Effects of disorder on electron-spin relaxation inβ-alumina: A prototype glass

Properties unique to disordered materials have been observed through electron paramagnetic resonance studies of a prototype glass. The electron-spin-relaxation rate of an irradiation-induced color center was measured in K, Li, and Na $\beta$-alumina, and revealed expectionally fast relaxation with anomalous temperature and microwave frequency dependence. This behavior is quantitatively described by a mechanism involving the coupling of a color center to the phonon-induced relaxation of a nearby localized two-level tunneling state. A detailed comparison shows that our model is in agreement with earlier heat-capacity, thermal-conductivity, and dielectric-susceptibility measurements in $\beta$-alumina.