On-Line Diffusion Tracing in Li Ionic Conductors by the Short-Lived Radioactive Beam of ⁸Li

Abstract

A non-destructive and on-line diffusion tracing in Li ionic conductors has been demonstrated. As the tracer, the pulsed beam of the short-lived -emitting radioisotope of 8 Li was implanted into a typical Li ionic conductor LiGa. By analyzing the timedependent yields of the -particles measured in coincident with the repetition cycle of the beam, the tracer diffusion coefficients were extracted with a good accuracy. The ordering of the Li vacancies in the Li-deficient phase of LiGa was observed for the first time in terms of the Li diffusion by the present method.

Slow Lithium Transport in Metal Oxides on the Nanoscale

“…Consequently, in literature only some special publications can be found. There are experiments based on the radio tracer method using the prompt alpha-decay following the beta-decay of the short-lived isotope 8 Li (t 1/2 = 0.84 s) [17]. Such elegant experiments are, however, of low significance for slow diffusivities due to the limited annealing time period available.…”

In situ lithium diffusion measurement in solid ionic conductors using short-lived radiotracer beam of 8Li

“…In the present case, however, the inherent energy distribution of the a particles is continuous and broad [7]. Although the correspondence between the emitted position and measured energy of the charged particles is not as simple as above-mentioned, it was shown that the tracer diffusion coefficient could be obtained from the time-dependent yields of a particles emitted by diffusing 8 Li with the help of the simulation [8][9][10]. Fig.…”

“…400 keV in Ref. [9]) were traced with time, allowing to measure diffusion coefficients in Li ionic conductors with an accuracy of about 20% and sensitivity down to 10 À10 cm 2 /s [9]. However, no diffusion effects were observed when applying the method for measuring lithium diffusion coefficients in LiCoO 2 even at the temperature of 573 K (maximum temperature accessible in the experimental set-up used so far, see Fig.…”

“…Then a charged particle detector, located close to the sample surface, could selectively detect a particles from 8 Li diffusing toward the sample surface, since the implantation depth is deeper than the average projected range of a particles in the present case. Therefore, the temporal evolution of a particles yields that come out of the sample would be a measure of the diffusivity of 8 Li [8,9], which is sensitive to the diffusion over the implantation depth during the tracer lifetime, i.e. micrometer scale of 6 lm as shown in Fig.…”

“…Based on the relative time-dependency of a particle yields (time dependent ratios), the diffusion coefficient of lithium in the bulk sample of LVSO at 523 K was obtained to be 2.2 Â 10 À9 cm 2 /s by comparing with the simulations in which one-dimensional Fickian (Gaussian) diffusion was assumed [9]. Extrapolating the measurements to lower temperature, we can expect that the lithium diffusion coefficients in the bulk LVSO are smaller than 10 À10 cm 2 /s at temperatures below 473 K because the detection limit of the micrometer sensitive method is in the order of 10 À10 cm 2 /s.…”