Enhanced thermoelectric performance of TiS2 via large thermal conductivity reduction by solid solution alloying with TiSe2

TiS 2 is a transition metal dichalcogenide with semiconducting transport properties, and is considered a potential thermoelectric material owing to its relatively low lattice thermal conductivity originated from van der Waals stacking. In this study, the evolution of electrical and thermal transport properties of TiS 2 by solid solution alloying with TiSe 2 are investigated systematically regarding thermoelectric properties. A series of solid solution compositions of Ti(S 1 − x Se x ) 2 ( x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5) polycrystalline samples was synthesized by a conventional solid-state reaction, wherein no secondary phase was formed. As x increased, the electrical conductivity and carrier concentration gradually increased, while the Seebeck coefficient decreased. Consequently, the power factor decreased. On the other hand, the lattice thermal conductivity is reduced largely to 0.96 W/mK for x = 0.5 at 300 K, compared to 2.3 W/mK for the pristine TiS 2 sample. Consequently, the thermoelectric figure of merit zT of TiS 2 was enhanced by solid solution allying with TiSe 2 , despite deterioration of the electrical transport properties. The maximum zT of 0.41 was observed for x = 0.4 (Ti(S 0.6 Se 0.4 ) 2 ) at 500 K.