NMR Study on Li⁺ Ionic Motion in Li_xV₂O₅ (0.4≤x≤1.4)

抄録

The temperature dependences of the ⁷Li NMR line width Δν and spin–lattice relaxation rate 1⁄T₁ have been measured in lithium vanadium bronze Li_xV₂O₅ with 0.4≤x≤1.4 over the temperature range of 77–550 K. The narrowing of Δν has been observed for each sample, which is interpreted in terms of the motional narrowing due to the Li⁺ ionic diffusion. In Li_0.8V₂O₅ with a single δ-phase, an activation energy E_m for the hopping of Li⁺ ions is estimated to be 0.16±0.05 eV, whereas in Li_0.4V₂O₅ the value of 0.10±0.05 eV is deduced for the β-phase. The ionic conductivity σ evaluated from the diffusion coefficient D in Li_0.8V₂O₅ at 400 K is 6.3×10⁻⁷ Ω⁻¹ cm⁻¹, which is consistent with the reported value of σ_dc\\simeq10⁻⁷ Ω⁻¹ cm⁻¹. Below 300 K, 1⁄T₁ is considered to be due to magnetic interaction of ⁷Li nuclear spins with V⁴⁺ electronic spins. Above 350 K, 1⁄T₁ is dominated by Li⁺ ionic diffusion, from which E_m is estimated to be 0.10±0.05 eV.