The temperature and frequency dependence of ²⁷Al and ²³Na nuclear-spin relaxation (NSR) has been studied in Na {β}-alumina between about 1.5 and 100 K. Below 50 K the NSR is shown to be caused by low-frequency excitations of disorder modes, which are intrinsic to the glasslike state of {β} aluminas. The data can be interpreted consistently in the framework of thermally activated excitations of modes that are represented by asymmetric double-well-potential configurations with suitably chosen densities of states. Further, the observed NSR rates are shown to be related to corresponding ac-conductivity data via the fluctuation-dissipation theorem.
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Sieranski et al. (1993) studied this question.
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