Stability Of Clathrate Research Articles

Exploring superconductivity in dynamically stable carbon-boron clathrates trapping molecular hydrogen

Exploring superconductivity in dynamically stable carbon-boron clathrates trapping molecular hydrogen

Predicted hot superconductivity in LaSc2H24 under pressure

The recent theory-driven discovery of a class of clathrate hydrides (e.g., CaH6, YH6, YH9, and LaH10) with superconducting critical temperatures (Tc) well above 200 K has opened the prospects for "hot" superconductivity above room temperature under pressure. Recent efforts focus on the search for superconductors among ternary hydrides that accommodate more diverse material types and configurations compared to binary hydrides. Through extensive computational searches, we report the prediction of a unique class of thermodynamically stable clathrate hydrides structures consisting of two previously unreported H24 and H30 hydrogen clathrate cages at megabar pressures. Among these phases, LaSc2H24 shows potential hot superconductivity at the thermodynamically stable pressure range of 167 to 300 GPa, with calculated Tcs up to 331 K at 250 GPa and 316 K at 167 GPa when the important effects of anharmonicity are included. The very high critical temperatures are attributed to an unusually large hydrogen-derived density of states at the Fermi level arising from the newly reported peculiar H30 as well as H24 cages in the structure. Our predicted introduction of Sc in the La-H system is expected to facilitate future design and realization of hot superconductors in ternary clathrate superhydrides.

Computational Screening and Stabilization of Boron-Substituted Type-I and Type-II Carbon Clathrates.

Boron substitution represents a promising approach to stabilize carbon clathrate structures, but no thermodynamically stable substitution schemes have been identified for frameworks other than the type-VII (sodalite) structure type. To investigate the possibility for additional tetrahedral carbon-based clathrate networks, more than 5000 unique boron decoration schemes were investigated computationally for type-I and type-II carbon clathrates with a range of guest elements including Li, Na, K, Rb, Cs, Mg, Ca, Sr, and Ba. Density functional theory calculations were performed at 10 and 50 GPa, and the stability and impact of boron substitution were evaluated. The results indicate that the boron-substituted carbon clathrates are stabilized under high-pressure conditions. Full cage occupancies of intermediate-sized guest atoms (e.g., Na, Ca, and Sr) are the most favorable energetically. Clathrate stability is maximized when the boron atoms are substituted within the hexagonal rings of the large [51262]/[51264] cages. Several structures with favorable formation enthalpies <-200 meV/atom were predicted, and type-I Ca8B16C30 is on the convex hull at 50 GPa. This structure represents the first thermodynamically stable type-I clathrate identified and suggests that boron-substituted carbon clathrates may represent a large family of diamond-like framework materials with a range of structure types and guest/framework substitutions.

Superhard lithium carbaboride clathrates

Lightweight strong boron-carbon clathrates adopting sodalite structure have been inspirated by the successful synthesis of the SrB3C3 compounds, which assuming the cubic bipartite sodalite structure. In this work, we designed series of stoichiometric LiBxC12-x and Li2BxC12-x (x = 1–6) compounds based on boron substitution of carbon in carbon sodalite structure using first-principles calculations. We found that LiB2C10, LiB3C9, LiB4C8, Li2B3C9 and Li2B4C8 are dynamically stable at high pressure and can be recovered under normal pressure. Strikingly, compared with inserting one Li atom into the B-C framework, inserting two Li atoms exhibit lower enthalpy value and better symmetry. Li2B4C8 is identified as the most stable structure among these compounds, and Li2B4C8 could potentially be synthesized at moderate pressure. The electron localization function calculations reveal that there is a strong covalent bond between B and C atoms in the clathrates, which forming the rigid three - dimensional crystalline networks. Moreover, the estimated Vickers hardness values of these five stable clathrates are 42 ∼ 51 GPa, which can be classified as superhard materials. At the same time, the pure shear strength of LiB2C10 is found to be 48.1 GPa, which exceeds the threshold value of 40 GPa. The pure shear strength of LiB3C9 (38.0 GPa) and Li2B3C9 (38.8 GPa) are found to be close to 40 GPa. Our work presents a new strategy for exploring superhard sodalite-like clathrate candidates.

