Phase transitions and controlled sulfurization of molybdenum oxides in vacuum

Vacuum synthesis of molybdenum disulfide (MoS 2 ) using molybdenum trioxide (MoO 3 ) and sulfur powder is presented in this study based on the equilibrium phase diagram of MoO 3 -S and MoO 2 -S at 10 Pa. The phase transitions and controlled sulfurization during the process of MoO 3 to MoS 2 were carried out in the temperature range from 673 to 1073 K, and 2H-MoS 2 were obtained by controlling the addition of sulfur powder. It was found that MoO 2 is the only detectable intermediate phase via the reactions of sulfur with MoO 3 from 673 to 973 K. The experimental findings confirmed that the sulfurization of MoO 3 to MoS 2 was a consecutive reaction with the intermediate product MoO 2 , which could be demonstrated by the results of X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive spectrometer (EDS), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). With the increases in temperature were promoted the conversion of MoO 2 to MoS 2 , and MoS 2 was formed at 1073 K with average lateral dimensions of ~ 1.30 μm. The formation of MoS 2 in vacuum was found to obey the chemical vapor transport (CVT) mechanism under the experimental condition, as the phase transition of "MoO 3 → MoO 2 → MoS 2 " was confirmed and the morphology evolutions were given in this work.