INFLUENCE OF COMPOSITION AND CRYSTALLITE SIZE ON THERMOELECTRIC PROPERTIES OF LAYERED TUNGSTEN DICHALCOGENIDES

A series of substitutional solid solutions W 0.98 Nb 0.02 Se 2– y Te y ( y = 0.2, 0.3, 0.4, 0.5) is synthesized and characterized, crystal lattice parameters are refined for phases of different composition. It is shown that the thermoelectric power of substitutional solid solutions based on modified tungsten diselenide W 0.98 Nb 0.02 Se 2– y Q y ( y = 0.2, 0.3, 0.4, 0.5; Q = Te, S) depends on the substitutions in the anionic sublattice. The substitution of selenium by tellurium or sulfur in tungsten diselenide leads to an increase in the crystallite sizes. The more substituted atoms in number, the larger the crystallites, both for sulfur and tellurium cases. As the concentration of sulfur or tellurium increases, electrical conductivity and the Seebeck coefficient increase non-monotonically so that the power factor PF increases in substitutional solid solutions. Among the samples of the studied series, compound W 0.98 Nb 0.02 Se 1.5 Te 0.5 has the highest PF value of 444.4 µW/m·K 2 .