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

TiS₂ 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 TiS₂ by solid solution alloying with TiSe₂ 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 TiS₂ sample. Consequently, the thermoelectric figure of merit zT of TiS₂ was enhanced by solid solution allying with TiSe₂, despite deterioration of the electrical transport properties. The maximum zT of 0.41 was observed for x = 0.4 (Ti(S_0.6Se_0.4)₂) at 500 K.