A role of non-hydrogen framework vibrational modes in formation of ferroelectric properties of H-bonded K3H(SO4)2-like materials

An effect of molecular vibrational modes within the dimers [O3AO–(H/D)· · ·OAO3]32 on behavior of H-bond protons or deuterons is studied theoretically for H-bonded antiferroelectrics and quantum paraelectrics of theM3(H/D)(AO4)2 family (M ¼ alkali metal, A ¼ S, Se). The ‘heavy’ reorganization modes in D-species of this family and both reorganization and promoting modes in corresponding H-analogues are examined. It is shown that the analysis with due regard for the reorganization modes results in insignificant decreasing of the effective tunneling frequency of light nuclei. Hence the reasonable estimations of the critical temperature of the low-temperature phase transition in M3D(AO4)2 materials are available only with additional corrections related to potential profiles of a deuteron. It is noted that in the limits of the proposed model the promoting mode in the case of H-species can favor, in principle, the increasing as well as the decreasing of effective proton level splitting. q 2004 Elsevier B.V. All rights reserved.