Quasielastic light scattering in superionicβ-alumina

The spectral dependence, temperature dependence, and polarization and wave-vector dependence of the quasielastic light scattering due to diffusion of ions has been studied in superionic β-alumina containing Ag, Tl, Na, K, and Rb as conducting ions. The temperature dependence of the intensity of the scattered light at a frequency shift of 3 GHz shows a behavior very similar to the temperature dependence of 1/$T_1$ obtained from NMR measurements in Ag–β-alumina and of the dielectric loss in Tl–β-alumina. The degree of depolarization of the scattered light strongly depends on the direction of the electric vectors of the incident and scattered light relative to the crystal axis. The observed polarization character is successfully explained in terms of the rotational diffusion process accompanied with creation and/or destruction of the ion pairs in the conduction plane. It is also concluded that quasielastic light scattering will be a powerful tool for measuring the ionic diffusion coefficient in transparent superionic conductors.