Raman measurements of the superionic conductor AgI

Using the Raman technique, we have observed large abrupt reversible changes in the phonon spectrum at the transition temperature, T_c = 147°C, of the superionic conductor AgI. The defect nature of the high temperature phase completely breaks down the selection rules and allows the Raman measurements to give a measure of the frequency dependent conductivity, σ(ω), assuming a frequency independent matrix element. Similarities as well as differences in σ(ω) above and below T_c are shown.