Molecular Dynamics Simulations of the Stability and Dissociation of Structure-H Clathrate Hydrates in the Presence of Different Amino Acids, Gas Species, and sH Hydrate Formers

Molecular Dynamics Simulations of the Stability and Dissociation of Structure-H Clathrate Hydrates in the Presence of Different Amino Acids, Gas Species, and sH Hydrate Formers

Existence of Acetaldehyde Clathrate Hydrate and Its Dissociation Leading to Cubic Ice under Ultrahigh Vacuum and Cryogenic Conditions.

Acetaldehyde in a dilute aqueous solution gets hydrated to produce a geminal diol under atmospheric conditions. The acetaldehyde-water ice system under high pressure also converts to a geminal diol, and therefore, its stable clathrate hydrate (CH) phase, which in most systems forms at high pressures, is unknown. In the present study, we showed that acetaldehyde CH exists in ultrahigh vacuum (10-10 mbar) under cryogenic conditions (below 140 K) and continues to exist at 115 K for periods well over 1 day. Decomposition of acetaldehyde CH at 130-135 K produces water ice in its cubic crystalline form. The mechanism and kinetics involved in the process have also been studied. Reflection absorption infrared spectroscopy and temperature-programmed desorption mass spectrometry were utilized to confirm the CH formation. Our study establishes the possibility of a stable CH phase for acetaldehyde in interstellar and cometary environments.

Study on the clathrates and polymorphes of plant polyphenols

Gossypol is secondary metabolite that play diverse role in plant adaptation to environment. Obtained from cottonseeds gossypol has valuable biological properties and forms an abundant number of clathrates with a large variety of compounds. One of the primary reasons why gossypol can form clathrates is its ability to organize extensive hydrogen bonding networks due to its hydroxyl and aldehyde functional groups. Less hundred clathrates as single crystals have been obtained and their crystallographic parameters have been determined. Solutions were prepared by adding 0.5 g of gossypol and 6.0 ml (6.3 g) of acetic acid, 4.0 ml (3 g) of acetone, 5.0 ml (4.5 g) of ethyl acetate, 2 ml (2.0 g) of 1,4-dioxane, 9.0 ml (13.4 g) of chloroform, 11.0 ml (9.6 g) of benzene to six small glasses vials at room temperature. The structures of 30 inclusion complexes have been solved by diffraction methods. This natural polyphenol forms stable clathrates with acetic acid, acetone, ethyl acetate, 1,4-dioxane, chloroform and benzene. This work describes investigation of gossypol clathrates by single-crystal diffraction and thermal analysis.

Clathrate‐Like Alkali and Alkaline‐Earth Metal Borides: A New Family of Superconductors with Superior Hardness

AbstractConventional hard and superhard materials, such as diamond and cubic boron nitride, are attractive for fundamental material science and practical industrial application, but severely limited by their poor electrical conductivity. Therefore, it is desirable to design and fabricate novel materials for superior hardness and conductivity. Herein, a class of hard superconductors in alkali or alkaline‐earth metal (AM) borides, namely AMB7, constituted by a B23 cage with one centered metal atom (Li, Na, K, Mg, Ca, and Sr) is reported, which is the first stable clathrate structure in AMB systems. The theoretical calculations demonstrate that all these pressure‐stabilized clathrate structures can be quenched down to ambient conditions, which provides an essential prerequisite for experimental synthesis at moderate pressures. Among them, the highest hardness and maximum superconducting transition temperature (Tc) value are achieved in SrB7 (25.1 GPa) and MgB7 (29.3 K), respectively. Interestingly, the results show that KB7 simultaneously behaves high hardness (22.5 GPa) and superconducting transition temperature (Tc ≈26.2 K). This study opens up a new way to search and design novel superconductors with favorable mechanical properties under high pressure and high‐temperature conditions.

