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Abstract
This work is devoted to the study of structural relaxation in superionic crystals with hydrogen bonds at the recovery of the low temperature phase structure after fast cooling from the superionic phase. The results of experimental investigations of this phenomenon in (NH4)4H2(SeO4)3 crystal by means of Raman spectroscopy are given. It follows that superitonc-ferroelastic transition is connected with the transformation from delocalization of protons to their localization and that the creation of the ordered state of protons with definite space symmetry takes place after their localization. To explain this effect the microscopic approach, based on the proton ordering model and taking into account thermally activated proton hopping and quasi-polaron effect resulting from the interaction of protons with the optical phonons, is proposed.