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Abstract:
The effect of pressure on the zone-center optical phonon modes of
antimony in the A7 structure has been investigated by Raman
spectroscopy. The A(g) and E-g frequencies exhibit a pronounced
softening with increasing pressure, the effect being related to a
gradual suppression of the Peierls-like distortion of the A7 phase
relative to a cubic primitive lattice. Also, both Raman modes broaden
significantly under pressure. Spectra taken at low temperature indicate
that the broadening is at least partly caused by phonon-phonon
interactions. We also report results of ab initio frozen-phonon
calculations of the A(g) and E-g mode frequencies. The presence of
strong anharmonicity is clearly apparent in calculated total energy
versus atom displacement relations. Pronounced nonlinearities in the
force versus displacement relations are observed. Structural
instabilities of the Sb A7 phase are briefly addressed in the Appendix.
