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1. Lithium metal atoms fill vacancies in the germanium network of a type-I clathrate: synthesis and structural characterization of Ba ₈ Li ₅ Ge ₄₁

   https://doi.org/10.1039/D3DT01168B  

   Ghosh, Kowsik; Ovchinnikov, Alexander; Baitinger, Michael; Krnel, Mitja; Burkhardt, Ulrich; Grin, Yuri; Bobev, Svilen (August 2023, Dalton Transactions)

   Clathrate phases with crystal structures exhibiting complex disorder have been the subject of many prior studies. Here we report syntheses, crystal and electronic structure, and chemical bonding analysis of a Li-substituted Ge-based clathrate phase with the refined chemical formula Ba8Li5.0(1)Ge41.0, which is a rare example of ternary clathrate-I where alkali metal atoms substitute framework Ge atoms. Two different synthesis methods to grow single crystals of the new clathrate phase are presented, in addition to the classical approach towards polycrystalline materials by combining pure elements in desired stoichiometric ratios. Structure elucidations for samples from different batches were carried out by single-crystal and powder X-ray diffraction methods. The ternary Ba8Li5.0(1)Ge41.0 phase crystallizes in the cubic type-I clathrate structure (space group no. 223, a  10.80 Å), with the unit cell being substantially larger compared to the binary phase Ba8Ge43 (Ba8□3Ge43, a  10.63 Å). The expansion of the unit cell is the result of the Li atoms filling vacancies and substituting atoms in the Ge framework, with Li and Ge co-occupying one crystallographic (6c) site. As such, the Li atoms are situated in four-fold coordination environment surrounded by equidistant Ge atoms. Analysis of chemical bonding applying the electron density/ electron localizability approach reveals ionic interaction of barium with the Li–Ge framework, while the lithium-germanium bonds are strongly polar covalent. 

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2. Polarization-dependent optical responses in natural 2D layered mineral teallite

   https://doi.org/10.1038/s41598-021-01511-z  

   Tripathi, Ravi P.; Yang, Xiaodong; Gao, Jie (December 2021, Scientific Reports)

   Abstract Multi-element layered materials enable the use of stoichiometric variation to engineer their optical responses at subwavelength scale. In this regard, naturally occurring van der Waals minerals allow us to harness a wide range of chemical compositions, crystal structures and lattice symmetries for layered materials under atomically thin limit. Recently, one type of naturally occurring sulfide mineral, ternary teallite has attained significant interest in the context of thermoelectric, optoelectronic, and photovoltaic applications, but understanding of light-matter interactions in such ternary teallite crystals is scarcely available. Herein, polarization-dependent linear and nonlinear optical responses in mechanically exfoliated teallite crystals are investigated including anisotropic Raman modes, wavelength-dependent linear dichroism, optical band gap evolution, and anisotropic third-harmonic generation (THG). Furthermore, the third-order nonlinear susceptibility of teallite crystal is estimated using the thickness-dependent THG emission process. We anticipate that our findings will open the avenue to a better understanding of the tailored light-matter interactions in complex multi-element layered materials and their implications in optical sensors, frequency modulators, integrated photonic circuits, and other nonlinear signal processing applications. 

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3. Exploring the Electronic Dimensionality of Ternary and Quaternary Rhodium Halides

   https://doi.org/10.1021/acs.chemmater.3c03208  

   Liu, David; Holzapfel, Noah P.; Milder, Alexander; Woodward, Patrick M. (March 2024, Chemistry of Materials)

   The synthesis, crystal structures, and optical properties of four ternary and six quaternary halides containing the Rh3+ ion are reported here. Rb3RhCl6 adopts a monoclinic structure with isolated [RhCl6]3− octahedra. Rb3Rh2Cl9, Cs3Rh2Cl9, and Cs3Rh2Br9 crystallize in a vacancy ordered variant of the 6H hexagonal perovskite structure, which contains isolated Rh2X93− (X = Cl, Br) dimers of face-sharing octahedra. Cs2AgRhCl6 and Cs2NaRhCl6 adopt the 12R rhombohedral perovskite structure, featuring [M2RhCl12]7− face-sharing octahedral trimers, connected to one another through rhodium-centered octahedra. A4AgRhCl8 and A4AgRhBr8 (A = CH3CH2CH2CH2NH3+, (CH3)2CHCH2CH2NH3)+) crystallize in a cation-ordered variant of the n = 1 Ruddlesden Popper structure, which features layers of corner-connected octahedra with a chessboard ordering of Ag+ and Rh3+ ions separated by double layers of organic cations. The diffuse reflectance spectra of all compositions studied feature peaks in the visible that can be attributed to spin-allowed d-to-d transitions and peaks in the UV that arise from charge transfer transitions. Electronic structure calculations reveal moderate Rh–X–Ag hybridization when rhodium- and silver-centered octahedra share corners, but minimal hybridization when they share faces. Many of the compositions studied have an electronic structure that is effectively zero-dimensional, but Cs2AgRhCl6 is found to possess a two-dimensional electronic structure. The results are instructive for controlling the electronic dimensionality of compositionally complex halide perovskite derivatives. 

