NMR Study on Li^+ Ionic Motion in Li_xV_2O_5 (0.4≦x≦1.4)(Condensed matter: structure and mechanical and thermal properties)

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The temperature dependences of the ^7Li NMR line width Δv and spin-lattice relaxation rate 1/T_1 have been measured in lithium vanadium bronze Li_xV_2O_5 with 0.4≦x≦1.4 over the temperature range of 77-550K. The narrowing of Δv has been observed for each sample, which is interpreted in terms of the motional narrowing due to the Li^+ ionic diffusion. In Li_<0.8>V_2O_5 with a single δ-phase, an activation energy E_m for the hopping of Li^+ ions is estimated to be 0.16±0.05eV, whereas in Li_<0.4>V_2O_5 the value of 0.10±0.05eV is deduced for the β-phase. The ionic conductivity σ evaluated from the diffusion coefficient D in Li_<0.8>V_2O_5 at 400K is 6.3×10^<-7>Ω^<-1>cm^<-1>, which is consistent with the reported value of σ_<dc>≃10^<-7>Ω^<-1>cm^<-1>. Below 300K, 1/T_1 is considered to be due to magnetic interaction of ^7Li nuclear spins with V^<4+> electronic spins. Above 350K, 1/T_1 is dominated by Li^+ ionic diffusion, from which E_m is estimated to be 0.10±0.05eV.
社団法人日本物理学会の論文
2008-02-15