Frequency dependence of spin-lattice relaxation of 27Al in one-dimensional ionic conductor, priderites

Temperature and frequency dependences of T-1* of Al-27 in K-Al- and Rb-Al-priderite were measured at three frequencies of 20.8, 104.2 and 130.3 MHz in the temperature range from 20 K to 909 K. The temperature dependence of K-Al-priderite is divided into three regions: region 1 below 30 K, region 2 from 30 K to 170 K where T-1* is dominated by the ionic motion over the intrinsic barriers, and region 3 above 170 K where T-1* is dominated by the ionic motion over the impurity barriers. The temperature and frequency dependence of T-1* in the region 2 is well described by a trial function of J(omega,tau) which has the T-1* proportional to omega(1.0) dependence in the low temperature limit. But in the case of Rb-Al-priderite, the frequency dependence measured in a temperature range which corresponds to the region 2 of K-Al-priderite showed an intermediate dependence between omega(1.5) and omega(2) dependence. These frequency dependences are compared with Ishii's calculation result of S(omega) of hopping ions in one-dimensional random lattice based on his relaxation mode theory. E-NMR obtained from the slope of the straight line in the log(T-1*) vs. 1/T plot in the region 2 of both samples showed a tendency that E-NMR measured at low frequency has a little smaller value. It means that ENMR is dependent on the frequency.