Thermoelectric properties of solid solutions with cationic and anionic substitution on the basis of layered tetradimite-like compound GeSnSb$_{4}$Te$_{8}$

The thermoelectric characteristics of the GeSnSb$_{4}$Te$_{8}$ quaternary compound and GeSnSb$_{4-x}$Bi$_{x}$Te$_{8-y}$Se$_{y}$ solid solutions were measured in a wide temperature range (300–600 K). The replacement of Sb atoms with Bi atoms and Te atoms with Se atoms leads to an increase in the thermo-emf coefficient and a decrease in the lattice component of thermal conductivity in comparison with the corresponding values for GeSnSb$_{4}$Te$_{8}$. The lower values of the lattice thermal conductivity in the alloys with $x$ = 0.6, $y$ = 0.4 in comparison with GeSnSb$_{4}$Te$_{8}$ are associated with distortions due to the difference in the atomic masses and sizes of Sb and Bi, also Te and Se atoms. It is shown that with an increase in the number of atoms participating in substitutions in both sublattices during the formation of a solid solution, the maximum of the temperature dependence of the thermo-emf and the minimum of the temperature dependence of thermal conductivity are shifted higher temperatures, which is due to an increase in the band gap. With an increase in the content of Bi and Se in solid solutions, the lattice thermal conductivity decreases and, accordingly, the thermoelectric efficiency increases. Thermoelectric figure of merit of the GeSnSb$_{4-x}$Bi$_{x}$Te$_{8-y}$Se$_{y}$ sample ($x$ = 0.6, $y$ = 0.4) has a maximum value with $Z$ = 3.34$\times$10$^{-3}$ K$^{-1}$ at 300 K.