Structure and stability of 2H(a)-MoS2 at high pressure and low temperatures

X-ray synchrotron diffraction (XRD) measurements of single-crystal and powder molybdenum disulfide MoS2 are performed at pressures (P) up to 78 GPa and temperatures (T) of 20 to 298 K in diamond-anvil cells. The results on single crystals demonstrate a sharp pressure induced isosymmetric phase transition of 2H(c) to 2H(a) modification at 23 GPa at 40 and 300 K. The structure of the high-pressure 2H(a) phase previously inferred theoretically and from powder XRD data is confirmed by our single-crystal XRD data solution, which also definitively determines the atomic potions as a function of pressure. No additional periodicity (commensurate or incommensurate) or distortion is found in the whole P-T range of this study. These results suggest that a previously proposed hypothetic charge-density-wave phase does not host pressure induced superconductivity experimentally found above 90 GPa.