Multiple frequency spin-lattice relaxation time and conductivity measurements of FIC Li2S+SiS2 glasses
Abstract The glass series Li2S+SiS2 is known to be one of the very best fast Li+ ion-conducting glasses and for this reason, it has provided a unique opportunity to examine both the nuclear spin-lattice relaxation (NSLR) of the 7Li+ cation and the ionic conductivity over wide and overlapping regions of frequency and temperature. Since the decoupling indices for these glasses are so high, a wide temperature range above the NSLR rate maximum (in the frequency-independent regime) can be observed and compared directly to the frequency-independent conductivity. As expected, activation energies compared in this way agree very well and this result is used to resolve the long-standing disagreement that has exissted between conductivity and spin-lattice relaxation rate measurements. The frequency-dependent region of the relaxation has been modeled using both the empirical time-domain Kohlrausch- Williams-Watts function and the Cole-Davidson distribution of relaxation times model. Using a frequency range of 4–40 MHz, the first multiple frequency and simultaneous fit of the NSLR rate, R1, to these functions is provided. Though both functions appear to fit the data well, the KWW function is shown to give the better fit. More important is the result that just as the frequency-dependent conductivity can be fit to a relaxation function over wide ranges of frequency and temperature, so can the NSLR rate.