Lithium diffusion in LiMnPO_{4} detected with μ^{±}SR

Abstract

Positive- and negative-muon spin rotation and relaxation (μ^{±}SR) was first used to investigate fluctuations of nuclear magnetic fields in an olivine-type battery material, LiMnPO_{4}, in order to clarify the diffusive species, namely, to distinguish between a μ^{+} hopping among interstitial sites and Li^{+} ions diffusing in the LiMnPO_{4} lattice. Muon diffusion can only occur in μ^{+}SR, because the implanted μ^{−} forms a stable muonic atom at the lattice site, and therefore any change in linewidth measured with μ^{−}SR must be due to Li^{+} diffusion. Since the two measurements exhibit a similar increase in the field fluctuation rate with temperature above 100 K, it is confirmed that Li^{+} ions are in fact diffusing. The diffusion coefficient of Li^{+} at 300 K and its activation energy were estimated to be 1.4(3)×10^{−10}cm^{2}/s and 0.19(3) eV, respectively. Such combined μ^{±}SR measurements are thus shown to be a suitable tool for detecting ion diffusion in solid-state energy materials.