NMR Relaxation Measurements and Defect Mobility Studies in Ionic Materials

The measurement of nuclear magnetic resonance relaxation times provides a powerful method for the investigation of atomic motion. These well established techniques have been applied to the study of high ionic mobility in ionic materials. Measurement of relaxation due to the modulation of the nuclear dipolar interaction is well understood and together with complementary measurement of ionic conduction and tracer diffusion can provide good insight into the mechanisms of atomic motion in solids. Nuclei with electric quadrupole moments are also relaxed by fluctuating electric field gradients which can arise from defect motion. The analysis of this mechanism is less well understood but promises to provide more detailed information. An extensive investigation is reported of lithium relaxation in lithium oxide crystals which is used to illustrate the possibilities of ion and defect mobility and equilibrium defect concentration measurement over a wide temperature range. Thermal quenching has been observed to produce an additional relaxation process due to a nonequilibrium defect concentration whose dynamics can be investigated.