Large thermoelectric power factor inTiS2crystal with nearly stoichiometric composition

Abstract

A ${\mathrm{TiS}}_{2}$ crystal with a layered structure was found to have a large thermoelectric power factor. The in-plane power factor ${S}^{2}/\ensuremath{\rho}$ at 300 K is $37.1\ensuremath{\mu}{\mathrm{W}/\mathrm{K}}^{2}\mathrm{cm}$ with resistivity (\ensuremath{\rho}) of 1.7 m\ensuremath{\Omega} cm and thermopower (S) of -251 \ensuremath{\mu}V/K, and this value is comparable to that of the best thermoelectric material, ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ alloy. The electrical resistivity shows both metallic and highly anisotropic behaviors, suggesting that the electronic structure of this ${\mathrm{TiS}}_{2}$ crystal has a quasi-two-dimensional nature. The large thermoelectric response can be ascribed to the large density of states just above the Fermi energy and inter-valley scattering. In spite of the large power factor, the figure of merit $\mathrm{ZT}$ of ${\mathrm{TiS}}_{2}$ is 0.16 at 300 K, because of relatively large thermal conductivity, 68 mW/K cm. However, most of this value comes from reducible lattice contribution. Thus, $\mathrm{ZT}$ can be improved by reducing lattice thermal conductivity, e.g., by introducing a rattling unit into the inter-layer sites.