The transport and thermoelectric properties of Cd doped compounds (Cd_xTi_1-x)_1+yS₂

Cadmium doped compounds (Cd_xTi_1-x)_1+yS₂ (0 ≤ x ≤ 0.075) were prepared by solid-state reaction, and their transport and thermoelectric properties were investigated from 4 K to 310 K. The results indicated that electric resistivity ρ increased first and then decreased with increasing Cd content; at low temperatures ρ-T curves for (Cd_xTi_1-x)_1+yS₂ (x > 0) was found to obey the Mott's two-dimensional hopping law ln ρ-T^-1/3. Moreover, it was found that the absolute thermopower |S| for all the doped compounds increased significantly in the whole temperature range investigated, and lattice thermal conductivity of the doped compounds rose obviously. The increase of ρ and |S| can be ascribed to decrease in electron concentration due to Cd substitution for Ti, while the slight decrease in ρ and |S| at high doping level could be caused by simultaneous intercalation of some Cd (and Ti) atoms upon heavy doping. The larger lattice thermal conductivity of the doped compounds would imply enhancement of the acoustic velocity. Besides, experiments show that the figure of merit, ZT, of the doped compound is improved in almost the whole temperature range investigated due to great enhancement of its thermopower, and specifically it reaches 0.022 at 310 K for (Cd_0.05Ti_0.95)_1+yS₂, which is about 23% larger than that of TiS₂.