Soft mode at the boundary of the Brillouin zone and nature of the phase transition in monovalent mercury-halide crystals
Barta I.I., Kaplyanskii A.A., Kulakov V.V., Markov Yu.F.
With Hg2Cl2 and Hg2Br2 as examples, we observed for the first time a soft mode in pure ferroelastics. The soft mode was observed in the Raman scattering spectra (RSS) at temperatures below the point of the D 4h-D 2h structure phase transition. A model of the phase transition is proposed on the basis of an investigation of the singularities of the RSS.