Influence of uniaxial stress on ultrasonic wave propagation near the phase transition in a TGSe crystal
Аннотация
Changes in the velocity and attenuation coefficient of quasilongitudinal waves propagating 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 phase transition. The uniaxial stress applied was found to shift the phase transition temperature by ∂TC/∂σx = -0.074 and ∂TC/∂σy = -0.18 K MPa-1. Other effects appearing under the influence of external stress, such as a change in the jump of the wave velocity at the phase transition, increase in the attenuation coefficient and broadening of the phase transition range, are discussed on the basis of the phenomenological theory. The relaxation time of the order parameter fluctuations was determined. For stress exceeding 2 MPa an additional anomaly in the wave velocity and attenuation appeared, which was interpreted as a splitting of the phase transition. The nonlinear elastic effects at the phase transition, in the para- and ferroelectric phases, are also discussed.