Thermoelectric properties of Ti1+xS2 prepared by CS2 sulfurization

Titanium disulfide (TiS2) powder was prepared by sulfurizing TiO2 powder with CS2 gas at 1073 K for 4 h. Because CS2 gas is a powerful sulfurizing agent for TiO2, CS2 sulfurization can be performed at a low temperature. The TiS2 powder thus prepared was first mixed with sulfur powder in a mass ratio of 1:0.04 and pressure sintered at 973 K for 1 h under a uniaxial pressure of 50 MPa in vacuum. The addition of a small amount of sulfur powder to the TiS2 powder prevents sulfur deficiency in the sintered compact, resulting in the formation of a near-stoichiometric Ti1.008S2 composition. X-ray diffraction patterns show that the crystalline ab-axis is preferentially oriented perpendicular to the pressing direction. The Seebeck coefficient, electrical resistivity and thermal conductivity of the oriented TiS2 sintered compacts with near-stoichiometric and sulfur-poor (titanium-rich) compositions were measured in the temperature range 300-723 K. The thermoelectric figure of merit ZT was enhanced by prevention of sulfur deficiency and formation of the oriented texture. The highest ZT of 0.34 was observed at 663 K in Ti1.008S2 for the direction perpendicular to the pressing axis. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.