Ferroelastic crystals and their nonlinear elastic properties observed in frequency range from gigahertz to milihertz

Abstract

The experiments reported in this article have been performed to unify the results of earlier and recent determinations of parameters describing the elastic properties of Rb 4 LiH 3 (SO 4 ) 4 , LiCsSO 4 (LCS) and KH 2 PO 4 crystals measured by different experimental methods. The above crystals undergo a second-order phase transition, incommensurate phase transition (PT) and a first-order but close to second-order phase transition, respectively. To investigate the elastic properties of the crystals in the frequency range from 10 À1 to 10 10 Hz, five experimental methods were applied: dynamic mechanical analysis, piezoelectric resonance, composite oscillator bar, ultrasonic wave propagation and Brillouin light scattering. The results of the experiments allowed identification of the processes contributing to the elastic response of the crystals investigated. Moreover, for the LCS crystal a model of the incommensurate PT was presented.

Piezoelectric softening in ferroelectrics: Ferroelectric versus antiferroelectricPbZr1−xTixO3

“…The smallness of the softening in the Brillouin experiments compared to those at lower frequency has been noticed also for other FE materials, and explained in terms of dynamic response of the order parameter and domain wall motion [28], but besides relaxation and adiabatic versus isothermal effects, the piezoelectric stiffening from the depolarization field should also be taken into account.…”

Depression of the ferroelastic phase transition in LiCsSO4 by uniaxial stress

“…This indication has been confirmed by Electron Paramagnetic Resonance (EPR) results [16,17]. The study of changes in the elastic properties of the crystal in the range of the phase transition by the method of Dynamic Mechanical Analysis (DMA) [18,19] has revealed an elastic anomaly in the range 190 − 195 K, i.e. at temperatures other than the classical ferroelastic phase transition point.…”

“…This phase shows an incommensurate ordering manifested in the Raman scattering spectra by changes in the low-frequency vibrations of the crystal lattice [39]. Moreover, at 196 K a reorganisation of the ferroelastic domain structure was observed [1,16,18], and an additional anomaly in the elastic properties of the crystal was detected by the method of dynamic mechanical analysis [18]. Kurzyński et al, who studied the Ising model in which pseudo-spins corresponded to the rotations of SO 4 tetrahedra, concluded that in the phase below T C the ferroelastic and incommensurate types of ordering co-existed.…”

Temperature‐dependent low wavenumber Raman scattering studies in LiCsSO4 crystal

“…The ferroelastic domain structure change was observed in the temperature range 201 K < T < 189 K 19. Below 189 K down to 140 K, the structure remained unchanged.…”