Ultrasonic attenuation of silver ions in RbAg4I5single crystals

The attenuation of longitudinal waves propagating in the [100] direction in high-ionic-conductivity Rb${\mathrm{Ag}}_4$ ${\mathrm{I}}_5$ is studied as a function of frequency from 15 to 45 MHz and temperature from 170 to 370 K. By virtue of the temperature dependence, it is concluded that the origin of an appreciable fraction of the attenuation in Rb${\mathrm{Ag}}_4$ ${\mathrm{I}}_5$ at high temperatures are silver ions contributing to the electric conductivity. The activation energies obtained from the temperature dependence of the attenuation due to mobile ions lie between 0.06 and 0.12 eV, which values are very close to that observed for conduction processes. On the basis of proximity in activation energy, the attenuation caused by mobile silver ions is determined as being proportional to the electric conductivity. On the other hand, by virtue of the frequency dependence, it is determined that the absorption due to silver ions is roughly proportional to the square of the frequency. The motions of silver ions in Rb${\mathrm{Ag}}_4$ ${\mathrm{I}}_5$ may be explained in terms of a hopping transport model.