6Li and 7Li MAS NMR Studies on Fast Ionic Conducting Spinel-Type Li2MgCl4, Li2–xCuxMgCl4, Li2–xNaxMgCl4, and Li2ZnCl4
| Autor: | H.D. Lutz, R. Nagel, Th.W. Groß, H. Günther |
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| Rok vydání: | 2002 |
| Předmět: |
Magic angle
Inorganic chemistry chemistry.chemical_element Ionic bonding Nuclear magnetic resonance spectroscopy Condensed Matter Physics Electronic Optical and Magnetic Materials Ion Inorganic Chemistry Crystallography chemistry Octahedron Materials Chemistry Ceramics and Composites Ionic conductivity Lithium Physical and Theoretical Chemistry Solid solution |
| Zdroj: | Journal of Solid State Chemistry. 165:303-311 |
| ISSN: | 0022-4596 |
| DOI: | 10.1006/jssc.2002.9534 |
| Popis: | 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, confirm the assignment of the low-field signal to Li tet of inverse spinel-type Li 2 MgCl 4 and the high-field signal to Lioct as proposed by Nagel et al. (2000). In contrast to spinel-type Li 2–2 x 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 Δ G * >79 KJ mol −1 (in addition to 23, 29, and 75 kJmol–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 8 a sites and the octahedral 16 d 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 τ C of Li tet , reveals a dynamic process for the Li tet ions inside the tetrahedral voids of the structure, probably between fourfold 32 e split sites around the tetrahedral 8 a site. |
| Databáze: | OpenAIRE |
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