Thermoelectric properties of W _1−x Nb _x Se _2−y S _y polycrystalline compounds

We investigate the thermoelectric properties of bulk polycrystalline samples of WSe ₂ -based compounds with partial substitutions in the cationic (W) and the anionic (Se) sublattices in the temperature range from 4.2 to 650 K. The substitution of W for Nb leads to a significant increase in the charge carrier concentration, however, deteriorates the charge carrier mobility. In contrast, the substitution of selenium for sulfur increases the charge carrier mobility, the thermal conductivity, and the Seebeck coefficient but conductivity changes non-monotonical. We show that the addition of sulfur in anionic sublattice affects the grain sizes in the polycrystalline material. Using substitutions in the anionic and cationic sublattices, we find the optimal ratio of the elements for better thermoelectric efficiency. The W _0.98 Nb _0.02 Se _1.7 S _0.3 sample showed the best value of the figure of merit ZT = 0.26 (T = 650 K).