Infrared Study of the Pressure-Induced Isostructural Metallic Transition in Mo0.5W0.5S2

Ternary compounds of transition metal dichalcogenides are emerging as an interesting class of crystals with tunable electronic properties, which make them attractive for nanoelectronic and optoelectronic applications. Among them, MoxW1-xS2 is one of the most studied alloys due to the well-known and remarkable features of its binary constituents, MoS2 and WS2. The band gap of this compound can be modeled varying Mo and W percentages in the sample, and its vibrational modes result from a combination of MoS2 and WS2 phonons. In this work, we report transmission measurements on a Mo0.5W0.5S2 single crystal in the far-infrared range. Absorbance spectra collected at ambient conditions enabled for the first time a classification of the infrared-active phonons, complementary to Raman studies. High-pressure measurements allowed the study of the evolution of both the lattice dynamics and the free carrier density up to 31 GPa, suggesting the occurrence of an isostructural semiconductor-to-metal transition above 18 GPa, in very good agreement with the theoretical calculation reported in the literature.