Phonon Dispersion and Pressure Behavior of Hg₂Cl₂ Crystals

Abstract

The dispersion dependences of frequencies of acoustic and optical phonons are calculated and constructed, and the density of states of the phonon spectrum is obtained for Hg₂Cl₂ crystals. The influence of the hydrostatic pressure on frequencies of acoustic and optical phonons and their dispersion is analyzed theoretically. It is revealed that an increase in the pressure leads to a considerable softening of the slowest acoustic TA branch (soft mode) at the X-point of the Brillouin zone boundary. This behavior is consistent with the phenomenological Landau theory and correlate with experiments.

Keywords:

• Ferroelastic
• phase transition
• dispersion branch

Acknowledgments

This study was supported by the Russian Foundation for Basic Research (project no. 09-08-00739), the Presidium of the Russian Academy of Sciences (Program P-03), the grant for young scientists, young PhD of universities and academic institutes of Saint-Petersburg.