Clathrate Structure Research Articles

Impact of laponite on the formation of NGHs and its adaptability for use in NGH drilling fluids

Natural gas hydrates (NGHs) are important potential alternative energy sources of oil and gas, which are efficient and clean. Their exploration and development are inseparable from drilling and drilling fluids. Adding nanomaterials into drilling fluid can effectively weaken the invasion of the drilling fluid into a formation, which is conducive to safe and efficient drilling. Therefore, this study explores the impact pattern and mechanism of different types and dosages of laponite on the formation of hydrates and analyses the adaptability of laponite in offshore NGH drilling fluids. The results show that the hydration of laponite prevents the directional arrangement of water molecules from forming a clathrate structure, and laponite forms a “house of cards” structure in the aqueous phase, which increases the resistance to mass transfer and inhibits the nucleation and growth of hydrates. Under the action of hydration, laponite planarly adsorbs a certain amount of strongly bound water that fails to participate in the formation of hydrates, thereby reducing the amount of hydrates formed. In addition, laponite basically does not increase the viscosity of drilling fluid at low temperatures but strengthens the inhibition and settling stability of the drilling fluid, significantly improving the comprehensive performance of the drilling fluid. It is concluded that 1.0 wt% laponite-RD is suitable for use in hydrate drilling fluid systems, the induction time was extended to 451.33 min, the methane consumption was reduced to 0.12623 mol, the average methane consumption rate was reduced to 0.23983 × 10−3 mol/min, and the linear expansion rate of sediments is as low as 10.2%, which shows excellent rheological property and sedimentation stability.

A Clathrate Hydrate Structure Hidden in Plain Sight.

Clathrate hydrates have diverse crystal structures, and among them, the three (sI, sII, and sH) most prevalent ones cover nearly all known structures, while the norm is to consider other structures only when specific guest molecules are present. Here we report the observation of a hidden clathrate structure: the tetragonal structure (TS-I) in commonly formed gas hydrates, as evidenced from molecular dynamics simulations. We show that when two (or more) sI crystal grains with different growth directions come into contact or when the growth of a sI crystal encounters geometrical frustration, the TS-I results as a cocrystal. We give evidence that TS-I may also play an important role in the combination and/or transition between sI and sII. These results imply that this previously neglected structure may be commonly present whenever sI or sII is formed. This hidden structure must be identified, experimentally and in simulations; confining the possible structures may hinder an in-depth understanding of clathrate hydrates.

Observation of mesoscopic clathrate structures in ethanol-water mixtures

Alcohol in water is one of the fundamental liquid–liquid solutions in chemical and biological processes. Water-alcohol mixtures exhibit many abnormal physicochemical properties, the origins of which remain mysterious. In addition, the presence of a high concentration of mesoscale objects in such mixtures has caused debate; many researchers attribute these objects to bulk nanobubbles because their concentration is strongly affected by the amount of dissolved air gases. To resolve these issues, here we use transmission electron microscopy (TEM), nanoparticle tracking analysis (NTA), and atomic force microscopy (AFM) to study ethanol–water mixtures. TEM reveals mesoscopic clathrate structures with water molecules forming a crystalline matrix hosting a high density of tiny cells. The presence of these mesoscopic clathrate structures is further supported by a refractive index of 1.27 ± 0.02 at 405 nm measured via NTA and the hydrophilic nature of the mesoscopic structures implied by AFM observations, explaining many long-standing puzzles related to water-alcohol mixtures.

Structural and spectroscopic studies of Na+ – Quercetin-5′-sulfonic acid polymeric complexes obtained via solvothermal synthesis

