Sulfur-catalyzed phase transition in MoS2 under high pressure and temperature

• Phase transition of MoS2 was systematically investigated under high P–T conditions.
• Sulfur-catalyzed hexagonal–rhombohedral transition was observed in MoS2.
• Phase-transition mechanisms were proposed for phase transitions.

We report phase transition and stability of MoS2 with and without the presence of sulfur melt under high-pressure and high-temperature conditions. Rhombohedral (3R) phase is found to be a high-temperature phase of MoS2 at high pressures. Excess sulfur melt catalyzes the hexagonal (2H) to rhombohedral (3R) phase transformation and lowers the conversion temperature by more than 280 K. Boundary between 2H and 3R phases has been delineated with a negative slope. Based on experimental observations, sulfur-catalyzed 2H→3R transformation mechanisms are proposed involving atomic exchange between MoS2 and sulfur, which is different from the case of without excess sulfur that proceeds through rotation and translation of the S–Mo–S sandwich layers.