Chemical ordering and pressure-induced isostructural and electronic transitions in MoSSe crystal

Isostructural transitions in layered MX2 compounds are governed by competing van der Waals (vdW) and Coulomb interactions. While an isostructural transition (at P∼ 20 GPa) has been observed before metallization in MoS2 when subjected to pressure, it is surprisingly missing in layered MoSe2 and MoTe2. Using synchrotron x-ray diffraction and Raman spectroscopic measurements of structural and vibrational properties of layered MoSSe crystals subjected to pressures up to 30 GPa and first-principles density functional theoretical analysis, we demonstrate a layer sliding isostructural transition from its 2H′c structure (space group P63mc) to a mixed-phase of 2H′a+2H′c at P∼ 10.8 GPa, marked by discontinuity in lattice parameters, pressure coefficients of Raman modes, and accompanying changes in electronic structure.