Vibrational study of the superionic–protonic phase transition of (Cs) 0.26 (Rb) 0.74 H(SO 4 ) 0.89 (SeO 4 ) 0.11

Raman spectra (10–1300 cm −1 ) of polycrystalline samples of (Cs) 0.26 (Rb) 0.74 H(SO 4 ) 0.89 (SeO 4 ) 0.11 were studied from 300 to 413 K. The ν A–OH and ν A–O (A = Se, S) bands were fitted by a Lorentzian function. The simulation of the ν A–OH band allowed us to follow its evolution as a function of temperature. Above 383 K, the mixed compound exhibits a superionic phase transition. The activation energy which was determined from the plot of Δν 1/2 versus temperature for the ν A–OH band has the same order of magnitude as that determined from conductivity. Copyright © 2003 John Wiley & Sons, Ltd.