission of electromagnetic waves, emission of sound, etc.).