LOW-TEMPERATURE DYNAMICS OF INORGANIC GLASSES - ELECTRICAL-CONDUCTIVITY AGAINST NUCLEAR-SPIN RELAXATION

At low temperatures, nuclear spin relaxation (NSR) can be related to e lectrical conductivity in various inorganic oxide glasses by the fluct uation-dissipation theorem. The results indicate a common physical ori gin of the relaxation mechanism owing to fluctuating charges. In compa rison, however, in heavy metal fluoride glasses, NSR is shown to detec t additional fluctuations which are not observed by conductivity exper iments. The underlying relaxation process is caused by nuclear magneti c fluctuations without any accompanying charge motions. Both dielectri c and NSR responses can be explained in terms of thermally activated e xcitations of asymmetric double-well potential (ADWP) configurations i ntrinsic to highly disordered solids. The ADWP configurations are char acterized from the effect of alkali concentration and size on the low- temperature conductivity. The asymmetry of ADWP configurations is dete rmined primarily by the elastic strains in the structure.