Improved thermoelectric properties of layered Ti 1− x Nb x S 2− y Se y 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 Ti 1− x Nb x S 2− y Se y solid solutions was found. The Fermi energy E F2D was estimated using the temperature dependences of Seebeck coefficient. The relationship between the Fermi energy E F 2 D and figure of merit ZT was established. The effect of sintering on parameters σ ( T ), S ( T ), charge carrier concentration ( n 2D ), mobility ( µ ), and thermal conductivity ( k ) was found. The optimal value of Fermi energy E F2D in terms of figure of merit ZT = 0.31 at room temperature ( T = 300 K) was found for Ti 0.98 Nb 0.02 S 1.3 Se 0.7 sample sintered at 600°C.