Existence of density inhomogeneity of liquid Te associated with liquid-liquid phase transition.

We performed small-angle X-ray scattering measurements of liquid Te using a synchrotron radiation facility and observed maximum scattering intensity near 620 K in the supercooled region (melting temperature 723 K). This indicates that density inhomogeneity exists in liquid Te, and the fact that this temperature coincides with the temperature at which the specific heat, sound velocity, and thermal expansion coefficient reach their maxima means that this density inhomogeneity is the cause of these thermodynamic anomalies. The thermodynamic anomalies in liquid Te had already been shown in the 1980s to be comprehensively explained by the inhomogeneity associated with the continuous liquid-liquid phase transition (LLT), but direct experimental evidence for the existence of the inhomogeneity had not been obtained. The present results, together with those already obtained for mixture systems (Te-Se, Te-Ge), indicate the existence of inhomogeneity associated with LLT in liquid Te systems, and strongly support the model. Recently, similarmaximum scattering intensity has also been observed in supercooled liquid water, which exhibits thermodynamic anomalies similar to those of Te, indicating the universality of the inhomogeneous model or LLT scenario to explain the thermodynamics of such "anomalous liquids". Further development of the LLT scenario is expected in near future. .

Supercritical Gallium Trichloride in Oxidative Metal Recycling: Ga2Cl6 Dimers vs GaCl3 Monomers and Rheological Behavior.

Oxidative recycling of metals is crucial for a circular economy, encompassing the preservation of natural resources, the reduction of energy consumption, and the mitigation of environmental impacts and greenhouse gas emissions associated with traditional mining and processing. Low-melting gallium trichloride appears to be a promising oxidative solvent for rare-earth metals, transuranium elements, platinum, pnictogens, and chalcogens. Typically, oxidative dissolution with GaCl3 occurs at relatively low temperatures over a few days, assuming the presence of tetrahedral Ga-Cl entities. While supercritical gallium trichloride holds the potential for advanced recycling, little is known about its structure and viscosity. Using high-energy X-ray diffraction and multiscale modeling, which includes first-principles simulations, we have revealed a dual molecular nature of supercritical gallium trichloride, consisting of tetrahedral dimers and flat trigonal monomers. The molecular geometry can be precisely tuned by adjusting the temperature and pressure, optimizing the recycling process for specific metals. The derived viscosity, consistent with the reported results in the vicinity of melting, decreases by a factor of 100 above the critical temperature, enabling fast molecular diffusion, and efficient recycling kinetics.

Magnetic Supramolecular Spherical Arrays: Direct Formation of Micellar Cubic Mesophase by Lanthanide Metallomesogens with 7-Coordination Geometry.

Here, an unprecedented phenomenon in which 7-coordinate lanthanide metallomesogens, which align via hydrogen bonds mediated by coordinated H2 O molecules, form micellar cubic mesophases at room temperature, creating body-centered cubic (BCC)-type supramolecular spherical arrays, is reported. The results of experiments and molecular dynamics simulations reveal that spherical assemblies of three complexes surrounded by an amorphous alkyl domain spontaneously align in an energetically stable orientation to form the BCC structure. This phenomenon differs greatly from the conventional self-assembling behavior of 6-coordinated metallomesogens, which form columnar assemblies due to strong intermolecular interactions. Since the magnetic and luminescent properties of different lanthanides vary, adding arbitrary functions to spherical arrays is possible by selecting suitable lanthanides to be used. The method developed in this study using 7-coordinate lanthanide metallomesogens as building blocks is expected to lead to the rational development of micellar cubic mesophases.

In situ high-pressure pair distribution function measurement of liquid and glass by using 100 keV pink beam.

Understanding the pressure-induced structural changes in liquids and amorphous materials is fundamental in a wide range of scientific fields. However, experimental investigation of the structure of liquid and amorphous material under in situ high-pressure conditions is still limited due to the experimental difficulties. In particular, the range of the momentum transfer (Q) in the structure factor [S(Q)] measurement under high-pressure conditions has been limited at relatively low Q, which makes it difficult to conduct detailed structural analysis of liquid and amorphous material. Here, we show the in situ high-pressure pair distribution function measurement of liquid and glass by using the 100 keV pink beam. Structures of liquids and glasses are measured under in situ high-pressure conditions in the Paris-Edinburgh press by high-energy x-ray diffraction measurement using a double-slit collimation setup with a point detector. The experiment enables us to measure S(Q) of GeO2 and SiO2 glasses and liquid Ge at a wide range of Q up to 20-29 Å-1 under in situ high-pressure and high-temperature conditions, which is almost two times larger than that of the conventional high-pressure angle-dispersive x-ray diffraction measurement. The high-pressure experimental S(Q) precisely determined at a wide range of Q opens the way to investigate detailed structural features of liquids and amorphous materials under in situ high-pressure and high-temperature conditions, as well as ambient pressure study.

