6Li and 7Li MAS-NMR studies on fast ionic conducting inverse spinel-type Li2−2xMg1+xCl4 and normal spinel-type Li2ZnCl4

The 6Li and 7Li MAS-NMR signals of fast ionic conducting Li2−2xMg1+xCl4 have been assigned to the two lithium ion positions of their inverse spinel-type structure. The chemical shift of the two 6Li signals of Li2MgCl4 is 1.2 and 0.3 ppm compared to 6LiCl, that of normal spinel-type 6Li2ZnCl4 is 0.2 ppm. Whereas the relative intensities of the 6Li signals fairly well reflect the occupation factors of the tetrahedral and octahedral sites, the intensities of the 7Li signals strongly deviate from the occupation factors. This is probably caused by distortion of the 7Li signals through quadrupolar interaction. The different chemical shift and halfwidth of the signals are discussed with respect to shielding and dipolar interaction. Their change with increasing magnesium content can be explained by formation of vacancies at the tetrahedral sites on substitution of Li+ by Mg2+ and clustering of the randomly distributed Li+ and Mg2+ ions at the octahedral sites.