Lithium (6Li and 7Li) NMR in high-temperature phases of lithium vanadium oxide bronzes (LixV2O5; 0.2 .ltoreq. x .ltoreq. 1)

Abstract

A series of high-temperature phases of Li[sub x]V[sub 2]O[sub 5] bronzes (0.2 [<=] x [<=] 1) has been studied by [sup 6]Li and [sup 7]Li NMR. Static spin-echo and MAS NMR experiments have been carried out at two magnetic field strengths (4.7 and 7.1 T). It is shown that the MAS technique permits a very accurate direct determination of the lithium site occupancies in the different phases. The spectra are influenced by interactions from both the quadrupole coupling and the paramagnetic shift due to the dipole interactions of the Li nuclear moment with the paramagnetic vanadium ion moments. Both the magnitudes and relative orientation of the quadrupole (Q) and anisotropic shift (S) tensors have been determined by iterative fitting of the [sup 6]Li and [sup 7]Li MAS NMR line shapes at the two magnetic field strengths. The large difference between the [sup 6]Li and [sup 7]Li quadrupole moments is found to be particularly useful for an accurate determination of the NMR interaction parameters. Calculations of the quadrupole and paramagnetic shift coupling parameters have been performed by using a point monopole and point dipole model, respectively. 54 refs., 9 figs., 3 tabs.