Heterogeneous 7Li NMR relaxation in nanocrystalline Li2O:B2O3 composites

Abstract Nanocrystalline materials can be regarded as heterogeneously structured materials with crystalline grains and disordered interfacial regions. This was verified unambiguously for nanocrystalline Li 2 O using NMR measurements. The heterogeneous structure shows up in the 7 Li NMR line shapes and it results in a heterogeneous dynamic behavior of the Li ions with immobile ions in the grains and mobile ions in the interfacial regions leading to non-exponential recovery of the overall 7 Li magnetization. The two different 7 Li spin reservoirs can be discriminated via their different spin–spin relaxation rates T 2 −1 as well as their different spin-lattice relaxation rates T 1 −1 . The biexponential relaxation behavior becomes more pronounced in the composite material Li 2 O:B 2 O 3 where the volume fraction of interfacial regions and thus the number fraction of fast Li ions is enhanced.