New sodium complexes of quercetin-5′-sulfonic acid (HQSA) have been obtained. The aqua complex of the general formula [NaQSA∙(H2O)2]·2H2O (1) was a starting compound for solvothermal syntheses of acetone and dimethylsulfoxide (S) complexes: [NaQSA(S)](S) (2 – acetone) and [NaQSA(S)]∙2(S) (3a and 3b – DMSO). The fourth complex obtained from the reaction of HQSA excess used in the reaction with NaOH is [Na(QSA)2·2H2O][(EtOH)2H] (4). The molecular and crystal structures of 1 – 4 were determined by X-ray crystallography. The sodium cations are coordinated by six or seven oxygen atoms; Na+ coordinating groups are sulfonic, hydroxyl, and carbonyl of the QSA− anion. The bridging role of some functional groups causes the formation of polymeric complexes. The coordination spheres are completed by oxygen atoms from the coordinating water (in 1 and 4), acetone (2) or DMSO molecule (3a and 3b). In each structure non-coordinating interstitial solvate molecules are also present; they are two H2O (1), acetone (2), two DMSO (3a and 3b), and the hydrogen bisethanol cation [EtOH…H+…EtOH] (4). The last of these is a rare type of Zundel type cation. Unstable complexes (2 and 3), that decompose under normal conditions, are formed and they have a structure of intercalation clathrates. The solvating molecules, located between 1D or 2D polymeric complexes, play a unique role as a network bonding agent. Theoretical calculations showed charge separation between Na+ and SO3−. The FTIR and Raman spectra are consistent with the solved crystal structures and, importantly, enable the identification of acetone and DMSO molecules in the powder samples.

Electron–phonon coupling and superconductivity in an alkaline earth hydride CaH6 at high pressures

Recently, an alkaline earth hydride CaH6 having a sodalitelike clathrate structure has been experimentally synthesized at megabar pressures with a maximum T c of 215 K, comparable to that of a rare earth hydride LaH10. Here, based on first-principles calculations, we find that CaH6 exhibits a huge peak in the Eliashberg spectral function α 2 F around the low-frequency region of H-derived phonon modes, in contrast to LaH10 having a widely spreading spectrum of α 2 F over the whole frequencies of H-derived phonon modes. It is revealed that the huge peak of α 2 F in CaH6 is associated with an effective electron–phonon coupling (EPC) between low-frequency optical phonons and hybridized H 1s and Ca 3d states near the Fermi energy. As pressure increases, the strengthened H–H covalent bonding not only induces a hardening of optical phonon modes but also reduces the electron–phonon matrix elements related to the low-frequency optical modes, thereby leading to a lowering of the EPC constant. It is thus demonstrated that H-derived low-frequency phonon modes play an important role in the pressure-induced variation of T c in CaH6. Furthermore, unlike the presence of two distinct superconducting gaps in LaH10, CaH6 is found to exhibit a single isotropic superconducting gap.

The phonon transport properties in a new ferroelectric carbon–boron framework with host–guest clathrate structure

The phonon transport properties in a new ferroelectric carbon–boron framework with host–guest clathrate structure

Quantum accumulation of electrical energy at interfacial boundaries in heterophase inorganic / organic clathrates

The work is devoted to the current problem of finding new ways and mechanisms of high-density electric energy accumulation. As a result of the conducted researches the system which allows to accumulate an electric charge at the expense of quantum effects and the phenomena without use of chemical reactions is offered. The basic idea was to form a material with a colossal area of the inner active surface with a sharply anisotropic chemical bonding character. Accordingly, the main goal was to create and study electrode materials based on intercalant heterophase structures with different types of hierarchy, capable of storing electrical energy at the quantum level. Based on the results of impedance spectroscopy, it was found that the obtained clathrate structures are promising for use as a cavitand electrode in a quantum battery, and, most importantly, can significantly increase its capacity

Multicomponent Quantum Mechanics/Molecular Mechanics Study of Hydrated Positronium.

