Effective mass, mobility of charge carriers, and lattice thermal conductivity in nanocomposite thermoelectrics based on bismuth and antimony chalcogenides

In $p$-type thermoelectrics based on bismuth and antimony chalcogenides with a bismuth excess, the effective mass of the density of states $m/m_0$ increases in nanocomposite and nanostructured solid solutions compared with the base material obtained by the direct crystallization method. It is shown that an increase in $m/m_0$ is associated with an increase in the effective scattering parameter $r_{\operatorname{reff}}$ and strengthening of the dependence of the relaxation time on energy, which is typical for topological insulators. The material parameter $\beta$, proportional to the thermoelectric efficiency of ZT, at temperatures below room temperature increases greater in the nanostructured composition than in the nanocomposite with the inclusions of SiO$_2$ due to the growth of $m/m_0$ and a decrease in the lattice thermal conductivity $\kappa_{\mathrm{L}}$. At high temperatures in the range of 300–500 K, the greatest growth in parameter $\beta$ in the base material is associated with higher mobility.