Time-resolved Synchrotron X-ray Research Articles

Dehydration kinetics of nanoconfined water in beryl probed by high temperature single crystal synchrotron X-ray diffraction

Understanding changes in material properties through external stimuli plays a key role in validating the expected performance of materials and engineering material properties in a controlled manner. Here, we introduce a fundamental protocol to deduce dehydration reactions kinetics of water confined in nanopore channels, with the cyclosilicate beryl as the scaffold of interest, using time-resolved synchrotron X-ray diffraction (SXRD), in the temperature interval of 298–1038 K. The temperature-dependent intensity (I)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(I)$$\\end{document} of the strongest reflection (112) was used as the crystallite variable. An estimation of an isobaric thermal crystallite coefficient, k\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$k$$\\end{document}, analogous with the isobaric thermal expansion coefficient, established the rate of relative crystallization as a function of temperature, ∂I∂T\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\frac{\\partial I}{\\partial T}$$\\end{document}. A plot of lnk\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$lnk$$\\end{document} and 1T\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\frac{1}{T}$$\\end{document} gives rise to two kinetic steps, indicating a slow dehydration stage up to ~ 700 K and a fast dehydration stage up to the investigated temperature 1038 K. The crystal structure of beryl determined up to 1038 K, in temperature increment as small as 10 K, indicates the presence of channel ions Na and Fe and a gradual decrease of water upon heating.

(Invited) Pulsed Neutron and Synchrotron X-Ray Imaging of Liquid Water Formation and Transport in Polymer Electrolyte Fuel Cells

Fuel-cell electric vehicles (FCEVs) powered by hydrogen are expected to be the ultimate eco-friendly cars, and so developing low-cost, high-performance, and highly reliable FCEVs is strongly demanded. Polymer electrolyte fuel cells (PEFCs) consist of an electrolyte membrane sandwiched between an anode and a cathode, where both the anode and cathode have laminated structures composed of a catalyst-coated membrane (CCM) and gas channels in contact with a gas diffusion layer (GDL). The GDL consists of a microporous layer (MPL) and a substrate. One problem with PEFCs is that liquid water generated as a by-product of the electrochemical reaction at the catalyst accumulates in the GDL, and prevents oxygen from being transported through the gas channels to the catalyst. Therefore, to achieve a high power density, it is necessary to develop new materials and optimize the design of the gas channel to discharge water from the cathode to the exterior of the cell. We are currently constructing a multiscale analysis methodology that combines quantum beam analysis using X-rays and neutrons to clarify water behavior in a PEFC [1-9].In this presentation, we introduce three topics related to water behavior on scales ranging from several micrometers (pores in GDLs) to hundreds of millimeters (automotive fuel cells). The first topic concerns imaging the liquid water distribution in an MPL [2, 6]. The imaging analysis was performed using time-resolved synchrotron X-ray computed tomography while water vapor was supplied to the MPL side of the GDL. With increasing exposure to water vapor, the average volume of wet domains in the MPL initially increased, whereas the overall number of such domains decreased. This implies that wet domains expand by absorbing water vapor and combining with each other. As the exposure to water vapor was further increased, the volume fraction of wet domains in the MPL reached a steady state, indicating that liquid water was discharged to the outer surface of the MPL and to the substrate side. The second topic is obtaining mechanistic insights into water behavior in a subscale PEFC [8]. Time-resolved operando synchrotron X-ray radiography to determine the effects of temperature and relative humidity on the condensation and transport of water in PEFCs. The results show that condensation and transport to the channel can be classified into four categories: 1) concurrent liquid and vapor transport, 2) mainly liquid transport, 3) vapor transport, and 4) accumulation near the ribs. X-ray imaging experiments were conducted at the TOYOTA Beamline (BL33XU) at the SPring-8 facility. The third topic is operando neutron imaging of the water distribution and identifying water/ice phases in large automotive PEFCs during a cold start. We developed an experimental system using a pulsed spallation neutron beam at the RADEN instrument at BL22 of the Materials and Life Science Experimental Facility (MLF) in the Japan Proton Accelerator Research Complex (J-PARC). The results showed direct evidence of stepwise freezing inside the PEFC. The water initially accumulated in the center of the PEFC and began to freeze, and this was followed by PEFC shutdown as freezing progressed. We defined the time interval between the beginning of freezing and shutdown as the “extended time”. This is expected to be useful as an indicator for optimizing the cold-start protocol, cell design, and choice of material.Reference1) Y. Nagai, J. Eller, T. Hatanaka, S. Yamaguchi, S. Kato, A. Kato, F. Marone, H. Xu and F. N. Büchi, J. Power Sources, 435 (2019) 226809.2) S. Kato, S. Yamaguchi, W. Yoshimune, Y. Matsuoka, A. Kato, Y. Nagai and T. Suzuki, Electrochem. Commun., 111 (2020) 106644.3) S. Yamaguchi, S. Kato, A. Kato, Y. Matsuoka, Y. Nagai and T. Suzuki, Electrochem. Commun., 128 (2021) 107059.4) Y. Higuchi, D. Setoyama, K. Isegawa, Y. Tsuchikawa, Y. Matsumoto, J. D. Parker, T. Shinohara and Y. Nagai, Phys. Chem. Chem. Phys., 23 (2021) 1062-10715) S. Yamaguchi, S. Kato, W. Yoshimune, D. Setoyama, A. Kato, Y. Nagai, T. Suzuki, A. Takeuchi and K. Uesugi, J. Synchrotron Radiat., 29 (2022) 1258-1264.6) S. Kato, S. Yamaguchi, Y. Matsuoka, A. Kato, T. Suzuki and Y. Nagai, InterPore2022, Book of s, p139.7) K. Isegawa, D. Setoyama, Y. Higuchi, Y. Matsumoto, Y. Nagai and T. Shinohara, Nucl. Instrum. Methods Phys. Res. A 1040, 167260 (2022).8) A. Kato, S. Kato, S. Yamaguchi, T. Suzuki and Y. Nagai, J. Power Sources, 521 (2022), 230951.9) Y. Higuchi, W. Yoshimune, S. Kato, S. Hibi, D. Setoyama, K. Isegawa, Y. Matsumoto, H. Hayashida, H. Nozaki, M. Harada, N. Fukaya, T. Suzuki, T. Shinohara and Y. Nagai, to be submitted.

