Abstract
Temperature dependences of diagonal elements of the elastic stiffness constant in [N(CH3)4]2ZnI4 single crystal have been measured between room temperature and about 200K by means of the ultrasonic pulse echo overlap method. In the room temperature phase (phase I), softening of the elastic constant c55 has been observed. The transition temperature has been determined to be TC1=256K. The second elastic anomaly of phase transition has been observed at TC2=213K.