Ion-implanted ⁸Li nuclear magnetic resonance study of van der waals layered materials

This thesis explores the behavior of dilute-limit lithium in different van der Waals layered materials. The rationale for this choice is that their spacious, two-dimensional atomic structure enables their use as good electrode hosts in rechargeable lithium-ion batteries. In order to assist efforts to simulate the mobility (or diffusion) of the lithium from first-principles, we make use of ⁸Li β-detected nuclear magnetic resonance. Here, an isotopically pure beam of ⁸Li is implanted directly into a suitable sample. The ⁸Li are isolated (non-interacting) from one another, a situation that is ideally comparable to theory, in contrast to the more concentrated regime that is dealt with in most other experimental studies of diffusion. By monitoring the asymmetric β-decay of the ⁸Li correlated to its spin polarization, we are sensitive to the temporal evolution of the local magnetic and electric field distribution in the vicinity of the ⁸Li probe as it moves within its crystalline environment. Measurements of the spin-lattice relaxation rate, as well as the resonance linewidth, are then connected to a model of the elementary atomic hopping of the lithium. We apply this in three separate case studies: semimetallic graphite, semiconducting MoX₂ (X = S, Se), and metallic CrSe₂. We find an absence of diffusive mobility of lithium in graphite even to 400 K, marking a clear departure from the more concentrated stage compounds. However, we find quantitative evidence of lithium diffusion in both MoX₂ and CrSe₂ near room temperature. The respective activation energy barriers in each case are closely compared to prior results from theory. Other phenomena (e.g., magnetic effects) that act in parallel to diffusion are also closely examined.