H-2 nuclear magnetic resonance studies on the deuteron dynamics in betainephosphate/phosphite mixed crystals

One- and two-dimensional H-2 NMR measurements on selected single crystals o f deuterated betaine phosphate/phosphite mixed crystals (DBP1-xDBPIx) in th e antiferrodistortive and paraelectric phases were performed in order to st udy the static and dynamic behaviour of the deuterium atoms in the hydrogen bridges and in the methylene groups. In the H-2 nuclear magnetic resonance (NMR) spectra of the mixed crystals, it is possible to distinguish between DBP and DBPI molecules. Furthermore, for all deuterons the electric field gradient (EFG) tensors could be determ ined. A characteristic dependency of the high-temperature phase transition on the phosphite concentration x was derived from the changes of the one-di mensional H-2 NMR spectra. Our suggested model, which describes this depend ency qualitatively, underlines the antiferrodistortive character of this tr ansition. Furthermore, from the line-shape variations, the occurrence of pr ocesses of exchange between several deuterons, including DBP and DBPI molec ules, was concluded. The presence of exchange between different molecules i n the chains was confirmed by means of analysing the cross-peaks of two-dim ensional H-2 NMR exchange experiments. The observation of this charge-trans port process along the chains from the microscopic point of view is very im portant for the understanding of electrical conductivity processes in these crystals.