Mechanical stability of fluorinated-methane clathrate hydrates

• Lattice constant of clathrate hydrates formed by encapsulating fluorinated methane derivatives is greatly dictated by the number of fluorine atoms. • Polar fluorinated methane derivatives@cage show distinct rotational dynamics that vary with global strain. • Mechanical properties of clathrate hydrates are greatly influenced by the size and dipole moment of guests. • Unconventional water cages form as clathrate hydrates are mechanically failed via fractures of water cages. Clathrate hydrates recently find important practical applications in the capture and recovery of greenhouse gases, cold storage and refrigeration systems. Nevertheless, their properties at microscopic scale remains largely insufficient yet. Herein, the structure and stability of clathrate hydrates encapsulating fluorinated methane derivatives under mechanical load are investigated by molecular dynamics simulations. All investigated clathrate hydrates are structurally stable host-guest molecular crystals yet show distinct structural and mechanical behaviors. Lattice constant of those clathrate hydrates is dictated by the size and dipole moment of fluorinated methane, for example, it is initially enlarged with increasing fluorine atom in the methane guest molecule but followed by reduction as the guest molecule becomes tetrafluoromethane. However, clathrate hydrates encapsulating non-polar fluorinated methane show superior mechanical properties over those encapsulating polar ones. Polar fluorinated methane derivatives@clathrate cages exhibit distinct rotational dynamics that are influenced by strain. Moreover, all studied clathrate hydrates are mechanically failed by fractures of water cage accompanied by formation of unconventional clathrate cages. Those findings give insights into understanding the structural, thermodynamic stability and mechanical properties of clathrate hydrates encapsulating fluorinated guests.

High-temperature superconducting ternary Li−R−H superhydrides at high pressures (R=Sc,Y,La)

Compressed clathrate superhydrides have been the most promising candidates for room-temperature superconductors since the theory-oriented findings of ${\mathrm{CaH}}_{6}, {\mathrm{YH}}_{9}, {\mathrm{LaH}}_{10}$ et. al., where the hydrogen clathrate framework was believed to play a critical role in improving superconductivity. Recently, a ternary superhydride of ${\mathrm{Li}}_{2}{\mathrm{MgH}}_{16}$ was predicted to be a ``hot'' superconductor with a theoretical ${T}_{c}$ value up to 473 K at 250 GPa, although it exhibits the metastable feature under high pressure. With the aim of seeking thermodynamically stable ternary clathrate superhydrides, by exploring the high-pressure phase diagram of the $\mathrm{Li}\text{--}R\text{--}\mathrm{H} (R=\mathrm{Sc},\mathrm{Y},\phantom{\rule{0.28em}{0ex}}\text{and}\phantom{\rule{0.28em}{0ex}}\mathrm{La})$ systems at 300 GPa, we identified several thermodynamically ternary superhydrides with high-temperature superconductivity. Among these predicted stable structures, as a result of extensive simulations, clathrate structured ${\mathrm{Li}}_{2}{\mathrm{YH}}_{17}$ and ${\mathrm{Li}}_{2}{\mathrm{LaH}}_{17}$ are predicted to be high-temperature superconductors with a superconducting critical temperature (${T}_{c}$) up to 108 and 156 K, at 200 and 160 GPa, respectively. Interestingly, a superhydride, $Immm$--${\mathrm{Li}}_{2}{\mathrm{ScH}}_{20}$, with mixed molecular and atomic hydrogen, is predicted to possess a high ${T}_{c}$ of 242 K at 300 GPa. The present results may stimulate the future experiment for the investigation of structural, electronic, and superconducting properties of metal-doped rare-earth superhydrides, which thus help the further design and discovery of superconducting clathrate superhydrides.

Pressure-induced evolution of crystal and electronic structure of neptunium hydrides.

