Frequency-dependent spin-lattice relaxation study of transport processes in superionic conductors

The sensitivity of the F-19 spin-lattice relaxation dispersion, T-1(omega), to motional disorder in crystalline superionic conductors of the type La1- xSrxF3-x (x = 0; 0.03) is shown. T-1 times are measured in the frequency ra nge from 90 kKz to 370 MHz using standard techniques in combination with fi eld-cycling. The relaxation dispersion shows qualitative differences from t he standard Bloembergen-Purcell-Pound behavior. At low frequencies a relaxa tion model using a distribution of correlation times for diffusing ions is found to be consistent with the experimental results. At frequencies higher than 50 MHz another process of the Debye type which is not induced by ioni c hopping dominates the relaxation.