Nuclear magnetic resonance study of dynamics in oxide glasses above the glass-transition temperature

Abstract

Nuclear magnetic resonance experiments on glasses of the AgI, Ag₂O, B₂O₃ system are reported. We discuss the spin-lattice relaxation time T₁ of boron atoms (¹¹B) tetrahedrally coordinated to oxygen atoms above the glass-transition temperature T _g. As expected, structural relaxation within the borate network becomes the main mechanism of spin-lattice relaxation at ∼ 150 K above T _g. On the other hand, ∼ 50 K above T _g the ¹¹B spin-lattice relaxation rates increase rapidly with temperature and become independent of frequency. This behaviour is anomalous, since it implies that the dynamics involved in the spin-lattice relaxation process cannot be described in terms of a temperature-activated correlation time. Microscopic interpretations are presented which point to the collective vibration-like character of the motion responsible for the anomalous ¹¹B spin-lattice relaxation.