Pressure-Driven Structural and Electronic Transitions in a Two-Dimensional Janus WSSe Crystal

It is the first time that the pressure-driven phase transition and metallization on a two-dimensional Janus WSSe crystal have been systematically investigated by means of a diamond anvil cell in combination with Raman spectroscopy, alternating current impedance spectroscopy, and high-resolution transmission electron microscopy coupled with first-principles theoretical calculations upon pressurization and depressurization under different hydrostatic environments. In this work, we presented the first report on the high-pressure structural stability and electrical transport characteristics in WSSe under different hydrostatic environments through Raman spectroscopy, electrical conductivity, and high-resolution transmission electron microscopy (HRTEM) coupled with first-principles theoretical calculations. For nonhydrostatic conditions, WSSe endured a phase transition at 15.2 GPa, followed by a semiconductor-to-metal crossover at 25.3 GPa. Furthermore, the bandgap closure was accounted for the metallization of WSSe as derived from theoretical calculations. Under hydrostatic conditions, similar to 2.0 GPa pressure hysteresis was detected for the emergence of phase transition and metallization in WSSe because of the feeble deviatoric stress. Upon depressurization, the reversibility of the phase transition was substantiated by those of microscopic HRTEM observations under different hydrostatic environments. Our high-pressure investigation on WSSe advances the insightful understanding of the crystalline structure and electronic properties for the Janus transition-metal dichalcogenide (TMD) family and boosts prospective developments in functional devices.