Lattice vibrations were investigated by Raman spectroscopy in the layered materials $2H$-Mo${\mathrm{S}}_2$ up to 180 kbar, $2H$-Mo${\mathrm{Se}}_2$ up to 180 kbar, and $2H$-Mo${\mathrm{Te}}_2$ up to 80 kbar. One $A_{1g}$ and two $E_{2g}$ modes were observed. The energies of the rigid-layer modes rapidly increase with pressure, but the increase becomes slow above 50 kbar. The interlayer and intralayer shear force constants are obtained as a function of pressure with the use of the linear-chain model.

• Received 8 January 1982

DOI:https://doi.org/10.1103/PhysRevB.26.6554