Atomic and Electronic Structure in MgO-SiO2.

Understanding disordered structure is difficult due to insufficient information in experimental data. Here, we overcome this issue by using a combination of diffraction and simulation to investigate oxygen packing and network topology in glassy (g-) and liquid (l-) MgO-SiO2 based on a comparison with the crystalline topology. We find that packing of oxygen atoms in Mg2SiO4 is larger than that in MgSiO3, and that of the glasses is larger than that of the liquids. Moreover, topological analysis suggests that topological similarity between crystalline (c)- and g-(l-) Mg2SiO4 is the signature of low glass-forming ability (GFA), and high GFA g-(l-) MgSiO3 shows a unique glass topology, which is different from c-MgSiO3. We also find that the lowest unoccupied molecular orbital (LUMO) is a free electron-like state at a void site of magnesium atom arising from decreased oxygen coordination, which is far away from crystalline oxides in which LUMO is occupied by oxygen's 3s orbital state in g- and l-MgO-SiO2, suggesting that electronic structure does not play an important role to determine GFA. We finally concluded the GFA of MgO-SiO2 binary is dominated by the atomic structure in terms of network topology.

Pressure-induced reversal of Peierls-like distortions elicits the polyamorphic transition in GeTe and GeSe.

While polymorphism is prevalent in crystalline solids, polyamorphism draws increasing interest in various types of amorphous solids. Recent studies suggested that supercooling of liquid phase-change materials (PCMs) induces Peierls-like distortions in their local structures, underlying their liquid-liquid transitions before vitrification. However, the mechanism of how the vitrified phases undergo a possible polyamorphic transition remains elusive. Here, using high-energy synchrotron X-rays, we can access the precise pair distribution functions under high pressure and provide clear evidence that pressure can reverse the Peierls-like distortions, eliciting a polyamorphic transition in GeTe and GeSe. Combined with simulations based on machine-learned-neural-network potential, our structural analysis reveals a high-pressure state characterized by diminished Peierls-like distortion, greater coherence length, reduced compressibility, and a narrowing bandgap. Our finding underscores the crucial role of Peierls-like distortions in amorphous octahedral systems including PCMs. These distortions can be controlled through pressure and composition, offering potentials for designing properties in PCM-based devices.

Siliceous zeolite-derived topology of amorphous silica.

The topology of amorphous materials can be affected by mechanical forces during compression or milling, which can induce material densification. Here, we show that densified amorphous silica (SiO2) fabricated by cold compression of siliceous zeolite (SZ) is permanently densified, unlike densified glassy SiO2 (GS) fabricated by cold compression although the X-ray diffraction data and density of the former are identical to those of the latter. Moreover, the topology of the densified amorphous SiO2 fabricated from SZ retains that of crystalline SZ, whereas the densified GS relaxes to pristine GS after thermal annealing. These results indicate that it is possible to design new functional amorphous materials by tuning the topology of the initial zeolitic crystalline phases.

Revealing the evolution of local structures in the formation process of alkaline earth metal cation-containing zeolites from glasses.

Alkaline earth metal cations are ubiquitously present in natural zeolites but less exploited in synthetic zeolites due to their low solubility in water, and hence it remains elusive how they contribute to zeolite formation. Herein, harmotome, a PHI-type zeolite with Ba2+, is readily synthesized from a Ba-containing aluminosilicate glass. This glass-to-zeolite transformation process, in particular the structure-regulating role of Ba2+, is investigated by anomalous X-ray scattering and high-energy X-ray total scattering techniques. The results demonstrate that the steady Ba2+-aluminosilicate interactions not only help prevent the precipitation of barium species under alkaline synthetic conditions, but also dictate the local structures with distinct interatomic distances between the Ba2+ and the surrounding aluminosilicate species throughout the transformation process, which lead to the successful formation of harmotome without detectable impurities. This study highlights the usefulness of the comprehensive X-ray scattering techniques in revealing the formation scheme of the zeolites containing specific metal species. In addition, a promising alternative approach to design and synthesize zeolites with unique compositions and topologies by using well-crafted glasses with suitable metal cation dopants is demonstrated.

