Uniaxial stress dependence of the elastic wave propagation near normal—incommensurate phase transition in (NH4)2ZnCl4

Abstract

The effect of uniaxial σ2 stress on the velocity and attenuation of longitudinal ultrasonic wave propagating along the [001] direction in an NH4)2ZnCl4 crystal was studied in the vicinity of the orthorhombic — incommensurate phase transition. A stress induced shift of the transition temperature is dT1/dσ2= 0.2 K/MPa. Application of stress greater that 5 MPa results in the appearance of additional anomalies of velocity and attenuation, which are interpreted as manifestations of a new phase induced by uniaxial Stress.