The effect of Mg substitution for Ti on transport and thermoelectric properties of TiS2

Magnesium substituted compounds MgxTi1-xS2 (0 <= x <= 0.15) were prepared by solid-state reaction, and their transport and thermoelectric properties were investigated from 5 to 310 K. The results indicate that at low temperatures (T 0) obeyed Mott's two-dimensional (2D) variable range hopping law ln sigma proportional to T-1/3 at T 0) in the whole temperature range investigated could also be attributed to the reduction of electronic concentration after doping. The thermoelectric figure of merit ZT of heavily substituted compounds (x=0.10 and 0.15) was smaller than that of TiS2, owing to the large increase of both their electrical resistivity and (lattice) thermal conductivity presumably caused by the reduced electron concentration and increased acoustic velocity, respectively. Nevertheless, ZT of the lightly substituted compound Mg0.04Ti0.96S2 enhanced substantially due to the remarkable increase in its thermopower, and specifically it is similar to 1.6 times as great as that of TiS2 at 300 K, indicating that doping (substitution) is an effective approach to enhance thermoelectric performance of TiS2. (C) 2007 American Institute of Physics.