20227-31-0Relevant academic research and scientific papers
6Li and 7Li MAS NMR studies on fast ionic conducting spinel-type Li2MgCl4, Li2-xCuxMgCl4, Li2-xNaxMgCl4, and Li2ZnCl4
Nagel,Gross,Guenther,Lutz
, p. 303 - 311 (2002)
6Li and 7Li MAS NMR spectra including 1D-EXSY (exchange spectroscopy) and inversion recovery experiments of fast ionic conducting Li2MgCl4, Li2-xCuxMgCl4, Li2-xNaxMgCl4, and Li2ZnCl4 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 Li2-xMxIMgCl4 (MI = Cu, Na) with the copper ions solely at tetrahedral sites and sodium ions at octahedral sites and the normal spinel-type zinc compound, respectively, confirm the assignment of the low-field signal to Litet of inverse spinel-type Li2MgCl4 and the high-field signal to Lioct as proposed by Nagel et al. (2000). In contrast to spinel-type Li2-2xMg1+xCl4 solid solutions with clustering of the vacancies and Mg2+ 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 Ea = 6.6-6.9 and ΔG* > 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 T1 and the correlation times τC of Litet, reveals a dynamic process for the Litet ions inside the tetrahedral voids of the structure, probably between fourfold 32e split sites around the tetrahedral 8a site.
