Synthesis and thermoelectric properties of solid solution Sn$_{1-x}$Pb$_x$Sb$_4$Te$_8$ doped with bismuth

The thermoelectric properties of the solid solution Sn$_{1-x}$Pb$_x$Sb$_4$Te$_8$ and Sn$_{1-x}$Pb$_x$Sb$_{4-y}$Bi$_y$Te$_8$ ($y$ = 0.4, 0.8, 1.2) were measured in a wide temperature range (100–800 K). The substitution of Bi atoms for Sb 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 properties of the solid solution Sn$_{1-x}$Pb$_x$Sb$_4$Te$_8$. The lower values of the lattice thermal conductivity in alloys $y$ = 1.2 in comparison with the solid solution Sn$_{1-x}$Pb$_x$Sb$_4$Te$_8$ are associated with distortions due to the difference in the atomic masses and sizes of Sb and Bi atoms. With an increase in the Bi content in solid solutions, the lattice thermal conductivity decreases and, accordingly, the thermoelectric efficiency increases. Thermoelectric figure of merit Sn$_{1-x}$Pb$_x$Sb$_{4-y}$Bi$_y$Te$_8$ ($y$ = 1.2) has a maximum value of $Z$ = 3.2$\cdot$10$^{-3}$ at 300 K.