We propose a model for solvated positronium (Ps) atoms in water, based on the sequential quantum mechanics/molecular mechanics (s-QM/MM) protocol. We developed a Lennard-Jones force field to account for Ps-water interactions in the MM step. The repulsive term was obtained from a previously reported model for the solvated electron, while the dispersion constant was derived from the Slater-Kirkwood formula. The force field was employed in classical Monte Carlo (MC) simulations to generate Ps-solvent configurations in the NpT ensemble, while the quantum properties were computed with the any-particle molecular orbital method in the subsequent QM step. Our approach is general, as it can be applied to other liquids and materials. One basically needs to describe the solvated electron in the environment of interest to obtain the Ps solvation model. The thermodynamical properties computed from the MC simulations point out similarities between the solvation of Ps and noble gas atoms, hydrophobic solutes that form clathrate structures. We performed convergence tests for the QM step, with particular attention to the choice of basis set and expansion centers for the positronic and electronic subsystems. Our largest model was composed of the Ps atom and 22 water molecules in the QM region, corresponding to the first solvation shell, surrounded by 128 molecules described as point charges. The mean electronic and positronic vertical detachment energies were (4.73 ± 0.04) eV and (5.33 ± 0.04) eV, respectively. The latter estimates were computed with Koopmans' theorem corrected by second-order self-energies, for a set of statistically uncorrelated MC configurations. While the Hartree-Fock wave functions do not properly account for the annihilation rates, they were useful for numerical tests, pointing out that annihilation is more sensitive to the choice of basis sets and expansion centers than the detachment energies. We further explored a model with reduced solute cavity size by changing the Ps-solvent force field. Although the pick-off annihilation lifetimes were affected by the cavity size, essentially the same conclusions were drawn from both models.

Clathrate structure of polymerized fullerite C60

Investigations of clathrate structures have gained a new impetus with the recent discovery of room-temperature superconductivity in metal hydrides. Here we report the finding, through density functional theory calculations, of a clathrate phase in the fullerite C60 system. Intermolecular bonds of the type 5/5 2+3 cycloaddition are induced between each C60 molecule and its twelve nearest neighbors in the face centered cubic lattice. Remarkably, this bonding creates on octahedral sites new C60 cages, identical to the original ones, and on tetrahedral sites distorted sodalite-like cages. The resulting carbon clathrate has a Pm3¯ simple cubic structure with half of the original face centered lattice constant. Eighty percent of its atoms are sp3-hybridized, driving a narrow-gap semiconducting behavior, a moderate bulk modulus of 268 GPa and an estimated hardness of 21.6 GPa. This new phase is likely to be prepared by subjecting C60 to high pressure and high temperature conditions.

Fermi surface topology and anisotropic superconducting gap in electron-doped hydride compounds at high pressure

The recent theoretical discovery of the predicted high-temperature superconductivity (superconducting transition temperature ${T}_{\mathrm{c}}\ensuremath{\sim}351\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ at 300 GPa) in clathrate ${\mathrm{Li}}_{2}\mathrm{Mg}{\mathrm{H}}_{16}$ is an important advance toward room-temperature superconductors. Here we use first-principle approaches to identify a new ternary hydride of clathrate structure of $Fd\overline{3}m\text{\ensuremath{-}}{\mathrm{Rb}}_{2}\mathrm{Mg}{\mathrm{H}}_{16}$ by Rb-doped $\mathrm{Mg}{\mathrm{H}}_{16}$ at 300 GPa. We first verified the thermal and dynamic stability for the $Fd\overline{3}m\text{\ensuremath{-}}{\mathrm{Rb}}_{2}\mathrm{Mg}{\mathrm{H}}_{16}$ through the formation enthalpy and phonon calculations, respectively. Next, we showcased that $Fd\overline{3}m\text{\ensuremath{-}}{\mathrm{Rb}}_{2}\mathrm{Mg}{\mathrm{H}}_{16}$ has two Fermi surface (FS) sheets, which are both dominated by the H2 $s$ orbital. Using the Eliashberg formalism, the ${T}_{\mathrm{c}}$ of $Fd\overline{3}m\text{\ensuremath{-}}{\mathrm{Rb}}_{2}\mathrm{Mg}{\mathrm{H}}_{16}$ was calculated to be 130 K at 300 GPa. Furthermore, the calculations of the electronic, phonon, and superconducting properties reveal that $Fd\overline{3}m\text{\ensuremath{-}}{\mathrm{Li}}_{2}\mathrm{Mg}{\mathrm{H}}_{16}$ has four FS sheets with mixed H1 $s$ and H2 $s$ orbital character and reaches the ${T}_{\mathrm{c}}$ of 352 K at 300 GPa. Compared with $Fd\overline{3}m\text{\ensuremath{-}}{\mathrm{Rb}}_{2}\mathrm{Mg}{\mathrm{H}}_{16}$, $Fd\overline{3}m\text{\ensuremath{-}}{\mathrm{Li}}_{2}\mathrm{Mg}{\mathrm{H}}_{16}$ produces high-frequency phonon softening, leading to the enhancement of ${T}_{\mathrm{c}}$. Moreover, it is demonstrated that Rb substitution for Li produces the reduction of contribution of H orbitals to the FS sheets and the decrease in FS sheets in number, which tend to decrease the electron-phonon coupling strength and ${T}_{\mathrm{c}}$. Our observed FS sheets and their associated superconducting gap will provide key insights into the understanding of the superconductivity mechanism in these and related systems.

