Lattice Instability of Cs2HgCl4 Crystals

• Published in: physica status solidi (b) Vol. 211; no. 2; pp. 631 - 640
• Main Authors: Kityk, A. V., Shchur, Ya.I., Zadorozhna, A. V., Trach, I. B., Girnyk, I. S., Martynyuk-Lototska, I.Yu, Vlokh, O. G.
• Format: Journal Article
• Language: English
• Published: Berlin WILEY-VCH Verlag 01-02-1999; WILEY‐VCH Verlag
• ISSN: 0370-1972; 1521-3951
• DOI: 10.1002/(SICI)1521-3951(199902)211:2<631::AID-PSSB631>3.0.CO;2-1

The lattice dynamics of Cs2HgCl4 crystals and its relation to the pressure induced proper ferroelastic instability is analyzed using a rigid‐ion model in the quasiharmonic approximation. Such a simple model is already sufficient to reproduce the lattice instability leading to appearance of the proper ferroelastic phase transition. It has been shown that the lattice loses its stability with respect to the transverse acoustical mode TAZ(k ∥ b), whereas the soft optical mode (B3g symmetry at k = 0) remains stable. This fact is in agreement with the phenomenological theory.