A NUCLEAR-SPIN-LATTICE RELAXATION STUDY OF THE MIXED-ALKALI EFFECT IN GLASSES

The Li-7 nuclear spin-lattice relaxation time has been measured as a function of temperature for a series of mixed-alkali Li-Na disilicate glasses. No evidence of a pronounced non-linear mixed-alkali effect was found for the low-temperature activation energy, E(LT), of the spin-lattice relaxation (SLR) rate, nor of the ratio E(LT)/E(sigma) (where E(sigma) is the dc conductivity activation energy). These results can be interpreted, in terms of Elliott and Owens' diffusion-controlled relaxation model for SLR, as indicating that there is no significant change in the number of mobile ions in mixed-alkali glasses; instead, the mixed-alkali effect must be due to changes in the ionic mobility.