Influence of uniaxial stress on ultrasonic wave propagation near thephase transition in a TGSe crystal

Abstract

Changes in the velocity and attenuation coefficient of quasilongitudinal wavespropagating in a TGSe crystal in the directions z' = z-4°and x, induced by uniaxial stress σx and σy, were measured in the temperature range of the ferroelectric phasetransition. The uniaxial stress applied was found to shift the phasetransition temperature by ∂TC/∂σx = -0.074 and∂TC/∂σy = -0.18 K MPa-1. Othereffects appearing under the influence of external stress, such as a change inthe jump of the wave velocity at the phase transition, increase in theattenuation coefficient and broadening of the phase transition range, arediscussed on the basis of the phenomenological theory. The relaxation time ofthe order parameter fluctuations was determined. For stress exceeding 2 MPa anadditional anomaly in the wave velocity and attenuation appeared, which wasinterpreted as a splitting of the phase transition. The nonlinear elasticeffects at the phase transition, in the para- and ferroelectric phases, arealso discussed.