DEDICATED TO PROFESSOR DR. MARIANNE BAUDLER ON THE OCCASION OF HER 80TH BIRTHDAY 6 Li and 7 Li MAS NMR spectra including 1D-EXSY (exchange spectroscopy) and inversion recovery experiments of fast ionic conducting Li 2 MgCl 4 , Li 2+x Cu x MgCl 4 , Li 2+x Na x MgCl 4 , and Li 2 ZnCl 4 have been recorded and discussed with respect to the dynamics and local structure of the lithium ions. The chemical shifts, intensities, and half-widths of the Li MAS NMR signals of the inverse spinel-type solid solutions Li 2+x M I
x MgCl 4 (M I ؍ Cu, Na) with the copper ions solely at tetrahedral sites and sodium ions at octahedral sites and the normal spinel-type zinc compound, respectively, con5rm the assignment of the low-5eld signal to Li tet of inverse spinel-type Li 2 MgCl 4 and the high-5eld signal to Li oct as proposed by Nagel et al. (2000). In contrast to spinel-type Li 2+2x Mg 1؉x Cl 4 solid solutions with clustering of the vacancies and Mg 2؉ ions, the Cu ؉ and Na ؉ ions are randomly distributed on the tetrahedral and octahedral sites, respectively. The activation energies due to the various dynamic processes of the lithium ions in inverse spinel-type chlorides obtained by the NMR experiments are E a ؍ 6.6+6.9 and G* > 79 kJ mol +1 (in addition to 23, 29, and 75 kJ mol +1 obtained by other techniques), respectively. The largest activation energy of >79 kJ mol +1 corresponds to hopping exchange processes of Li ions between the tetrahedral 8a sites and the octahedral 16d sites. The smallest value of 6.6+6.9 kJ mol +1 , which was derived from the temperature dependence of both the spin-lattice relaxation times T 1 and the correlation times C of Li tet , reveals a dynamic process for the Li tet ions inside the tetrahedral voids of the structure, probably between fourfold 32e split sites around the tetrahedral 8a site.
2002 Elsevier Science (USA)