Real-Time Atomic Scale Kinetics of a Dynamic Event in a Model Ionic Crystal

The mineral CaF2 is the archetype of the α fluorite structure and its high-pressure phase transition to γ cotunnite is an ideal test bed for exploring the effects of kinetics. The inter-disciplinary topic of the kinetics of dynamically driven phase transitions is at the forefront of condensed matter physics, both for its theoretical importance and its relevance to technological applications at extreme conditions of pressure and temperature. Here we probe the α → γ → α structural transformations taking place over the nanosecond timescale of a dynamic event, beginning-to-end: from the principal shock Hugoniot state, followed by a quasi-steady off-Hugoniot release state, and finally the unsteady return to near-ambient conditions. We present quantitative, atomic-scale data of the unfolding of the dynamically driven phase transition and its subsequent reversal close to the α/γ phase boundary. Dynamic loading with a two-stage gas gun is coupled with in situ time-resolved synchrotron X-ray diffraction and with continuum scale velocimetry at the Dynamic Compression Sector (DCS), Advanced Photon Source, Argonne National Laboratory. Our results demonstrate the time dependence of phase transitions and highlight the need for modeling of transition kinetics in dynamically driven processes.

Effect of grain size on amorphization mechanism and kinetics of bridgmanite in shocked meteorites

Bridgmanite formation and amorphization in shocked meteorites constrain the pressure and temperature conditions during planetary impact. However, the effect of the bridgmanite grain size on its amorphization kinetics is still unclear. Here, the amorphization mechanism and kinetics of fine-grained polycrystalline bridgmanite were studied at high temperatures up to 1080 K. High-temperature time-resolved synchrotron X-ray diffraction measurements showed that significant volume expansion due to temperature-induced amorphization caused static stress, which then hindered amorphization progress. Further, the temperature required for the amorphization of fine-grained bridgmanite (~ 1 μm) was found to be approximately 100 K higher than that required for the amorphization of coarse-grained samples (> 10 μm). We also noted that amorphization preferentially commenced at the twin planes and subgrain boundaries of bridgmanite grains, resulting in lower amorphization temperatures for the coarse-grained samples. The limited number of such specific locations in fine-grained natural bridgmanite suggested that grain boundary amorphization may be the dominant mechanism for bridgmanite amorphization in shocked meteorites. This unique amorphization kinetics would support the preservation of bridgmanite during the post-shock annealing in the shocked meteorite. Although bridgmanite amorphization starts easily at temperatures above ~ 420 K, a small amount of bridgmanite grains can survive at temperatures above 800 K by the effect of amorphization-induced stress.

