Optical phonons in metallic high-pressure phases of Si and Ge were studied up to 50 GPa by Raman scattering. Two Raman bands (LO, TO) were observed in the β-tin phase, one of which (LO) becomes soft on approaching the transition to primitive hexagonal. For hcp-Si there is one Raman-active mode (TO), and an additional mode is observed in the stability field of Si-VI. The available theoretical results agree within (10–20)% with the experimental results.

• Received 11 December 1991

DOI:https://doi.org/10.1103/PhysRevLett.68.2232