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

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.