Large Thermoelectric Power Factor in TiS2 Crystal with Nearly Stoichiometric Composition

Abstract

A TiS${}_2$ crystal with a layered structure was found to have a large thermoelectric power factor.The in-plane power factor $S^2/\rho$ at 300 K is 37.1~$\mu$W/K${}^2$cm with resistivity ($\rho$) of 1.7 m$\Omega$cm and thermopower ($S$) of -251~$\mu$V/K, and this value is comparable to that of the best thermoelectric material, Bi${}_2$Te${}_3$ alloy. The electrical resistivity shows both metallic and highly anisotropic behaviors, suggesting that the electronic structure of this TiS${}_2$ crystal has a quasi-two-dimensional nature. The large thermoelectric response can be ascribed to the large density of state just above the Fermi energy and inter-valley scattering. In spite of the large power factor, the figure of merit, $ZT$ of TiS${}_2$ is 0.16 at 300 K, because of relatively large thermal conductivity, 68~mW/Kcm. However, most of this value comes from reducible lattice contribution. Thus, $ZT$ can be improved by reducing lattice thermal conductivity, e.g., by introducing a rattling unit into the inter-layer sites.

11 pages, 4 figures, to be published in Physical Review B