Transport and optical properties ofTi1+xS2

We report measurements of the electrical resistivity, Hall coefficient, magnetoresistance, thermoelectric power, infrared reflectivity, and $c$-axis lattice parameter of single crystals of titanium disulfide ${\mathrm{Ti}}_{1+x}{\mathrm{S}}_2$ with varying degrees of nonstoichiometry. The strong correlations we find between different measurements made on the same sample allow us to conclude that titanium disulfide is a semiconductor rather than a semimetal. Even though this fact is established, our most stoichiometric samples continue to exhibit metallic behavior, and the source of these conduction electrons is unknown. In addition, none of the scattering mechanisms examined here is capable of explaining the unusual temperature dependence of the electrical resistivity which varies as $T^3$ at low $T$ and as $T^y$ above 100 K where $y$ ranges from 1.85 for the least stoichiometric samples to 2.2 for the most stoichiometric.