Spin relaxation and ultra-slow Li motion in an aluminosilicate glass ceramic

The ion dynamics in a lithium alummosilicate glass ceramic was studied using stimulated-echo Li-7-NMR. For temperatures 300 K < T < 450 K the hopping correlation times, tau(C), were determined from the decay of the quadrupolar spin-alignment amplitude. The decay times were thermally activated with an energy barrier of 0.61 eV, in agreement with conductivity measurements. For T < 300 K the temperature dependence of the decay times, now corresponding to T-1Q, was much weaker. The T-1Q times followed the same trend as the independently measured spin-lattice relaxation times, T-1, but were a factor of about three shorter than those. The theoretical ratio of T-1/T-1Q is shown to be 25/8 in the slow-motion regime if quadrupolar spin relaxation prevails. This result explains the present observation and similar ones made for several Li ion conductors. The relaxation of the octupolar spin-alignment order is discussed. (c) 2006 Elsevier Inc. All rights reserved.