Improved thermoelectric properties of layered Ti1−xNbxS2−ySey solid solutions.

The thermoelectric properties of a series of the polycrystalline samples of titanium dichalcogenides with partial substitution of Ti for Nb and S for Se were investigated. It was found that sintering of the samples improved the thermoelectric efficiency (ZT), and the maximum ZT was achieved at sintering temperature of 600°C. A further increase in the sintering temperature (850°C and 950°C) led to the recrystallization of the samples, as a result, the Seebeck coefficient sharply decreased and electrical conductivity dramatically increased. The temperature dependences of electrical conductivity σ(T) in the temperature range from 4.2 to 300 K and Seebeck coefficient S(T) in the temperature range from 77 to 300 K were investigated in order to determine the nature of the observed improvements in thermoelectric properties due to double substitutions and sintering. Two‐dimensionalization of electron transport properties of Ti1−xNbxS2−ySey solid solutions was found. The Fermi energy EF2D was estimated using the temperature dependences of Seebeck coefficient. The relationship between the Fermi energy EF2D and figure of merit ZT was established. The effect of sintering on parameters σ(T), S(T), charge carrier concentration (n2D), mobility (µ), and thermal conductivity (k) was found. The optimal value of Fermi energy EF2D in terms of figure of merit ZT = 0.31 at room temperature (T = 300 K) was found for Ti0.98Nb0.02S1.3Se0.7 sample sintered at 600°C. [ABSTRACT FROM AUTHOR]