Principles of NMR: Its Uses in Defect Studies

Abstract

Nuclear magnetic resonance (NMR) is a well established and powerful technique for the study of molecular motions. In crystalline solids the movement of molecules, particularly the translational motion which results in self-diffusion, frequently occurs by mechanisms involving defects that are present. As discussed elsewhere in this volume, studies of mass transport properties in crystals provide very valuable insight into their defect structure. The various techniques of line-width and relaxation time measurement in NMR can therefore give very useful information which often complements data from other techniques (1). The methods of NMR can tell us about large scale motions, related to radiotracer diffusion and electrical conductivity in ionic crystals. They are also sensitive to localized movement (2,3) such as motion of atoms bound to defects giving information related to that obtained from other techniques such as dielectric relaxation and ionic thermocurrent (ITC). The NMR techniques are also nucleus specific so that we may distinguish which atomic species is mobile and even find out about systems where more than one type of atomic motion exists among the same(chemical) atomic species due, for example, to the existence of inequivalent lattice sites (4). Obvious advantages of NMR are that it can be used to study a very wide range of motional frequencies (see figure 1), so that the one basic technique can be used to study specific elements in a specific sample non-destructively over a very wide temperature (or pressure) range.