Behaviour of surface phonons in LiCsSO₄ crystal at phase transition

Abstract

The paper reports results of Brillouin spectroscopy study performed on surface phonons in different crystallographic surfaces of crystals, in a wide temperature range but with particular emphasis on the temperatures covering the phase transition. The main aim of the study is to establish in which way the ferroelastic phase transition related to a strong soft bulk mode is reflected in the near-surface region of the ferroelastic crystals. Results of the Brillouin scattering of the surface phonons propagating in the ferroelastic crystal LiCsSO 4 in the temperature range covering its phase transition are presented. Surface acoustic phonons in different planes and at various depths from the surface have been studied.

Theoretical Study of the Phonon Energy and Specific Heat of Ion-Doped LiCsSO4—Bulk and Nanoparticles

“…At the ferroelastic phase transition temperature = 202 K, both curves show a kink in agreement with Refs. [ 17 , 18 , 19 ], which is due to the spin–phonon interaction. Above , the phonon energy slightly decreases, in agreement with Refs.…”

“…The highest frequency range includes bands identified as modes derived from the stretching vibrations, specifically at = 1016 cm −1 , and , at frequencies between 1110 and 1200 cm −1 . The behavior of the surface phonons in the vicinity of the phase transition temperature was studied by Trzaskowska et al [ 18 , 19 ] using Brillouin spectroscopy. Recently, the size effects of the linear permittivity in ferroelastic LCS nanoparticles (NPs) were investigated by Milinskiy et al [ 20 ].…”