Atomic Three-Dimensional Investigations of Pd Nanocatalysts for Acetylene Semi-hydrogenation.

Deciphering the three-dimensional (3D) insight into nanocatalyst surfaces at the atomic level is crucial to understanding catalytic reaction mechanisms and developing high-performance catalysts. Nevertheless, better understanding the inherent insufficiency of a long-range ordered lattice in nanocatalysts is a big challenge. In this work, we report the local structure of Pd nanocatalysts, which is beneficial for demonstrating the shape-structure-adsorption relationship in acetylene hydrogenation. The 5.27 nm spherical Pd catalyst (Pdsph) shows an ethylene selectivity of 88% at complete acetylene conversion, which is much higher than those of the Pd octahedron and Pd cube and superior to other reported monometallic Pd nanocatalysts so far. By virtue of the local structure revelation combined with the atomic pair distribution function (PDF) and reverse Monte Carlo (RMC) simulation, the atomic surface distribution of the unique compressed strain of Pd-Pd pairs in Pdsph was revealed. Density functional theory calculations verified the obvious weakening of the ethylene adsorption energy on account of the surface strain of Pdsph. It is the main factor to avoid the over-hydrogenation of acetylene. The present work, entailing shape-induced surface strain manipulation and atomic 3D insight, opens a new path to understand and optimize chemical activity and selectivity in the heterogeneous catalysis process.

Creating glassy states of dicarboxylate-bridged coordination polymers.

We report the direct formation of dicarboxylate-based coordination polymer glasses through thermal dehydration. The rearrangement of the coordination networks caused by dehydration was monitored by in situ powder X-ray diffraction, infrared spectroscopy, and synchrotron X-ray characterizations. The microporosity and mechanical properties of these glasses were investigated.

Structural analysis and ionic conduction mechanism of sulfide-based solid electrolytes doped with Br.

Sulfide glasses can exhibit notable ionic conductivity because of annealing-associated crystallization. One well-known example is Li7P3S11. Our research showed that adding bromine (Br) to Li3PS4 sulfide glass results in a similar crystal structure and high ionic conductivity comparable to that of another compound Li10GeP2S12. This structure differs from the PS4 anion framework of Li3PS4. In addition, the ionic conductivity decreases owing to a structural transition to the ß-phase. Herein, we present our findings on the local structure of Li3PS4 sulfide glass and its crystallized glass ceramic with the addition of Br. This analysis relies on the pair distribution function analysis obtained from high-energy X-ray diffraction. Moreover, using the bond valence sum method, we verified that incorporating Br promotes the formation of Li ionic conduction pathways. Our results indicate that precise control over the anion molecular structure by introducing halogens holds promise for achieving high Li-ion conductivity.

Hydration of Alkali Metal and Halide Ions from Static and Dynamic Viewpoints.

Ion hydration in aqueous solutions plays a paramount role in many fields. Despite many studies on ion hydration, the nature of ion hydration is not consistently understood at the molecular level. Combining neutron scattering (NS), wide-angle X-ray scattering (WAXS), and molecular dynamics (MD), we quantify the ionic hydration degree (hydration ability) systematically for a series of alkali metal and halide ions based on static and dynamic hydration numbers. The former is based on the orientational correlation of water molecules bound to an ion derived from the positional information from NS and WAXS. The latter is defined as the mean number of water molecules remaining in the first coordination shell of an ion over a residence time of bound water molecules around the ion from MD. The static and dynamic hydration numbers distinguish hydration from coordination and quantify the ionic hydration degree, which provides a valuable reference for understanding various phenomena in nature.

Alkali Metal Ion Recognition by 18-Crown-6 in Aqueous Solutions: Evidence from Local Structures.

