Character of interaction in the SnSb$_{2}$Te$_{4}$–SnBi$_{2}$Te$_{4}$ system and the thermoelectric properties of (SnSb$_{2}$Te$_{4}$)$_{1-x}$(SnBi$_{2}$Te$_{4}$)$_{x}$ solid solutions

For the first time, the character of the interaction of components along the cut of SnSb$_{2}$Te$_{4}$–SnBi$_{2}$Te$_{4}$ is studied by various physicochemical methods in a wide temperature range, and the phase diagrams are plotted. The cut is found to be a quasi-binary cross section of the SnTe–Sb$_{2}$Te$_{3}$–Bi$_{2}$Te$_{3}$ quasi-ternary system. The cut contains the quaternary compound SnSbBiTe$_4$, which melts congruently at 900 K. Single crystals of the quaternary compound SnSbBiTe$_4$ are obtained by the method of chemical transport reactions. X-ray analysis is used to determine the unit-cell parameters $a$ = 4.356 $\mathring{\mathrm{A}}$ and $c$ = 41.531 $\mathring{\mathrm{A}}$ of single crystals of the quaternary compounds. It is found that the compound crystallizes in the tetradymite lattice of rhombohedral syngony, space group R$\bar3$m, the charge is $z$ = 3, and the unit-cell volume is $V$ = 682.43 $\mathring{\mathrm{A}}^3$. The thermoelectric parameters of (SnSb$_{2}$Te$_{4}$)$_{1-x}$(SnBi$_{2}$Te$_{4}$)$_{x}$ are measured in the temperature range of 300–600 K. It is found that the thermoelectric figure of merit increased with the SnBi$_{2}$Te$_{4}$ content in the solid solutions. The thermoelectric efficiency of (SnSb$_{2}$Te$_{4}$)$_{1-x}$(SnBi$_{2}$Te$_{4}$)$_{x}$ with $x$ = 1.0 has a peak value of $Z$ = 3.1 $\times$ 10$^{-3}$ K$^{-1}$ at 300 K.