Dynamical structure of α-Ag 0.99Cu 0.01I crystal by 63Cu NMR chemical shift, spin–lattice relaxation time and molecular dynamics simulation

Abstract

Solid 63Cu NMR and Molecular Dynamics (MD) methods have been used to investigate the dynamical structure of Ag 0.99Cu 0.01I crystal, through the viewpoint of the chemical shift and the spin–lattice relaxation. In the superionic phase (α-phase), we obtained the temperature variation of the chemical shift as −0.2 ppm/K, and the activation energy of the Cu + ion diffusion as 11 kJ/mol. The temperature dependence of the chemical shift was explained by the calculated chemical shielding surface based on ab initio MO calculation, and by the probability density of Cu + ion estimated by MD simulation. The spin–lattice relaxation was also analyzed by using the MD method in which we assumed two jumping models as the diffusion process of the mobile cations. It is concluded that the temperature dependence of the chemical shift is dominated by the shielding in the vicinity of the 24(h) site, and the observed activation energy is due to the diffusion process of the mobile cations jumping from the 6(b) intrasub-lattice to the nearest-neighbor 6(b) sub-lattice.