NUCLEAR-SPIN RELAXATION AND ELECTRICAL-CONDUCTIVITY IN LITHIUM GERMANATE GLASSES

Li-7 nuclear spin relaxation (NSR) in the laboratory frame (T1) as well as in the rotating frame (T1g) and electrical conductivity measurements were performed in (1-x) GeO2.xLi2O glass series, where x = 0.001 to 0.36, between 3 K and the glass transition temperature (congruent-to 700 K). Below about 250 K the NSR data can be interpreted consistently in the framework of thermally activated low-frequency excitations of disordered modes intrinsic to the glassy state of matter. The modes are described by asymmetric double well potential (ADWP) configurations with suitable densities of states. Above about 250 K the NSR rates increase exponentially with rising temperature due to diffusive jumps of the Li ions. Deduction of corresponding transport properties, however, from such data by means of standard NSR theories turns out to be difficult. Models are discussed to overcome these difficulties by relating NSR with electrical conductivity. The results are found to correspond best with Funke's model of a coupled motion of the ions caused by Coulomb interaction.