Soft mode from the boundary of the Brillouin zone in the Raman-scattering spectrum of the paraphase of Hg2CI2 and Hg2Br2
Barta C. , Zadokhin B.S. , Kaplyanskii A.A., Markov Yu.F.
Using the extrinsic ferroelastics Hg2Cl2 and Hg2Br2 as an example, we have observed, for the first time in phase transitions, the appearance of a soft mode from the boundary of the Brillouin zone (BZ) in the Raman scattering spectrum (RSS) of the paraphase (T> Tc). The singularities of the RSS show it to be a first-order spectrum induced by structural disturbances of the lattice.