Ultrasonic attenuation and phase velocity measurements as a function of temperature and frequency are reported in the $\beta$ phase of AgI. Below about 50 MHz the dominant effect is the piezoelectric coupling between the mobile ions and the ultrasonic waves; an analysis similar to that of Hutson and White for piezoelectric semiconductors gives good agreement. Above 50 MHz this interaction becomes screened. An additional attenuation mechanism is observed at 540 MHz.

• Received 15 February 1979

DOI:https://doi.org/10.1103/PhysRevLett.42.1684