109Ag NMR and relaxation mechanism in single crystal Ag β-alumina

Temperature dependence of 109Ag NMR spectrum and spin-lattice relaxation T1 was measured for a single crystal of Ag β-alumina (Ag1.17Al11O17.09) at external magnetic field of 4.7 T (9.3 MHz) and 9.4 T (18.6 MHz).Only a single spectrum peak is observed at room temperature, it reflects fast site exchange of Ag ions. The chemical shift of the peak position depends on the angle between c-axis and external field B0. From the angle dependence, the values of screening tensor are determined to be, σxxPAS = σyyPAS = − 54.7 ppm, σzzPAS = − 212 ppm. The large difference between σzzPAS and σxxPAS indicates a strong interaction between Ag and surrounding oxygen.The relaxation mechanism is discussed using the Scalar Coupling (SC) model and Screening Tensor Fluctuation (STF) model. The field dependence of the T1 observed at 4.7 T and 9.4 T strongly supports the SC model. It suggests that there are strong correlations between Ag ions in β-alumina and it probably plays an important role to the high ionic conductivity.