Vibrational properties of the layered semiconductor germanium sulfide under hydrostatic pressure: Theory and experiment

The structural and vibrational properties of the prototypical layered semiconductor germanium sulfide (GeS) have been studied under pressure using a combination of high-resolution x-ray powder diffraction, Raman scattering, and ab initio simulation. The theoretically and experimentally determined pressure response of the static and dynamical properties are in good agreement with each other. No structural phase transformation is found up to 94 kbar. Inspection of the calculated eigenvectors of zone center phonons at several pressures indicates that the validity of the rigid-layer mode approximation is appropriate only at near-ambient pressure conditions and breaks down under compression.