Photocarrier transport of ferroelectric photovoltaic thin films detected by the magnetic dynamics of adjacent ferromagnetic layers

We have observed photocarrier transport behaviors in ${\mathrm{BiFeO}}_{3}/{\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{MnO}}_{3}$ (BFO/LSMO) heterostructures by using time-resolved synchrotron x-ray magnetic circular dichroism in reflectivity. The magnetization of LSMO layers was used as a probe of photo-induced carrier dynamics in the photovoltaic BFO layers. During the photo-induced demagnetization process, the decay time of LSMO ($x$=0.2) magnetization strongly depends on the ferroelectric polarization direction of the BFO layer. The variation of decay time should be attributed to the different sign of accumulated photocarriers at the BFO/LSMO interface induced by the photovoltaic effect of the BFO layer. The photocarriers can reach the BFO/LSMO interface and influence the magnetization distribution in the LSMO layers within the timescale of $\ensuremath{\sim}100$ ps. Our results provide a novel strategy to investigate carrier dynamics and mechanisms of optical control of magnetization in thin film heterostructures.

Emergence of Dynamically-Disordered Phases During Fast Oxygen Deintercalation Reaction of Layered Perovskite.

Determination of a reaction pathway is an important issue for the optimization of reactions. However, reactions in solid-state compounds have remained poorly understood because of their complexity and technical limitations. Here, using state-of-the-art high-speed time-resolved synchrotron X-ray techniques, the topochemical solid-gas reduction mechanisms in layered perovskite Sr3 Fe2 O7- δ (from δ ∼ 0.4 to δ = 1.0), which is promising for an environmental catalyst material is revealed. Pristine Sr3 Fe2 O7- δ shows a gradual single-phase structural evolution during reduction, indicating that the reaction continuously proceeds through thermodynamically stable phases. In contrast, a nonequilibrium dynamically-disordered phase emerges a few seconds before a first-order transition during the reduction of a Pd-loaded sample. This drastic change in the reaction pathway can be explained by a change in the rate-determining step. The synchrotron X-ray technique can be applied to various solid-gas reactions and provides an opportunity for gaining a better understanding and optimizing reactions in solid-state compounds.

Application of Time-Resolved Synchrotron X-ray Absorption Spectroscopy in an Energy Conversion Reaction

The rational design of high-efficiency catalysts is hindered by the knowledge of active sites, which always experience dynamic transformations within different time scales. In this regard, tracking these time-dependent processes is essential to building the correlation between the active site and catalytic performance. Achieving this goal requires powerful characterization techniques to overcome the obstacle induced by the time mismatch. By virtue of the local structure sensitivity, synchrotron X-ray absorption spectroscopy (XAS) comprising step-scanning XAS, quick-scanning XAS, and energy-dispersive XAS has been widely applied to record structural evolution events. In this Perspective, we highlight the substantial accomplishments achieved by these time-resolved XAS techniques. Their principles, advantages, and limitations involved in monitoring energy-involving electrocatalysis were also introduced. Meanwhile, the key challenges that we are encountering and the further directions of time-resolved XAS are also provided. We sincerely hope that these insights could offer a reliable guideline for other researchers to design more efficient in situ experiments.