An extensive exploration of high-pressure phase diagrams of NpHx (x = 1-10) compounds was performed by using swarm-intelligence-based CALYPSO structure searches. We propose five stable hydrogen-rich clathrate phases (P4/nmm-NpH5, Cmcm-NpH7, Fm3̄m-NpH8, P63/mmc-NpH9, and Fm3̄m-NpH10) that are composed of unusual H cages with stoichiometries H20, H24, H29, and H32 in which the H atoms are weakly covalently bonded to one another, with neptunium atoms occupying centers of the cages. The electronic structure analyses show that these predicted hydrogen-rich structures are all metallic phases, and Np-H and H-H bonds are formed by ionic and covalent bond interactions, respectively. The charge transfer from the Np atom plays an important role in the stability of the proposed structures. All hydrogen-rich clathrate structures show superconductivity behavior in their respective stability pressure range. Our work is an important step in understanding the phase stability and bonding behavior of NpHx under extreme conditions and provides a valuable reference for experimental synthesis and identification of cage-like neptunium hydrides.

Strengthening and weakening of methane hydrate by water vacancies

Gas clathrate hydrates show promising applications in sustainable technologies such as future energy resources, gas capture and storage. The stability of clathrate hydrates under external load is of great crucial to those important applications, but remains unknown. Water vacancy is a common structural defect in clathrate hydrates. Herein, the mechanical characteristics of sI methane hydrates containing three types of water vacancy are investigated by molecular dynamics simulations with four different water forcefields. Mechanical properties of methane hydrates such as tensile strength are dictated not only by the density but also the type of water vacancy. Surprisingly, the tensile strength of methane hydrates can be weakened or strengthened, depending on the adopted water model and water vacancy density. Strength enhancement mainly results from the formation of new water cages. This work provides critical insights into the mechanics and microstructural properties of methane clathrate hydrates under external load, which is of primary importance in the recovery of natural gas from methane hydrate reservoirs. Cited as: Lin, Y., Liu, Y., Xu, K., Li, T., Zhang, Z., Wu, J. Strengthening and weakening of methane hydrate by water vacancies. Advances in Geo-Energy Research, 2022, 6(1): 23-37. https://doi.org/10.46690/ager.2022.01.03

Structural and mechanical stability of clathrate hydrates encapsulating monoatomic guest species

Clathrate hydrate (CH) structures find diversely promising applications such as gas and energy storage and transport, carbon capture and storage, gas separation, water desalination, and food and pharmaceutical engineering. However, the influence of guest molecules on their properties remains largely uncharacterized. Here, the critical roles of monoatomic guest size and interaction strength with water molecule in the structural and mechanical stability of clathrate hydrates are explicitly examined by classical molecular dynamics simulations. With increasing guest size or its interaction strength, the lattice constant and mechanical properties such as Young’s modulus, tensile strength, Poisson’s ratio of CHs vary nonlinearly. Based on the characteristics of the contour map of lattice constant, four regions of lattice constant of CHs can be divided. Interestingly, there are crossovers in the iso-lattice constant lines and tensile strength. Upon uniaxial tension, CH destabilizes via brittle or ductile failure, relying on the size and interaction strength of monoatomic guest. The guest size and interaction strength dependent properties can be critically understood by radial distribution function, cage volume and distribution of guest@cages.

A synthesis and crystal structures of three inclusion compounds of Bis(4-hydroxyphenyl) Sulfone and tetraalkylammonium

In this paper, three inclusion compounds formed by Bis(4-hydroxyphenyl) Sulfone and tetramethylammonium cation, tetrapropylammonium cation and tetrabutylammonium cation were prepared: 4(CH3)4N+·2C12H9O4S-·C12H8O4S2-·3C12H10O4S·7H2O (1), (n-C3H7)4N+·C12H9O4S-·0.5H2O (2), 2(n-C4H9)4N+ ·2 C12H9O4S- ·C12H10O4S (3), then the complexes were characterized by X-ray single crystal diffraction. The results show that 1 and three belong to the monoclinic P21/c space group, while two belongs to the monoclinic Cc space group. Among the three clathrate crystal structures, one shows the anion hydrogen bond network structure with "Hourglass"-shaped pores constructed by the host molecule and its anion and water molecule; two rectangular holes are constructed from the host anion and water molecules, and these holes are repeatedly arranged to obtain a 3 D host hydrogen bond network structure; the host molecules and their anions in 3 form discrete "molecular pillars" and further pile up to form the main frame structure. As for the tetraalkylammonium cation as the guest template, they are respectively filled in the above-mentioned host frame structure to form the final stable clathrate crystal structure.

