6.1. Introduction

Abstract

One of the major applications of nuclear magnetic resonance (NMR) has been the study of atomic and molecular motions in solids. Because of its nuclear specificity, sensitivity to the microscopic environment of a diffusing atom, and the ability to study a variety of atomic and molecular motions over a wide temperature range, NMR has been strikingly successful in studying atomic diffusion and molecular reorientations. The chapter discusses NMR relaxation time techniques for elucidating the dynamic properties of mobile atoms and defects. In contrast to non-NMR techniques, NMR has the important advantage that the resonance signal is characteristic of the particular nucleus being studied. For this reason, NMR can normally distinguish the diffusion of a specific nuclear species from that of other nuclei. The important feature of NMR relaxation methods is that they detect motions that give rise to fluctuating local magnetic fields and can measure both local motions, such as molecular reorientations, and nonlocal motions, like translational diffusion. NMR can study a wide variety of local and nonlocal atomic motions over a wide temperature range without changing techniques. One can then directly observe changes in activation energy arising from the onset of a second motional mechanism without having the data affected differentially by artifacts because of different techniques.