Dynamic electrical response of vortex polarization in (Pb0.9Sr0.1)TiO3/SrTiO3 artificial superlattice thin films

Artificial superlattice thin films with alternative Pb0.9Sr0.1TiO3 (PST) and SrTiO3 layers were fabricated via pulsed laser deposition. The vortex domains were formed by adjusting the unit cell number of the PST layer to be 20. The electrical response measured by time-resolved synchrotron x-ray diffraction with the repeated pulse voltages of a time interval of 1000 μs indicates that the reorientation of dipole moments in the vortex domains is susceptible to the applied electric field and is a reversible process. Although the centrosymmetric vortex domain structure is not considered to exhibit piezoelectricity, an evident change in the out-of-plane lattice constant with the applied electric field was confirmed. The magnitude of the electromechanical response at 600 kV/cm was estimated to be 19 pm/V, which is nearly comparable to the piezoelectric constant d33 of bulk PbTiO3.

Hematite-goethite ratios at pH 2–13 and 25–170 °C: A time-resolved synchrotron X-ray diffraction study

Iron (oxyhydr)oxides are sensitive indicators of pH, Eh, temperature, microbial activity, and climate conditions in the Critical Zone. The most ubiquitous and environmentally significant iron oxides in most soils are two-line ferrihydrite, goethite, and hematite. Here we present a comprehensive study of the transformation of two-line ferrihydrite to hematite and goethite over a wide range of temperature (25–170 °C) and initial pH (2−13) conditions through ex situ batch and in situ synchrotron X-ray diffraction (XRD) experiments.Within the high time resolution of our experiments, goethite and hematite nucleated nearly simultaneously from ferrihydrite in nearly equal concentrations by mass. Hematite increased in abundance relative to goethite until a steady-state ratio was achieved, and both phases ceased growth on the depletion of ferrihydrite. Higher temperatures and lower water activities favored hematite formation at all pH values studied. In both our batch and our time-resolved, angle-dispersive synchrotron X-ray diffraction experiments, hematite was favored relative to goethite at an initial pH of 3 to 5. In contrast, goethite preferentially formed in neutral (initial pH 7–8) and highly alkaline conditions (initial pH ≥ 11). Surprisingly, mildly alkaline conditions (initial pH 9–11) induced the precipitation of a highly Fe-deficient (Feocc = ~0.80–0.90) variety of hematite known as “hydrohematite” in greater concentrations than goethite. Our results are useful for the application of hematite-goethite ratios as paleoclimate proxies for soil and sediment systems with low pH buffering capacities.

Revealing structure-selectivity correlations in pulsed CO2 electrolysis via time-resolved operando synchrotron X-ray studies

Revealing structure-selectivity correlations in pulsed CO2 electrolysis via time-resolved operando synchrotron X-ray studies

In Situ Visualization of Local Distortions in the High-Tc Molecule-Intercalated Lix(C5H5N)yFe2-zSe2 Superconductor.

A time-resolved synchrotron X-ray total scattering study sheds light on the evolution of the different structural length scales involved during the intercalation of the layered iron-selenide host by organic molecular donors, aiming at the formation of the expanded-lattice Lix(C5H5N)yFe2-zSe2 hybrid superconductor. The intercalates are found to crystallize in the tetragonal ThCr2Si2-type structure at the average level, however, with an enhanced interlayer iron-selenide spacing (d = 16.2 Å) that accommodates the heterocyclic molecular spacers. Quantitative atomic pair distribution function (PDF) analysis at variable times suggests distorted FeSe4 tetrahedral local environments that appear swollen with respect to those in the parent β-FeSe. Simultaneously acquired in situ synchrotron X-ray powder diffraction data disclose that secondary phases (α-Fe and Li2Se) grow significantly when a higher lithium concentration is used in the solvothermal reaction or when the solution is aged. These observations are in line with the strongly reducing character of the intercalation medium's solvated electrons that mediate the defect chemistry of the expanded-lattice superconductor. In the latter, intralayer correlated local distortions indicate electron-donating aspects that reflect in somewhat enlarged Fe-Se bonds. They also reveal a degree of relief of chemical pressure associated with a large distance between Fe and Se sheets ("taller" anion height) and a stretched Fe-Fe square planar topology. The elongation of the latter, derived from the in situ PDF study, speaks for a plausible increase in the Fe-site vacancy concentration. The evolution of the local structural parameters suggests an optimum reaction window where kinetically stabilized phases resemble the distortions of the edge-sharing Fe-Se tetrahedra, required for a high-Tc in expanded-lattice iron-chalcogenides.

