Magnetic-Resonance Studies of Lithium Vanadium Bronze

Abstract

The nuclear magnetic resonance of Li7 in LixV2O5 shows no Knight shift, but there is a small diamagnetic shift relative to LiCl solution, amounting to 0.0023 and 0.0058% at 296° and 77°K, respectively. The spin—lattice relaxation time T1 as measured by pulse experiments, decreases from 0.16 sec at 296°K to a minimum of 0.060 sec at 163°K and then rises to 0.13 sec at 77°K. The free-induction decay half-width decreases from 850 μsec at 296°K to 100 μsec at 77°K. The minimum in T1 is attributed to back-and-forth motion of the lithium ions within but normal to the axis of channels in the oxygen framework; the line narrowing, to diffusion along the channel from one unit cell to an adjacent one. EPR studies give Lorentzian-shaped lines, centered at g=1.96, of intensity proportional to 1/T. Results are consistent with a model in which lithium atoms in a host V2O5 structure are completely ionized to give Li+ ions and electrons which are almost, but not completely, localized as V4+ centers.