Large Thermoelectric Power Factor in TiS2 Crystal with Nearly Stoichiometric Composition

A TiS2 crystal with a layered structure was found to have a large thermoelectric power factor. The in-plane power factor S/ρ at 300 K is 37.1 μW/Kcm with resistivity (ρ) of 1.7 mΩcm and thermopower (S) of -251 μV/K, and this value is comparable to that of the best thermoelectric material, Bi2Te3 alloy. The electrical resistivity shows both metallic and highly anisotropic behaviors, suggesting that the electronic structure of this TiS2 crystal has a quasi-twodimensional 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 TiS2 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. PACS numbers: 72.15.Eb, 72.15.Jf, 81.05.Bx Typeset using REVTEX