Theory-directed discovery of high-temperature superconductivity in clathrate hydrides at high pressure

Theory-directed discovery of high-temperature superconductivity in clathrate hydrides at high pressure

Host-Guest Hydrogen Bonding in High-Pressure Acetone Clathrate Hydrates: In Situ Single-Crystal X-ray Diffraction Study.

The phenomenon of host-guest hydrogen bonding in clathrate hydrate crystal structures and its effect on physical and chemical properties have become subjects of extensive research. Hydrogen bonding has been studied for cubic (sI and sII) and hexagonal (sH) binary clathrates, while it has not been addressed for clathrate structures that exist at elevated pressures. Here, four acetone hydrate clathrates have been grown at high-pressure and low-temperature conditions. In situ single-crystal X-ray diffraction revealed that the synthesized phases possess already known trigonal (sTr), orthorhombic (sO), and tetragonal (sT) crystal structures as well as a previously unknown orthorhombic structure, so-called sO-II. Only sO and sII have previously been reported for acetone clathrates. Structural analysis suggests that acetone oxygens are hydrogen-bonded to the closest water oxygens of the host frameworks. Our discoveries show that clathrate hydrates hosting polar molecules are not as exotic as previously thought and could be stabilized at high-pressure conditions through hydrogen bonding.

The Systematic Study on the Stability and Superconductivity of Y‐Mg‐H Compounds under High Pressure

AbstractStructural stabilities of high‐pressure YMgHxphases (, and 16) and their superconductivities are investigated by employing evolutionary‐algorithm‐based crystal search combined with first‐principles calculations. For predicted candidate structures of YMgHx, the convex hull and phonon analyses reveal seven stable and two metastable phases. For all the predicted phases, superconducting transition temperatures (Tc) are also predicted by using the McMillan formula. ‐YMgH6is found having K at 300 GPa comparable to the boiling temperature of liquid nitrogen, and high‐Tc(≥77 K) being predicted for the H‐richer phases, ‐YMgH8(124 K at 300 GPa), ‐YMgH12(152 K at 250 GPa), and ‐YMgH12(190 K at 200 GPa), which possess clathrate structures composed of H14, H18, H24, and H24cages, respectively. To elucidate why the H‐rich phases attain high‐Tc, electronic and phonon band structures as well as electron–phonon coupling strength are analyzed based on Eliashberg spectral functions. The clathrate structures exhibit both a larger H‐driven electronic density of states at the Fermi level and a denser H‐driven phonon density of states, correlating with larger EPC constants. These structural and chemical bonding analyses reveal that the highest‐Tcphase ‐YMgH12has H4units formed in the sodalite cage.

Room-temperature superconductivity in boron- and nitrogen-doped lanthanum superhydride

Recent theoretical and experimental studies of hydrogen-rich materials at megabar pressures (i.e., >100 GPa) have led to the discovery of very high-temperature superconductivity in these materials. Lanthanum superhydride LaH$_{10}$ has been of particular focus as the first material to exhibit a superconducting critical temperature (T$_c$) near room temperature. Experiments indicate that the use of ammonia borane as the hydrogen source can increase the conductivity onset temperatures of lanthanum superhydride to as high as 290 K. Here we examine the doping effects of B and N atoms on the superconductivity of LaH$_{10}$ in its fcc (Fm-3m) clathrate structure at megabar pressures. Doping at H atomic positions strengthens the H$_{32}$ cages of the structure to give higher phonon frequencies that enhance the Debye frequency and thus the calculated T$_c$. The predicted T$_c$ can reach 288 K in LaH$_{9.985}$N$_{0.015}$ within the average high-symmetry structure at 240 GPa.

