On the origin of the central peak in hydrogen-bonded ferroelectrics

A microscopic theory for the central peak in H-bonded ferroelectrics is given. We obtain three different mechanisms for the formation of the central peak: a relaxation mechanism, i.e. the transverse soft mode is coupled to the longitudinal mode; an oscillatory mechanism, i.e. the transverse soft mode is coupled to the phonon mode; the third mechanism can be treated as an effective coupling between the phonon and the longitudinal modes. Copyright (C) 1996 Elsevier Science Ltd