Stability and bonding nature of clathrate H cages in a near-room-temperature superconductor LaH10

Lanthanum hydride (${\mathrm{LaH}}_{10}$) with a sodalitelike clathrate structure was experimentally synthesized to exhibit a near-room-temperature superconductivity under megabar pressures. Based on first-principles density-functional theory calculations, we reveal that the metal framework of La atoms has excess electrons at interstitial regions. Such anionic electrons are easily captured to form a stable clathrate structure of H cages. We thus propose that the charge transfer from La to H atoms is mostly driven by the electride property of the La framework. Furthermore, the interaction between La atom and H cage induces a delocalization of La $5p$ semicore states to hybridize with the H $1s$ state. Consequently, the bonding nature of ${\mathrm{LaH}}_{10}$ is characterized as a mixture of ionic and covalent bonding between La atom and H cage. Our findings demonstrate that anionic and semicore electrons play important roles in stabilizing clathrate H cages in ${\mathrm{LaH}}_{10}$, which can be broadly applicable to other compressed rare-earth hydrides with clathrate structures.

Hydrogen Clathrate Structures in Uranium Hydrides at High Pressures.

Room-temperature superconductivity has always been an area of intensive research. Recent findings of clathrate metal hydrides structures have opened up the doors for achieving room-temperature superconductivity in these materials. Here, we report first-principles calculations for stable H-rich clathrate structures of uranium hydrides at high pressures. The clathrate uranium hydrides contain H cages with stoichiometries of H24, H29, and H32, in which H atoms are bonded covalently to other H atoms, and U atoms occupy the centers of the cages. Especially, a UH10 clathrate structure containing H32 cages is predicted to have an estimated Tc higher than 77 K at high pressures.

Tensile properties of structural I clathrate hydrates: Role of guest—host hydrogen bonding ability

Clathrate hydrates (CHs) are one of the most promising molecular structures in applications of gas capture and storage, and gas separations. Fundamental knowledge of mechanical characteristics of CHs is of crucial importance for assessing gas storage and separations at cold conditions, as well as understanding their stability and formation mechanisms. Here, the tensile mechanical properties of structural I CHs encapsulating a variety of guest species (CH4, NH3, H2S, CH2O, CH3OH, and CH3SH) that have different abilities to form hydrogen (H-) bonds with water molecule are explored by classical molecular dynamics (MD) simulations. All investigated CHs are structurally stable clathrate structures. Basic mechanical properties of CHs including tensile limit and Young’s modulus are dominated by the H-bonding ability of host-guest molecules and the guest molecular polarity. CHs containing small CH4, CH2O and H2S guest molecules that possess weak H-bonding ability are mechanically robust clathrate structures and mechanically destabilized via brittle failure on the (101) plane. However, those entrapping CH3SH, CH3OH, and NH3 that have strong H-bonding ability are mechanically weak molecular structures and mechanically destabilized through ductile failure as a result of gradual global dissociation of clathrate cages.

