Ion Jump Motion as the Background for Muon Diffusion in Battery Materials Research Using μ SR

Numerical simulations of muon spin relaxation (μSR) in ion diffusion were performed using the extended Kubo-Toyabe (KT) relaxation function Gᵦ^ EA (t) that incorporates an Edwards-Anderson type autocorrelation function for the jump motion of ions. The analysis of the generated μSR spectra using the conventional KT function Gᵦ^ KT (t;Δ ₊ₓ, ν ₊ₓ) (mimicking the previous analysis procedure) suggest that the anomalous peak in the fluctuation rate ν ₊ₓ around a specific temperature T^* and associated decrease of the linewidth Δ ₊ₓ above T^*, often observed in the previous μSR studies on ion diffusion, originate from the sharp increase in the ion jump rate ν ₈ against that of the muon ν_μ with increasing temperature. This indicates that a more detailed reanalysis of the vintage data using Gᵦ^ EA (t) is useful for the proper evaluation of ν ₈ and ν_μ. Meanwhile, it also suggests that the μSR results showing no such anomaly convey little information on ion diffusion.