High-pressure synthesis of superconducting clathratelike YH4

Pursuing room-temperature superconductors has been a major theme in physics and material sciences since the discovery of superconductivity in 1911. In light of the tremendous progress that has been made in hydrogen-based superconductors with record ${T}_{c}\ensuremath{\sim}260\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ in binary fcc $\mathrm{La}{\mathrm{H}}_{10}$, it is natural to explore more similar phases in hydrogen-rich materials. Y and La are conventionally grouped together with the lanthanide elements due to the similarities in their outer electron configurations and properties. The yttrium-hydrogen system is the most attractive candidate with high ${T}_{c}$ among all binary metal-hydrogen systems theoretically studied so far. Here we report the synthesis of the $I4/mmm\text{\ensuremath{-}}\mathrm{Y}{\mathrm{H}}_{4}$ phase and determine its superconducting transition with maximum ${T}_{c}\ensuremath{\sim}88\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ at 155 GPa. The decrease in critical temperature under an external magnetic field suggests the upper critical magnetic field of about 14--22 T at megabar pressures consistent with theoretical data. By making the overlapping analysis, we elucidate that the stabilization of clathrate structures through Y atoms and the high-frequency hydrogen sublattice vibrations contribute effectively to strong electron-phonon coupling and therefore high-temperature superconductivity in the $I4/mmm\text{\ensuremath{-}}\mathrm{Y}{\mathrm{H}}_{4}$ and $Im\overline{3}m\text{\ensuremath{-}}\mathrm{Y}{\mathrm{H}}_{6}$ phases.

Inside and Out of the Pore: Comparing Interactions and Molecular Dynamics of Influenza A M2 Viroporin Complexes in Standard Lipid Bilayers.

Ion channels located at viral envelopes (viroporins) have a critical function for the replication of infectious viruses and are important drug targets. Over the last decade, the number and duration of molecular dynamics (MD) simulations of the influenza A M2 ion channel owing to the increased computational efficiency. Here, we aimed to define the system setup and simulation conditions for the correct description of the protein-pore and the protein-lipid interactions for influenza A M2 in comparison with experimental data. We performed numerous MD simulations of the influenza A M2 protein in complex with adamantane blockers in standard lipid bilayers using OPLS2005 and CHARMM36 (C36) force fields. We explored the effect of varying the M2 construct (M2(22-46) and M2(22-62)), the lipid buffer size and type (stiffer DMPC or softer POPC with or without 20% cholesterol), the simulation time, the H37 protonation site (Nδ or Νε), the conformational state of the W41 channel gate, and M2's cholesterol binding sites (BSs). We report that the 200 ns MD with M2(22-62) (having Nε Η37) in the 20 Å lipid buffer with the C36 force field accurately describe: (a) the M2 pore structure and interactions inside the pore, that is, adamantane channel blocker location, water clathrate structure, and water or chloride anion blockage/passage from the M2 pore in the presence of a channel blocker and (b) interactions between M2 and the membrane environment as reflected by the calculation of the M2 bundle tilt, folding of amphipathic helices, and cholesterol BSs. Strikingly, we also observed that the C36 1 μs MD simulations using M2(22-62) embedded in a 20 Å POPC:cholesterol (5:1) scrambled membrane produced frequent interactions with cholesterol, which when combined with computational kinetic analysis, revealed the experimentally observed BSs of cholesterol and suggested three similarly long-interacting positions in the top leaflet that have previously not been observed experimentally. These findings promise to be useful for other viroporin systems.