Mechanistic insights into water transport in polymer electrolyte fuel cells with a variation of cell temperature and relative humidity of inlet gas elucidated by operando synchrotron X-ray radiography

Excessive liquid water in the gas diffusion layer (GDL) of polymer electrolyte fuel cells (PEFCs) is known to degrade their performance. PEFCs for automotive applications are required to work over a broad temperature range and over a wide range of relative humidity (RH) levels of the gas in their channels. Time-resolved operando synchrotron X-ray radiography was used to understand the effect of temperature and RH on the condensation and transport of water in PEFCs. The results show that the type of condensation and transport to the channel can be classified into four categories on the basis of the transient behavior of the liquid water distribution. The first category is concurrent liquid and vapor transport, the second is liquid-transport dominated, the third is vapor-only transport, and the fourth is accumulation-only near the ribs. We propose the possibility of oversaturation in the GDL, which is usually not considered in numerical calculations of the water distribution in PEFCs. We also show the possibility that experimental results are inconsistent with continuous water distribution in the in-plane direction, which is predicted under the assumption that the GDL structure is uniform and that capillary pressure transports liquid water in the GDL.

Dynamic Tilting of Ferroelectric Domain Walls Caused by Optically Induced Electronic Screening.

Optical excitation perturbs the balance of phenomena selecting the tilt orientation of domain walls within ferroelectric thin films. The high carrier density induced in a low-strain BaTiO_{3} thin film by an above-band-gap ultrafast optical pulse changes the tilt angle that 90° a/c domain walls form with respect to the substrate-film interface. The dynamics of the changes are apparent in time-resolved synchrotron x-ray scattering studies of the domain diffuse scattering. Tilting occurs at 298K, a temperature at which the a/b and a/c domain phases coexist but is absent at 343K in the better ordered single-phase a/c regime. Phase coexistence at 298K leads to increased domain-wall charge density, and thus a larger screening effect than in the single-phase regime. The screening mechanism points to new directions for the manipulation of nanoscale ferroelectricity.

Composition-Driven Structural Modulation and Guest-Induced Nanotemplate Effects of the Host–Guest Complexes Made by a Unimolecular Q-Clip

The composition of a self-assembly system has long been an essential factor that governs the resulting supramolecular structures. Nevertheless, due to the rigorous demands of structural compatibility in host–guest chemistry, the molar ratio of host–guest mixtures has not been applied as a significant factor in modulating the supramolecular structures of host–guest complexes. In this study, via using a novel unimolecular quaternary clip (Q-clip) as the host molecule and pyrene as the guest molecule and a nanotemplating reagent, we discovered that the changes in the molar ratios of the Q-clip:pyrene mixtures resulted in the structural modulation of the host–guest complexes. Supramolecular lamellae made by the 1:4 Q-clip:pyrene mixture and a hexagonal columnar phase (Colh) made by the 1:8 Q-clip:pyrene mixture were identified by the 1D powder and 2D fiber WAXS characterizations. Time-resolved synchrotron X-ray characterization and thermal analysis further showed that removing the easily sublimed guest molecules (pyrene) via thermal annealing simply hollowed out the supramolecular structures without damaging the supramolecular scaffolds made by the Q-clips. Pyrene is thus a nanotemplating reagent that can be used to create the hollowed-out 2D lamellar and 1D cylindrical scaffolds of Q-clips. The study thus gave a novel example of a host–guest mixture that is able to carry out composition-driven structural modulation and guest-induced nanotemplates. The finding broadens the horizon of host–guest chemistry and may inspire more nanoinnovation.

Fast in-situ X-ray scattering reveals stress sensitivity of gypsum dehydration kinetics

The dehydration of gypsum to hemihydrate has been studied for decades because it is an important model reaction for understanding fluid-triggered earthquakes, and due to the global use of plaster of Paris in the construction industry. The dehydration kinetics of gypsum strongly depend on temperature and water vapour pressure. Here, we perform fast, time-resolved synchrotron X-ray scattering on natural alabaster samples, finding that a small elastic load accelerates the dehydration reaction significantly. The mechanical acceleration of the reaction consumes about 10,000 times less energy than that due to heating. We propose that this thermodynamically surprising finding is caused by geometry-energy interactions in the microstructure, which facilitate nucleation and growth of the new crystalline phase. Our results open research avenues on the fundamental thermo-mechanics of crystal hydrates and the interaction of stress and chemical reactions in crystalline solids with a wide range of implications, from understanding dehydration-triggered earthquakes to the energy-efficient design of calcination processes.

