Influence of CDW stacking disorder on metal–insulator transition in 1T-TaS2

We have systematically studied the metal–insulator (MI) transition in 1T-Ta1−xS2 single crystals grown by the iodine vapor transport method under various sulfur pressures. From the chemical analyses and X-ray diffraction measurements, it is concluded that the obtained crystals contain Ta vacancies up to x∼5%. The MI transition temperature TMI is found to decrease with decreasing x. However, this can hardly be interpreted by the carrier doping effect on the Mott transition, in which TMI should be very sensitive to band filling, suggesting that the formation of Ta disorders in the nearly stoichiometric compounds may play an important role. STM images of a nearly stoichiometric crystal which shows no MI transition reveal characteristic mesh-like microstructures and the MI transition induced by the electric field of the STM tip. This also indicates that CDW stacking faults along the c-axis, possibly induced by Ta disorders, is important in determining the transition temperature.