Ferroelastic phase transition in K3Na(SeO4)2: Brillouin-scattering studies and theoretical modeling

Authors:

• Bogusław Mróz,
• H. Kiefte,
• M.J. Clouter,
• J.A. Tuszyński

Abstract

High-resolution Brillouin spectroscopy was used to study the elastic properties of ferroelastic K3Na(SeO4)2. The temperature dependence of nine Brillouin modes of the acoustic phonons propagating in the [100], [010], [001], and [011] directions were measured in the temperature range 290-380 K. These results indicate a 3̄m→2/m transition at Tc=334 K followed, by approximately 12 K, by a transition involving an unknown mode Q. Mode softening in the c66 and c44 elastic constants results from the main first-order transition while an additional softening in c33 and c44 is due to coupling with Q. A Landau-type free-energy expansion has been postulated and discussed in order to explain the qualitative features of the system. © 1992 The American Physical Society.