Features of the energy spectrum and hole-scattering mechanisms in PbSb$_2$Te$_4$

The kinetic Hall $R_{ikl}$, electrical-conduction $\sigma_{kk}$, thermopower $\alpha_{kk}$ coefficients, and their anisotropy are investigated in the temperature range of 77–450 K for a series of copper-doped PbSb$_2$Te$_4$ crystals with various hole concentrations of (1.6 – 3.2) $\times$ 10$^{20}$ cm$^{-3}$. The thermopower anisotropy observed in all investigated crystals is indicative of a mixed hole-scattering mechanism. The main scattering mechanisms are scattering at acoustic phonons and at the Coulomb potential of impurities and defects. The experimental effective scattering parameters and partial mobilities are determined in the cleavage plane and along the trigonal axis. The theoretical estimates of mobility are in satisfactory agreement with the experiment. It is established that the character of the temperature dependence for the ratio $\alpha_{kk}/T=f(T)$ depends on the hole concentration. It is shown that the physical properties can be described within the framework of the one-band model for a crystal with $p_{min}$ = 1.6 $\times$ 10$^{20}$ cm$^{-3}$; the value of the effective mass density of the hole state in the main-valence band extremum is estimated as $m_d\approx$ 0.5$m_0$. The energy gap between the valence-band extrema is estimated as $\Delta E_v\approx$ 0.23 eV.