Two-Dimensional Exchange NMR and Relaxation Study of the Takagi Group Dynamics in Deuteron Glasses

Abstract

The dynamics of the deuteron glass Rb_1-x(ND₄)xD₂PO₄ has been studied with various one dimensional and two dimensional NMR techniques. Each of these techniques provides a low dimensional homomorphous mapping of the true situation, corresponding to a small piece in a huge puzzle. To create a model which is as close as possible to the true situation it is therefore necessary to combine all available macroscopic and microscopic information on the system. In this combination the NMR-techniques play a dominant role because of the broad spectral window extending from the mHz (2D NMR) to the GHz (1D NMR) region. In this contribution we show how the combination of various NMR techniques, together with symmetry relations, geometrical constraints and model calculations is leading to a consistent model of the deuteron glass dynamics. This model is based on a random Slater lattice with a certain amount of defects i.e., Takagi pairs and unpaired Takagi groups that can propagate through the lattice analogous to OH^- and OH⁺ ₃ ions in hexagonal ice.