Raman spectroscopic investigations on transition-metal dichalcogenides MX2 (M = Mo, W; X = S, Se) at high pressures and low temperature

Transition‐metal dichalcogenides have been investigated using Raman spectroscopy both being off‐resonance and in resonance. The first‐order Raman spectra of MoS2, MoSe2, WS2 and WSe2 single crystal synthesized by vapor transport technique have been studied as a function of hydrostatic pressure (0–20 GPa) and temperature (80–300 K). Isobaric and isothermal mode‐Grüneisen parameters have been determined from the temperature and pressure‐dependent Raman spectra. The pressure dependence of the chalcogen–chalcogen and metal–chalcogen force constant has been obtained using a central force model. Separation of the temperature dependence of Raman mode wavenumbers into quasi‐harmonic and purely anharmonic contributions using measured high‐pressure Raman data allows us to extract the changes in the phonon wavenumbers arising exclusively due to anharmonic interactions. Copyright © 2014 John Wiley & Sons, Ltd. The Raman spectrum study on transition‐metal dichalcogenides crystals indicates good structural stability at high pressure up to 20 GPa and low temperature up to 80 K. The pressure dependence of the force constants has been calculated using a central force model. The mode‐Grüneisen parameters have been determined from the temperature and pressure‐dependent Raman spectra. The analysis presented here is important for understanding the anharmonic nature of phonons in these compounds.