Rapid Li Ion Dynamics in the Interfacial Regions of Nanocrystalline Solids

Abstract

Diffusive processes are ubiquitous in nature. In solid state physics, metallurgy and materials science the diffusivity of ions govern the functionality of many devices such as sensors or batteries. Motional processes on surfaces, across interfaces or through membranes can be quite different to that in the bulk. A direct, quantitative description of such local diffusion processes is, however, rare. Here, we took advantage of Li longitudinal nuclear magnetic relaxation to study, on the atomic length scale, the diffusive motion of lithium spins in the interfacial regions of nanocrystalline, orthorhombic LiBH. Magnetization transients and free induction decays revealed a fast subset of Li ions having access to surface pathways that offer activation barriers (0.18 eV) much lower than those in the crystalline bulk regions (0.55 eV). These observations make orthorhombic borohydride a new nanostructured model system to study disorder-induced enhancements in interfacial diffusion processes.

Spatial confinement – rapid 2D F−diffusion in micro- and nanocrystalline RbSn2F5

“…In such a sample, NMR relaxation measurements clearly revealed a subset of rapidly diffusing Li ions. 93 Here, the nanocrystalline form of RbSn 2 F 5 does not reveal strongly enhanced ion dynamics as compared to the annealed material with sharpened X-ray reflections. Conductivity spectroscopy clearly shows that ionic conductivities are the same for the two morphologies.…”

Lithium-Ion Transport in Nanocrystalline Spinel-Type Li[InxLiy]Br4 as Seen by Conductivity Spectroscopy and NMR

“…Of course, the latter holds only for single crystals or polycrystalline materials with crystallites that show diameters in the µm range. For nanocrystalline samples, the ions residing in the large volume fraction of interfacial regions can be, simultaneously with those in the bulk regions, visualized by NMR (Wilkening et al, 2003;Breuer et al, 2018b). Here, we recorded diffusion-induced 7 Li SLR rates, in both the laboratory and rotating frame of reference, as a function of the inverse temperature (233-393 K) (Heitjans et al, 2005).…”

“…are characterized by very small values of E a ≈ 0.1 eV. Thus, they seem to sample localized ionic motions, which could also originate from Li spins in the interfacial regions (Wilkening et al, 2003;Breuer et al, 2018b) of nanocrystalline Li[In x Li y ]Br 4 . Note that at above 313 K, the Arrhenius line of σ dc T reveals a kink.…”

“…At T = 295 K, the area under the narrow line amounts to about 15%, showing that only a fraction of the available Li spins participate in rapid ion exchange. As for other nanocrystalline ceramics, one might attribute this fraction to those spins residing in the structurally disordered interfacial regions (Wilkening et al, 2003;Breuer et al, 2018b) of nanocrystalline Li[In x Li y ]Br 4 . At elevated T, the whole line is affected by motional narrowing.…”

Under Pressure: Mechanochemical Effects on Structure and Ion Conduction in the Sodium-Ion Solid Electrolyte Na3PS4

“…However, the effect of mechanochemistry to produce highly conducting solid electrolytes remains poorly understood. Multiple hypotheses have been proposed including atomic-scale changes in crystal structure and/or in point defect concentrations, microstructural effects (such as grain boundaries), as well as mesostructural parameters such as particle size/shape and associated surface effects 18,22,23 . Both simulations and experiments show that introducing sodium ion defects through aliovalent doping can decisively enhance ion-transport in Na3PS4 9,11,13,[24][25][26][27][28][29][30] .…”