Ultrasonic attenuation in a LiIO3 crystal

The temperature dependences of the attenuation of longitudinal acoustic waves along the x axis of a LiIO₃ crystal are studied experimentally by the method of Bragg diffraction of light by ultrasound. The measurements are performed in the temperature range from 215 to 335 K at frequencies of 400–690 MHz. Above 260 K, the attenuation is found to exhibit a frequency-independent growth of a relaxational character, which is used to calculate the enthalpy of the activation of ionic motion in the direction normal to the hexagonal axis. In addition, resonance attenuation peaks are observed; as the frequency increases, the peaks are shifted toward lower temperatures. A phenomenological model is proposed to explain the origin of the resonance absorption.