On the Occurrence of Clathrate Hydrates in Extreme Conditions: Dissociation Pressures and Occupancies at Cryogenic Temperatures with Application to Planetary Systems

Abstract We investigate the thermodynamic stability of clathrate hydrates at cryogenic temperatures from the 0 K limit to 200 K in a wide range of pressures, covering the thermodynamic conditions of interstellar space and the surface of the hydrosphere in satellites. Our evaluation of the phase behaviors is performed by setting up quantum partition functions with variable pressures on the basis of a rigorous statistical mechanics theory that requires only the intermolecular interactions as input. Noble gases, hydrocarbons, nitrogen, and oxygen are chosen as the guest species, which are key components of the volatiles in such satellites. We explore the hydrate/water two-phase boundary of those clathrate hydrates in water-rich conditions and the hydrate/guest two-phase boundary in guest-rich conditions, either of which occurs on the surface or subsurface of icy satellites. The obtained phase diagrams indicate that clathrate hydrates can be in equilibrium with either water or the guest species over a wide range far distant from the three-phase coexistence condition and that the stable pressure zone of each clathrate hydrate expands significantly on intense cooling. The implication of our findings for the stable form of water in Titan is that water on the surface exists only as clathrate hydrate with the atmosphere down to a shallow region of the crust, but clathrate hydrate in the remaining part of the crust can coexist with water ice. This is in sharp contrast to the surfaces of Europa and Ganymede, where the thin oxygen air coexists exclusively with pure ice.

Stability and composition of CH4-rich clathrate hydrates in the present martian subsurface

In the past years, multiple detections of methane in Mars' atmosphere have raised numerous questions about its potential sources. Independently of methane formation mechanism(s), CH4 produced in the past or at the present day could be stored in subsurface reservoirs such as clathrate hydrates. In this work, global maps of stability depth of CH4-rich clathrate hydrates in the martian soil are obtained by including in the subsurface model a top layer with thermal properties that fit with the thermal inertia derived from MGS TES observations (Putzig and Mellon, 2007) and by taking into account the spatial variations of the surface heat flow (Parro et al., 2017). In addition, the spatial distribution of stable methane clathrates is investigated in the presence of eutectic NaCl and CaCl2 brines. The influence of gas phase composition on clathrate stability and on guests abundance is also examined by considering the CO2-CH4-N2 and CO2CH4-H2 mixtures.On present-day Mars, the stability conditions of CH4-rich clathrates are met at a depth of a few meters in high latitude regions and at a few tens of meters deep at the equator. The top of their stability zone is the deepest (~68 m) in regions where methane has been locally reported, especially in the area observed by Mumma et al. (2009). It is also in that particular region that the methane clathrate stability zone is the least extended in the martian subsurface, its base reaching ~8 km deep in the presence of pure water. This depth can even be 4 times shallower if methane clathrates form in the presence of eutectic CaCl2 brine. Moreover, the incorporation of nitrogen and hydrogen in mixed CO2-CH4 clathrates allows a better trapping of methane but their presence increases the formation pressure and therefore their stability depth.

Proton-transfer in 1,1,3,3 tetramethyl guanidine by means of ultrasonic relaxation and Raman spectroscopies and molecular orbital calculations.

In this work, we report on the structure and dynamics of the 1,1,3,3 tetramethyl guanidine (TMG) aqueous solutions in a wide concentration and temperature range by combining vibrational and ultrasonic spectroscopies. The experimental Raman spectra have been compared with the corresponding spectra obtained by ab initio quantum mechanical and density functional theory electronic structure calculations. This comparison indicated that only a single mechanism occurs when dissolving TMG in water and this is the proton transfer reaction, while the formation of byproducts during hydrolysis of TMG is dubious. This observation is further supported by the concentration dependence of the Raman spectra. The analysis of the ultrasonic relaxation data also revealed that the system exhibits a single relaxation process associated with this proton transfer reaction. It has been also observed that both relaxation amplitude and frequency exhibit a clear monotonous increase with increasing amine concentration in the solutions supporting the concept of the proton transfer reaction. The corresponding activation enthalpy was estimated directly from the temperature dependence of the acoustic data and found equal to ΔH*=5.56±0.34kcal/mol, which seems to be reasonable for hydrogen-bond formation. Furthermore, the concentration dependence of the acoustic parameters and kinematic viscosity data has been used as a probe for the molecular association in these solutions. The results have been discussed in relation to the ability or inability of water molecules to form stable clathrates after the addition of amine molecules in the solutions.