Understanding the Li and Na Intercalation in Si Clathrate Frameworks

Tetrel (Si, Ge, Sn) clathrates are host-guest structures that display novel electrochemical reactions with Li and Na due to their unique cage structure. One area of interest for Tetrel clathrates is the possibility of topotactic Li/Na insertion into the clathrate framework due to the open cage structure. The type II clathrate Na24-x(Si,Ge)136 is unique because the structure can be obtained without guest atoms in the clathrate framework. Figure 1 shows a crystal model schematic of the two unique polyhedral cages that comprise the type II Si clathrate structure: the dodecahedra (Si20, grey) and the hexakaidecahedra (Si28, blue). The structure usually forms with Na guest atoms (yellow) in the center of these cages, but when heated (300 – 500 °C ) under vacuum, the Na atoms diffuse and evaporate out of the structure resulting in a guest free clathrate, Si136.1 Once Na is removed the structure, Li intercalation into the vacant cages becomes possible.2 During the lithiation of the guest-free type II Si clathrate (Na1Si136), there is plateau at 0.30 V vs Li/Li+ which corresponds to Li intercalation into the vacant cages of the clathrate structure.2,3 With synchrotron powder X-ray diffraction, we confirm that Li intercalation is occurring in a topotactic fashion into the framework and identify the Li positions in the two types of cages. In the Si20 cage, Li is found near the center of the cages with a slightly split position, while Li in the Si28 cage is found very off-center, coordinated off the hexagonal faces. Density functional theory (DFT) calculations corroborate the Li positions in both cages. Next, we demonstrate that by using a voltage cutoff of 0.26 V, reversible Li insertion is possible as evidenced by the reproducible voltage profile. Due to the very low volume expansion (0.23 %) and reasonable capacity and voltage (230 mAh/g at 0.30 V), the type II Si clathrate has possible applications as an anode for Li-ion rechargeable batteries.In contrast to the room temperature intercalation of Li, we find that electrochemical deintercalation of Na from the type II structure requires high temperatures (350-450 °C) and overpotentials to achieve. We demonstrate electrochemical desodiation using a novel high temperature approach using a Na beta-alumina solid electrolyte.4 By using DFT to calculate the migration barriers for Na and Li, we demonstrate that the large differences between Li and Na intercalation originates from the much higher migration barriers for Na (1.0 - 2.0 eV) in the type II structure when compared to Li (0.2 eV). Based on these results, design rules for intercalation into Tetrel frameworks will be discussed and other promising open Tetrel frameworks highlighted. Figure 1: Crystal model schematic of the two types of polyhedral in the type II Si clathrate structure: the dodecahedra (grey) and the hexakaidecahedra (blue). Si atoms are orange and Na atoms are yellow. References (1) Krishna, L.; Baranowski, L. L.; Martinez, A. D.; Koh, C. A.; Taylor, P. C.; Tamboli, A. C.; Toberer, E. S. Efficient Route to Phase Selective Synthesis of Type II Silicon Clathrates with Low Sodium Occupancy. CrystEngComm 2014, 16, 3940–3949.(2) Langer, T.; Dupke, S.; Trill, H.; Passerini, S.; Eckert, H.; Pöttgen, R.; Winter, M. Electrochemical Lithiation of Silicon Clathrate-II. J. Electrochem. Soc. 2012, 159, A1318–A1322.(3) Dopilka, A.; Weller, J. M.; Ovchinnikov, A.; Childs, A.; Bobev, S.; Peng, X.; Chan, C. K. Structural Origin of Reversible Li Insertion in Guest‐Free, Type II Silicon Clathrates. Adv. Energy Sustain. Res. 2021, 2000114.(4) Dopilka, A.; Childs, A.; Bobev, S.; Chan, C. K. Solid-State Electrochemical Synthesis of Silicon Clathrates Using a Sodium-Sulfur Battery Inspired Approach. J. Electrochem. Soc. 2021, 168, 020516. Figure 1

Structural and Electrochemical Properties of the Type VIII Ba8Ga16–δ Sn30+δ (δ ≈ 1)clathrate during Lithiation