The underlying recognition mechanisms of alkali metal ions by crown ethers in aqueous solutions are yet to be fully understood at the molecular level. We report direct experimental and theoretical evidence for the structure and recognition sequence of alkali metal ions (Li+, Na+, K+, Rb+, and Cs+) by 18-crown-6 in aqueous solutions by wide-angle X-ray scattering combined with an empirical potential structure refinement modeling and ab initio molecular dynamics simulation. Li+, Na+, and K+ are located in the negative potential cavity of 18-crown-6, with Li+ and Na+ deviating from the centroid of 18-crown-6 by 0.95 and 0.35 Å, respectively. Rb+ and Cs+ lie outside the 18-crown-6 ring and deviate from the centroid of 18-crown-6 by 0.05 and 1.35 Å, respectively. The formation of the 18-crown-6/alkali metal ion complexes is dominated by electrostatic attraction between the cations and the oxygen atoms (Oc) of 18-crown-6. Li+, Na+, K+, and Rb+ form the H2O···18-crown-6/cation···H2O "sandwich" hydrates, while water molecules only hydrate with Cs+ of the 18-crown-6/Cs+ complex on the same side of Cs+. Based on the local structure, the recognition sequence of 18-crown-6 for alkali metal ions in an aqueous solution follows K+ > Rb+ >Na+ >Li+, which is completely different from that (Li+ > Na+ > K+ > Rb+ > Cs+) in the gas phase, confirming that the solvation medium seriously affects the cation recognition of crown ethers. This work provides atomic insights into understanding the host-guest recognition and solvation behavior of crown ether/cation complexes.

Atom-Selective Analyses Reveal the Structure-Directing Effect of Cs Cation on the Synthesis of Zeolites.

To understand the crystallization mechanism of zeolites, it is important to clarify the detailed role of the structure-directing agent, which is essential for the crystallization of zeolite, interacting with an amorphous aluminosilicate matrix. In this study, to reveal the structure-directing effect, the evolution of the aluminosilicate precursor which causes the nucleation of zeolite is analyzed by the comprehensive approach including atom-selective methods. The results of total and atom-selective pair distribution function analyses and X-ray absorption spectroscopy indicate that a crystalline-like coordination environment gradually forms around Cs cations. This corresponds to the fact that Cs is located at the center of the d8r units in the RHO structure whose unit is unique in this zeolite, and a similar tendency is also confirmed in the ANA system. The results collectively support the conventional hypothesis that the formation of the crystalline-like structure before the apparent nucleation of the zeolite.

In situ Raman and X-ray scattering of a single supersaturated aqueous Mg(NO3)2 droplet ultrasonically levitated.

A single liquid droplet in the air generated by ultrasonic levitation provides such analytical advantages as a small sample volume (~ µL) for expensive proteins, container-free condition for deeply supercooling and supersaturation, time-dependent observation, and homogeneous rapid mixing. The investigation of the properties and structure of a droplet at a molecular level is highly needed for understanding the physicochemical behaviors of a droplet and an underlying mechanism of processes in the droplet. We develop in situ Raman and synchrotron X-ray scattering methods of a single liquid droplet of ~ 1 mm size ultrasonically levitated. The composition of a supersaturated Mg(NO3)2 droplet and speciation in the droplet are determined by analyzing the nitrate N-O and the water O-H stretching vibrational Raman bands. The X-ray interference function of an supersaturated Mg(NO3)2 droplet is subjected to an empirical potential structure refinement modeling to reveal the ion solvation, association, and solvent water structure. Furthermore, crystallization of Mg(NO3)2⋅nH2O from a saturated droplet is observed and identified.

Structure of choline chloride-carboxylic acid deep eutectic solvents by wide-angle X-ray scattering and DFT calculations.

Choline chloride (ChCl)-carboxylic acid deep eutectic solvents (DESs) are promising green solvents for lignocellulose pretreatment, de-aromatization of gasoline, battery recycling, etc. Micro interactions determine the physical properties of DESs, such as melting point, viscosity, and solubility. In the present work, the structures of choline chloride/formic acid (FA) and choline chloride/acetic acid (AA) with a 1 : 2 molar ratio were investigated by wide-angle X-ray scattering, empirical potential structure refinement (EPSR) and density functional theory (DFT) calculations. Reduced density gradient (RDG) and atoms in molecules (AIM) show that hydrogen bonds and carbon-hydrogen bonds exist in choline chloride-carboxylic acid DESs. EPSR modelling based on the gauche choline cation model reveals the interactions between DES components. Cl- plays an important role in maintaining the structural stability of choline chloride-carboxylic acid DESs, by participating in the formation of hydrogen bonds, carbon-hydrogen bonds, and acting as a bridge for indirect interaction, including between choline cations and carboxylic acid molecules. Molecular size and steric hindrance elucidate the formation of different sizes of clusters (≤10 molecules) and chains (≤5 molecules) in DESs. Spatial density functions show that formic acid and acetic acid have a strong orientational preference. The strong interaction between Ch+ and FA and the existence of the Cl- bridge significantly destroyed the lattice structure of ChCl, resulting in the melting point of ChClFA (<-90 °C) being lower than that of ChClAA (-8.98 °C). This fundamental understanding of the structure will enable the development of green, economical, and nontoxic choline chloride-carboxylic acid DESs.

