The lithium‐conducting, rare‐earth halides, Li3MX6 (M = Y, Er; X = Cl, Br), have garnered significantly rising interest recently, as they have been reported to have oxidative stability and high ionic conductivities. However, while a multitude of materials exhibit a superionic conductivity close to 1 mS cm−1, the exact design strategies to further improve the ionic transport properties have not been established yet. Here, the influence of the employed synthesis method of mechanochemical milling, compared to subsequent crystallization routines as well as classic solid‐state syntheses on the structure and resulting transport behavior of Li3ErCl6 and Li3YCl6 are explored. Using a combination of X‐ray diffraction, pair distribution function analysis, density functional theory, and impedance spectroscopy, insights into the average and local structural features that influence the underlying transport are provided. The existence of a cation defect within the structure in which Er/Y are disordered to a new position strongly benefits the transport properties. A synthetically tuned, increasing degree of this disordering leads to a decreasing activation energy and increasing ionic conductivity. This work sheds light on the possible synthesis strategies and helps to systematically understand and further improve the properties of this class of materials.

Colloidal nanoparticles, used for applications from catalysis and energy applications to cosmetics, are typically embedded in matrixes or dispersed in solutions. The entire particle surface, which is where reactions are expected to occur, is thus exposed. Here, we show with x-ray pair distribution function analysis that polar and nonpolar solvents universally restructure around nanoparticles. Layers of enhanced order exist with a thickness influenced by the molecule size and up to 2 nanometers beyond the nanoparticle surface. These results show that the enhanced reactivity of solvated nanoparticles includes a contribution from a solvation shell of the size of the particle itself.

Lithium argyrodite superionic conductors are currently being investigated as solid electrolytes for all-solid-state batteries. Recently, in the lithium argyrodite Li6PS5X (X = Cl, Br, and I), a site-disorder between the anions S2– and X– has been observed, which strongly affects the ionic transport and appears to be a function of the halide present. In this work, we show how such a disorder in Li6PS5Br can be engineered via the synthesis method. By comparing fast cooling (i.e., quenching) to more slowly cooled samples, we find that the anion site-disorder is higher at elevated temperatures, and that fast cooling can be used to kinetically trap the desired disorder, leading to higher ionic conductivities as shown by impedance spectroscopy in combination with ab initio molecular dynamics. Furthermore, we observe that after milling, a crystalline lithium argyrodite can be obtained within 1 min of heat treatment. This rapid crystallization highlights the reactive nature of mechanical milling and shows that long reaction times with high energy consumption are not needed in this class of materials. The fact that site-disorder induced via quenching is beneficial for ionic transport provides an additional approach for the optimization and design of lithium superionic conductors.

Driven by the rising demand for consumer electronics, the field of all solid-state batteries employing solid electrolytes as the ion-conducting separator has attracted enormous attention in the last years. Recently, the lithium-conducting rare-earth halides A 3 MX 6 (A = Li, M = Y, Er, X = Cl, Br, I) and Li 3 InX 6 have been rediscovered as potential solid electrolytes, showing a good overall electrochemical performance, while the corresponding sodium-based compounds have been mostly overlooked yet. Here, we report the ionic transport properties of the Na-ion conducting rare-earth halide solid electrolyte Na 3−x Er 1−x Zr x Cl 6 . Na 3−x Er 1−x Zr x Cl 6 shows a conductivity enhancement from 10 −9 S•cm −1 up to of ∼0.04 mS•cm −1 for Na 2.4 Er 0.4 Zr 0.6 Cl 6 , alongside interesting local structural rearrangements of the polyhedral motifs along the series of solid solutions. This series of halide-based sodium-ion conductors sheds light on promising compositions in search for superionic materials.

Nanoparticles in solution interact with their surroundings via hydration shells. Although the structure of these shells is used to explain nanoscopic properties, experimental structural insight is still missing. Here we show how to access the hydration shell structures around colloidal nanoparticles in scattering experiments. For this, we synthesize variably functionalized magnetic iron oxide nanoparticle dispersions. Irrespective of the capping agent, we identify three distinct interatomic distances within 2.5 Å from the particle surface which belong to dissociatively and molecularly adsorbed water molecules, based on theoretical predictions. A weaker restructured hydration shell extends up to 15 Å. Our results show that the crystal structure dictates the hydration shell structure. Surprisingly, facets of 7 and 15 nm particles behave like planar surfaces. These findings bridge the large gap between spectroscopic studies on hydrogen bond networks and theoretical advances in solvation science.