Anisotropic mixed hole scattering mechanism in Sb$_2$Te$_{3-x}$Se$_x$ (0 $\le x\le$ 0.1) according to the data of the Nernst–Ettingshausen and seebeck effects

The temperature dependences of three independent coefficients of the Nernst–Ettingshausen tensor $Q_{ikl}$ are investigated along with the electrical conductivity, thermal voltage, and Hall coefficients of layered $p$-Sb$_2$Te$_{3-x}$Se$_x$ single crystals (0 $\le x\le$ 0.1). It is established that all $Q_{ikl}<$ 0 for the studied alloy crystals in the temperature range 77–400 K. Data on the Nernst–Ettingshausen effect and observed anisotropy of the Seebeck coefficient are indicative of the anisotropic mixed hole scattering mechanism at acoustic phonons and impurities and defects with the dominant contribution of scattering at lattice vibrations both in the crystal cleavage plane and in the trigonal axis direction. Estimation of the scattering parameters from four kinetic coefficients showed that they decrease with an increase in temperature due to phonon-scattering enhancement. They become negative at higher temperatures ($T\gtrsim$ 200 K), which is apparently associated with bandto-band hole scattering to the additional valence-band extremum.