Observation of low energy optical phonon in far-infrared spectra of β-phase in CuI

Abstract

Far-infrared reflectivity spectra of a sintered CuI have been measured as a function of temperature through the γ-, β- and α-phase. Three bands were observed near 120, 70 and 30 cm −1 in the β(wurtzite-type)-phase. A reststrahlen band shows a rapid broadening with increasing temperature. For the latter two bands, the possibility for the LA-mode at the A-point and the E 2-mode at the zone center is discussed, and the relationship between the frequency of low energy optical phonon mode and the ionic activation energy of the α-phase is established.