Study of Incommensurate Phase Transition in {N(CH3)4}2ZnCl4 Crystal by Means of Ultrasound Propagation

Ultrasonic velocity and attenuation measurements for longitudinal modes propagating along the crystallographic axes of {N(CH 3 ) 4 } 2 ZnCl 4 crystal were performed over the temperature range covering the prototype, the incommensurate and the commensurate ferroelectric phases. All of measured velocities V [100] , V [010] and V [001] show clear anomalies around the prototype-incommensurate phase transition point ( T I =20^° C ), while at the incommensurate-commensurate phase transition point ( T C =7^° C ) only slight anomalies were observed. In attenuation measurements anomalies were also observed at the prototype-incommensurate phase transition point.