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4. Insights into Lithium Sulfide Glass Electrolyte Structures and Ionic Conductivity via Machine Learning Force Field Simulations

   https://doi.org/10.1021/acsami.4c00618  

   Zhou, Rui; Luo, Kun; Martin, Steve W; An, Qi (April 2024, ACS Applied Materials & Interfaces)

   Sulfide-based solid electrolytes (SEs) are emerging as compelling materials for all-solid-state batteries (ASSBs), primarily due to their high ionic conductivities and robust mechanical stability. In particular, glassy SEs (GSEs) comprising mixed Si and P glassformers show promise, thanks to their efficient synthesis process and their intrinsic ability to prevent lithium dendrite growth. However, to date the complexity of their glassy structures hinders a complete understanding of the relationships between their structures and properties. Here, new machine learning force field (ML- FF) specifically designed for lithium sulfide-based GSEs has been developed. This ML-FF has been used to investigate the structural characteristics, mechanical properties, and lithium ionic conductivities in binary lithium thiosilicate and lithium thiophosphate GSEs, as well as their ternary mixed glassformer (MGF) lithium thiosilicophosphate GSEs. Molecular dynamic (MD) simulations using the ML-FF were conducted to explore the glass structures in varying compositions, including binary Li2S-SiS2 and Li2S-P2S5, as well as ternary Li2S-SiS2-P2S5. The simulations with the ML-FF yielded consistent results in terms of density, elastic modulus, radial distribution functions, and neutron structure factors, compared to DFT and experimental work. A key focus of this study was to investigate the local environments of Si and P molecular clusters. We discovered that most Si atoms in the Li2S-SiS2 GSE are situated in an edge-sharing environment, while the Li2S-P2S5 glass contained a minor proportion of edge-sharing P2S62- environments. In the ternary 60Li2S-32SiS2-8P2S5 glass, the ML-FF predicted similar P environments as observed in the binary Li2S-P2S5 glass. Additionally, it indicated the coexistence of corner and edge-sharing between PS4 and SiS4 tetrahedra in this ternary composition. Concerning lithium ionic conductivity at 300K, all studied glass compositions exhibited similar magnitudes and followed the Arrhenius relationship. The 50Li2S-50SiS2 glass displayed the lowest conductivity at 2.1 mS/cm, while the 75Li2S-25P2S5 composition exhibited the highest at 3.6 2 mS/cm. The ternary glass showed a conductivity of 2.57 mS/cm, sitting between the two. Interestingly, the predicted conductivities were about an order of magnitude higher than experimental values for the binary glasses but aligning more closely with that of the ternary glass. Moreover, an in-depth analysis of lithium-ion diffusion over the MD trajectory in the ternary glass demonstrated a significant correlation between diffusion pathways and the rotational dynamics of nearby SiS4 or PS4 tetrahedra. The ML-FF developed in this study shows immense potential as a versatile tool for exploring a broad spectrum of solid-state and mixed-former sulfide-based electrolytes. 

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5. Multifaceted Sn–Sn bonding in the solid state. Synthesis and structural characterization of four new Ca–Li–Sn compounds

   https://doi.org/10.1039/C9DT02803J  

   Ovchinnikov, Alexander; Bobev, Svilen (October 2019, Dalton Transactions)

   null (Ed.)

   Four novel ternary phases have been prepared in the system Ca–Li–Sn using both the metal flux method and conventional high-temperature synthesis. Each of the obtained compositions represents its own (new) structure type, and the structures feature distinct polyanionic Sn units. Ca 4 LiSn 6 (space group Pbcm , Pearson symbol oP 44) accommodates infinite chains, made up of cyclopentane-like [Sn 5 ]-rings, which are bridged by Sn atoms. The Sn atoms in this structure are two- and three-bonded. The anionic substructure of Ca 9 Li 6+x Sn 13–x ( x ≈ 0.28, space group C 2/ m , Pearson symbol mS 56) displays extensive mixing of Li and Sn and combination of single-bonded and hypervalent interactions between the Sn atoms. Hypervalent bonding is also pronounced in the structure of the third compound, Ca 2 LiSn 3 (space group Pmm 2, Pearson symbol oP 18) with quasi-two-dimensional polyanionic subunits and a variety of coordination environments of the Sn atoms. One-dimensional [Sn 10 ]-chains with an intricate topology of cis - and trans -Sn–Sn bonds exist in the structure of Ca 9–x Li 2 Sn 10 ( x ≈ 0.16, space group C 2/ m , Pearson symbol mS 42), and the Sn–Sn bonding in this case demonstrates the characteristics of an intermediate between single- and double- bond-order. The peculiarities of the bonding are discussed in the context of the Zintl approach, which captures the essence of the main chemical interactions. The electronic structures of all four compounds have also been analyzed in full detail using first-principles calculations. 

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