A quantitative explanation of the difference between nuclear spin relaxation and ionic conductivity relaxation in superionic glasses

Abstract

Electrical conductivity relaxation (ECR) experimental data represented by either the complex conductivity or the complex electric modulus are macroscopic in nature. In contrast to ECR, nuclear spin relaxation is a more direct probe of ionic movement and from its result we can infer the microscopic dynamics of the ions. Combined studies of ionic motion using ECR and nuclear spin-lattice relaxation (SLR) in several glassy ionic conductors have shown a large difference between the ECR and SLR times. Any theory that attempts to explain quantitatively the difference faces the dilemma of how to compare the SLR time with the ECR time. In this work we use a recent result [Phys. Rev. B 60 (1999) 9396] to find the ion hopping correlation time from the experimental ECR time. Next, we use the coupling model to calculate the SLR time from the ion hopping correlation time. Good agreements are obtained in three glassy ionic conductors and a crystalline ionic conductor.