Band structure and processes in the electronic system of crystals (Bi$_{2-x}$Sb$_{x}$)Te$_{3}$ (0 $<x<$ 2) according to optical studies in the infrared range

The decrease in the resonance frequency of plasma oscillations of free charge carriers omegap with increasing temperature observed in Bi$_{2-x}$Sb$_{x}$ (0 $<x<$ 2) $p$-type crystals can only be partially explained by an increase in the polarization background of the crystal $\varepsilon_\infty$. Analysis of the experimental data suggests that the temperature change in omegap observed in the range from 80 to 300 K is also due to a decrease in the ratio of the concentration of free charge carriers to their effective mass $p/m^*$. This can be explained by an increase in the effective mass of carriers with increasing temperature, as well as by the process of hole redistribution between nonequivalent extrema of the valence band, the existence of which is confirmed by the regularities of the temperature change in the optical band gap observed in the reflection spectra of infrared radiation.