X-ray crystal-structure refinement of the nearly commensurate phase of 1T-TaS2 in (3+2)-dimensional superspace

The structure of the nearly commensurate phase of 1T-TaS2 (1T(2)-TaS2) has been refined in (3 + 2)-dimensional superspace against single-crystal x-ray-diffraction data collected at 300 K. The intensities of main reflections and satellites up to sixth order were measured. The unique data set in P (3) over bar consisted of 2652 observed reflections (233 main reflections, 1625 first-and second-order satellites and 794 higher-order satellites). For the refinement of the modulation amplitudes 21 harmonics on Ta and 12 harmonics on S were used. The structure agrees well with the discommensuration model proposed by Nakanishi and Shiba [J. Phys. Sec. Jpn. 43, 1839 (1977)]. The structure determination by Yamamoto [Phys. Rev. B 27, 7823 (1983)] is-in agreement with the present one, within the limited resolution of Yamamoto's refinement. In each sandwich layer there are domains forming hexagons with a diameter of about 73 Angstrom and within the center region 13-atom clusters of Ta atoms as present in the commensurate phase. It is shown that the domain structure in physical space directly corresponds to the modulation function displayed in additional space.