Stoichiometry dependence of the transport properties of TiS2

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Abstract
Transport and Raman data are presented for samples of Ti1+xS2 with carrier densities, determined from the Hall coefficient, ranging from approximately 1020 cm-3 to approximately 3*1021 cm-3. No dependence on carrier concentration, n, is observed for the frequency of the A1g Raman-active phonon, whereas a strong variation is seen in the non-linear temperature dependence of resistivity, rho (T), between 4.2K and 290K. Fitting the resistivity to a power law, rho (T)- rho (o) varies as Tp, in the range 110K to 290K, the authors find p=2.3 for n approximately 1020 cm-3 and p=1.6 for n approximately *1021 cm-3. For samples with carrier concentrations above approximately 7*1020 cm-3 a stronger temperature dependence is observed below 100K. The temperature-dependent part of the resistivity is proportional to n-0.74 at room temperature and n-0.60 at 150K. It is argued that the scattering mechanism in TiS2 is with both optical and acoustic phonons. Below the Debye temperature the form and variation with carrier concentration of the temperature dependence may be described by a model involving both intra- and inter-valley scattering by acoustic phonons.