A near dimensionally invariable high-capacity positive electrode material.

Delivering inherently stable lithium-ion batteries is a key challenge. Electrochemical lithium insertion and extraction often severely alters the electrode crystal chemistry, and this contributes to degradation with electrochemical cycling. Moreover, electrodes do not act in isolation, and this can be difficult to manage, especially in all-solid-state batteries. Therefore, discovering materials that can reversibly insert and extract large quantities of the charge carrier (Li+), that is, high capacity, with inherent stability during electrochemical cycles is necessary. Here lithium-excess vanadium oxides with a disordered rocksalt structure are examined as high-capacity and long-life positive electrode materials. Nanosized Li8/7Ti2/7V4/7O2 in optimized liquid electrolytes deliver a large reversible capacity of over 300 mAh g-1 with two-electron V3+/V5+ cationic redox, reaching 750 Wh kg-1 versus metallic lithium. Critically, highly reversible Li storage and no capacity fading for 400 cycles were observed in all-solid-state batteries with a sulfide-based solid electrolyte. Operando synchrotron X-ray diffraction combined with high-precision dilatometry reveals excellent reversibility and a near dimensionally invariable character during electrochemical cycling, which is associated with reversible vanadium migration on lithiation and delithiation. This work demonstrates an example of an electrode/electrolyte couple that produces high-capacity and long-life batteries enabled by multi-electron transition metal redox with a structure that is near invariant during cycling.

Tracking Sub-Nano-Scale Structural Evolution in Zeolite Synthesis by In Situ High-Energy X-ray Total Scattering Measurement with Pair Distribution Function Analysis.

The crystallization mechanism of zeolites remains unclarified to date because of lack of effective techniques in characterizing the local structures of amorphous precursors under synthetic conditions. Herein, in situ high-energy X-ray total scattering measurement with pair distribution function analysis is performed throughout the hydrothermal synthesis of SSZ-13 zeolite to investigate the amorphous-to-crystalline transformation at the sub-nano level in real time. Ordered four-membered rings (4Rs) are dominantly formed during the induction period, prior to the significant increase in the number of symmetric six- and eight-membered rings (6Rs and 8Rs) in the crystal growth stage. These preformed ordered 4Rs contribute to the formation of d6r and cha composite building units containing 6Rs and 8Rs with the assistance of the organic structure-directing agent, leading to the construction of embryonic zeolite crystallites, which facilitate the crystal growth through a particle attachment pathway. This work enriches the toolbox for better understanding the crystallization pathway of zeolites.

Transient Mesoscopic Immiscibility, Viscosity Anomaly, and High Internal Pressure at the Semiconductor-Metal Transition in Liquid Ga2Te3.

Gallium tellurides appear to be promising phase-change materials (PCMs) of the next generation for brain-inspired computing and reconfigurable optical metasurfaces. They are different from the benchmark PCMs because of sp3 gallium hybridization in both cubic Ga2Te3 and amorphous pulsed laser deposition (PLD) films. Liquid Ga2Te3 also shows a viscosity η(T) anomaly just above melting when η(T) first increases and only then starts decreasing. We used high-energy X-ray diffraction to observe a transient mesoscopic immiscibility that suggested dense metallic liquid droplets in a semiconducting melt. The η(T) shape was consistent with this finding. A vanishing first sharp diffraction peak that also shifts to a higher Q indicates a high internal pressure in the metallic melt, which produces a remarkable asymmetry of the Ga-Te nearest neighbor distances and is reminiscent of high-pressure rhombohedral Ga2Te3. The observed phenomena provide a realistic scenario for a fast, multilevel SET-RESET response, which also unravels similar trends in the purported density-driven liquid polyamorphism of water, phosphorus, sulfur, and other materials.

Coordination polymer-forming liquid Cu(2-isopropylimidazolate).

The structure of the melt state of one-dimensional (1D) coordination polymer crystal Cu(isopropylimidazolate) (melting temperature T m = 143 °C) was characterized by DSC, variable temperature PXRD, solid-state NMR (SSNMR), viscoelastic measurements, XAS, and DFT-AIMD calculations. These analyses suggested "coordination polymer-forming liquid" formation with preserved coordination bonds above T m. Variable chain configurations and moderate cohesive interaction in adjacent chains are the keys to the rarely observed polymer-forming liquid. The melt structure is reminiscent of the common 1D organic polymer melts such as entanglement or random coil structures.