Diffusion processes in the superionic conductorLi3N: An NMR study

A comprehensive experimental and theoretical NMR study of two diffusion processes in ${\mathrm{Li}}_3$N is presented: interlayer diffusion parallel to the hexagonal axis involving both Li sites and intralayer diffusion within the ${\mathrm{Li}}_2$N layers only. The first process allows a quantitative and consistent analysis of the following NMR observables: (i) the second-order quadrupolar shift of the ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$ central signal and its strong temperature dependence between 400 and 600 K, and (ii) the temperature dependence (above 420 K) and the extreme angle dependence of the ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$ and ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ relaxation rates by taking into account different relaxation mechanisms for both isotopes. The activation energy (0.62 eV) and the correlation times agree with values deduced from conductivity measurements. The intralayer diffusion process is studied by means of the temperature and angle dependence of ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ and ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$ relaxation times below 320 K. The Li(2) vacancy concentration is determined in agreement with x-ray data.