Speaker
Description
Internal nuclear magnetic fields in various battery materials have been predicted using density functional theory (DFT) calculations to interpret the $\mu^+$SR results, particularly for identifying the diffusing species responsible for the dynamic behavior observed. In materials where Li$^+$ and Na$^+$ ions are mobile, these cations readily change positions to minimize electrostatic repulsion with the implanted $\mu^+$. As a result, the $\mu^+$ sits at the bottom of a deep potential well, stabilizing itself through a ``self-trapping" effect, making it a stable observer for detecting ion diffusion in battery materials. In contrast, in many metals and oxides, the implanted $\mu^+$ diffuses even at low temperatures. In these materials, the local lattice distortion caused by the implanted $\mu^+$ is relatively small compared to that in battery materials. To assess the stability of the implanted $\mu^+$, we propose a ratio between the measured nuclear magnetic field distribution width ($\Delta^{\rm exp}$) and the DFT-predicted value without lattice relaxation ($\Delta^{\rm min}$), namely, $\Delta^{\rm exp}/\Delta^{\rm min}$, as an indicator of whether cations or $\mu^+$ are diffusing. This indicator provides a comprehensive understanding of the diffusive behavior detected with $\mu^+$SR in various materials, including battery materials, metals, and other oxides.
| juns@triumf.ca | |
| Funding Agency | JSPS KAKENHI Grant Numbers JP18H01863, JP20K21149, and JP23H01840. |
