NIR Raman studies of molecular dynamics in superionic (NH4)(4)H-2(SeO4)(3)

Results of NIR Raman studies of (NH4)(4)H-2(SeO4)(3) Single crystals in the temperature range from 100 to 403 K are presented. The Raman spectra of th e crystal do not change on cooling from room temperature to 100 K. Changes in the spectrum observed on heating the crystal to the superionic phase (T > T-s = 403 K) point to highly isotropic structural disorder. When the crys tal is cooled from the highly disordered superprotonic phase to T much less than T-s the order characteristic of the low temperature phase (ordered tr imers) has to be recovered. The recovery process was studied at 298 and 308 K in the time scale to 2000 s. (C) 2000 Elsevier Science B.V. All rights r eserved.