Mechanism of proton conductivity in quasi-one-dimensional hydrogen-bonded crystals

The microscopic mechanisms of proton transport in partially deuterated ammo nium hydrogen selenate [NH4HSeO4 (AHSe)] and partially deuterated mixed cry stals of betaine phosphate (DBP) and betaine phosphite (DBPI) (DBP1-xDBPIx) were studied by means of one-dimensional Fourier transform H-2 NMR, two-di mensional (2D) H-2 NMR and dielectric measurements. Slow chemical exchange processes of deuterons between different hydrogen bridges occur which can b e studied by means of the 2D H-2 NMR technique over a wide temperature rang e. In both systems, AHSe and DBP1-xDBPIx, the ionic conductivity is probabl y realized via jumps of the protons or deuterons between different hydrogen bonds (inter-bond jumps). The importance of certain defects for the conduc tivity process is clearly revealed. In AHSe, jumps occur through non-occupi ed hydrogen positions. In the mixed crystals DBP1-xDBPIx, the creation of d efects is in fact favoured by the substitution of DBP for DBPI molecules or vice versa. The creation of vacancies may be explained by the occurrence o f defects in the lattice structure, e.g. on the basis of the known Grotthui s mechanism and a multi-dimensional conductivity model as suggested for KDP . Copyright (C) 2001 John Wiley & Sons, Ltd.