Clathrates of the Tetrel (Tt = Si, Ge, Sn) elements are host-guest structures that can undergo Li alloying reactions with high capacities. However, little is known about how the cage structure affects the phase transformations that take place during lithiation. To further this understanding, the structural changes of the type VIII clathrate Ba8Ga16–δSn30+δ (δ ≈ 1) during lithiation are investigated and compared to those in β-Sn with ex situ X-ray total scattering measurements and pair distribution function (PDF) analysis.The results show that the type VIII clathrate undergoes an alloying reaction to form Li-rich amorphous phases (Li x Ba0.17Ga0.33Sn0.67, x = 2 – 3) with local structures similar to those in the crystalline binary Li-Sn phases that form during the lithiation of β-Sn. As a result of the amorphous phase transition, the type VIII clathrate reacts at a lower voltage (0.25 V vs. Li/Li+) compared to β-Sn (0.45 V) and goes through a solid-solution reaction after the initial conversion of the crystalline clathrate phase. Cycling experiments suggest that the amorphous phase persists after the first lithiation and results in considerably better cycling than β-Sn. Density functional theory (DFT) calculations suggest that topotactic Li insertion into the clathrate lattice is not favorable due to the high energy of the Li sites, which is consistent with the experimentally observed amorphous phase transformation. The clathrate structure is hypothesized to kinetically circumvent the formation of Li-Sn or Li-Ga crystalline phases, which results in better cycling and a lower reaction voltage.The electrochemical lithiation pathway of Ba8Ga16–δSn30+δ (δ ≈ 1) is similar to that of the previously investigated type I Ba8Ge43 1 suggesting that the amorphous lithiation could be a common mechanism for guest-filled Tetrel clathrates. As amorphous phase transformations are a beneficial property for alloying anodes, Tetrel clathrates could act as precursors for obtaining amorphous phases with tunable electrochemical properties. With this assumption of a common mechanism for guest-filled clathrates, we will then discuss design rules for clathrate based alloying anodes in terms of optimizing the gravimetric capacity and reaction voltage. References (1) Dopilka, A.; Childs, A.; Bobev, S.; Chan, C. K. Understanding the Amorphous Lithiation Pathway of the Type I Ba8Ge43 Clathrate with Synchrotron X-Ray Characterization. Chem. Mater. 2020, 32, 9444–9457.

Possible high-T C superconductivity at 50 GPa in sodium hydride with clathrate structure

Ambient-pressure room-temperature superconductivity is one ultimate goal of science, for it will bring worldwide revolutionary changes in all kinds of technology. Several room temperature and near room temperature hydride superconductors at ultra high pressure (≳100 GPa) have been predicted theoretically. In particular, the hydrogen sulfide (H3S) with T C ≃ 203 K at 200 GPa has soon been confirmed experimentally, establishing a milestone toward room temperature superconductivity. However, high-T C superconductors at lower pressure (≲100 GPa) have not been reported before. In this work, we present high-T C superconductivity of 180 K at a relatively low pressure of 50 GPa in sodium hydride clathrate structure NaH6. The T C can be raised up to 206 K at 100 GPa, similar to the T C of H3S but at a much lower pressure. At 200 GPa, it reaches the highest T C of 210 K, slightly higher than that of H3S. The strong electron–phonon coupling strength given by the T 2g phonon mode at Γ point plays the key role in superconductivity. Our work demonstrates theoretically that hydrides could stabilize at a relatively low pressure and host high-T C superconductivity.

High-temperature superconductor of sodalite-like clathrate hafnium hexahydride

Hafnium hydrogen compounds have recently become the vibrant materials for structural prediction at high pressure, from their high potential candidate for high-temperature superconductors. In this work, we predict hbox {HfH}_{6} by exploiting the evolutionary searching. A high-pressure phase adopts a sodalite-like clathrate structure, showing the body-centered cubic structure with a space group of Imbar{3}m. The first-principles calculations have been used, including the zero-point energy, to investigate the probable structures up to 600 GPa, and find that the Imbar{3}m structure is thermodynamically and dynamically stable. This remarkable result of the Imbar{3}m structure shows the van Hove singularity at the Fermi level by determining the density of states. We calculate a superconducting transition temperature (T_{c}) using Allen-Dynes equation and demonstrated that it exhibits superconductivity under high pressure with relatively high-T_{c} of 132 K.