VIBRATIONAL PROPERTIES OF THE LAYERED SEMICONDUCTOR GERMANIUM SULFIDEUNDER 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. Rama n scattering, and ab initio simulation. The theoretically and experime ntally determined pressure response of the static and dynamical proper ties are in good agreement with each other. No structural phase transf ormation is found up to 94 kbar. Inspection of the calculated eigenvec tors of zone center phonons at several pressures indicates that the va lidity of the rigid-layer mode approximation is appropriate only at ne ar-ambient pressure conditions and breaks down under compression.