Ultrasonic frequencies correlated with the volume changes of the q[110] mode for the first-order phase transition in NH4CI

Abstract

Abstract We correlate here by means of γ-Gruneisen relations the volume changes with the ultrasonic frequencies of the q[110] mode of NH4Cl for the first-order phase transition in this crystal. The ultrasonic frequencies were calculated by a method, which we have developed, using the length-change data from the literature at pressures of 0, 0.2, 0.4 and 0.6 kbar in the first-order phase region of NH4Cl. Our calculated frequencies are in very good agreement with the observed data from the literature for the q[11 0] mode at these pressures. This shows that by correlating the volume changes with the ultrasonic frequencies, the observed behaviour of NH4Cl can be explained adequately near the first-order phase transition in this crystalline system.