Nonconservation of Excitons and the Low-Temperature Thermodynamics

The low-temperature thermodynamical analysis of the exciton system is developed in this paper. It is shown that the nonconservation of exciton number demands more correct approach to the problem than such an approach as the "u-v" transformation. The results obtained show that anharmonic temperature corrections to the polarization of the crystal are proportional to the square of the temperature.