Temperature dependence of dielectric and phonon properties in superionic conductor CuI

Roles of interionic (I) forces on the mobile defects are investigated by measuring far-infrared reflectivity (FIR) spectra of sintered CuI as a function of temperature (T) below 300 K. Anomalous increase was observed for the phonon damping constant γph and long-range Coulomb force fL. From this T-dependence and small increase of effective charge with T, we point out the effective role of the ionic character of the I force on ionic conduction.