Four-dimensional imaging and free-energy analysis of sudden pore-filling events in wicking of yarns.

What are the mechanisms at play in the spontaneous imbibition dynamics in polyethylene terephthalate filament yarns at pore scale? Processes at pore scale such as waiting times between the filling of two neighboring pores, as observed in special irregular porous media, like yarns, may overrule the predicted behavior by well-known laws such as Washburn's law. While the imbibition physics are well known, classic models like Washburn's law cannot explain the dynamics observed for yarns. The stepwise dynamics is discussed in terms of the interplay of thermodynamic free energy and viscous dissipation. Time-resolved synchrotron x-ray microtomography documents water filling at pore scale. Spontaneous imbibition in yarns is characterized by a series of fast pore-filling events separated by long periods of low flux. Four-dimensional imaging allows the extraction of interface areas at the boundaries between water, air, and polymer and the calculation of free-energy evolution. It is found that the waiting periods correspond to quasistable water configurations of almost vanishing free-energy gradient. The distributions of pore filling event sizes and waiting times spread over several orders of magnitude, resulting in the pronounced stepwise uptake dynamics.

Developing a system for in vivo imaging of maize roots containing iodinated contrast media in soil using synchrotron XCT and XRF

AimsWe sought to develop a novel experimental system which enabled application of iodinated contrast media to in vivo plant roots intact in soil and was compatible with time-resolved synchrotron X-ray computed tomography imaging. The system was developed to overcome issues of low contrast to noise within X-ray computed tomography images of plant roots and soil environments, the latter of which can complicate image processing and result in the loss of anatomical information.MethodsTo demonstrate the efficacy of the system we employ the novel use of both synchrotron X-ray computed tomography and synchrotron X-ray fluorescence mapping to capture the translocation of the contrast media through root vasculature into the leaves.ResultsWith the application of contrast media we identify fluid flow in root vasculature and visualise anatomical features, which are otherwise often only observable in ex vivo microscopy, including: the xylem, metaxylem, pith, fibres in aerenchyma and leaf venation. We are also able to observe interactions between aerenchyma cross sectional area and solute transport in the root vasculature with depth.ConclusionsOur novel system was capable of successfully delivering sufficient contrast media into root and leaf tissues such that anatomical features could be visualised and internal fluid transport observed. We propose that our system could be used in future to study internal plant transport mechanisms and parameterise models for fluid flow in plants.

Disorder trapping and formation of antiphase nanodomains in Ni3Sn: In situ observation and high resolution characterization

Rapid solidification of the intermetallic Ni3Sn compound from an undercooled liquid was investigated using time-resolved synchrotron X-ray diffraction. Primary growth of an ordered and a disordered cubic solid was observed in situ at a low and a high undercooling, respectively. The disordered cubic solid was reordered after rapid solidification and experienced a solid-state transformation in cooling. A HRTEM study revealed high density of crystal defects and nanodomains in the transformed matrix. A HAADF-STEM study determined that the nanodomains are antiphase domains with chemical disorder. These observations indicated a possibility of online control of mechanical properties in additively manufactured intermetallics.

Design and Precursor-based Solid-State Synthesis of Mixed-Linker Zr-MIL-140A.

Acetic acid, an alternative green solvent, was utilized for the solvothermal synthesis of four 2D materials of composition [Zr2O2(OAc)2(BDC-F)], [Zr2O2(OAc)2(BDC-F4)], [Zr2O2(OAc)2(BDC)], and [Zr2O2(OAc)2(NDC)] (BDC, terephthalate; BDC-F, 2-fluoroterephthalate; BDC-F4, tetrafluoroterephthalate; NDC, 2,6-naphthalenedicarboxylate). The first three compounds were subsequently reacted with terephthalic acid in solid-state reactions to form porous MIL-140A-type metal-organic frameworks and mixed-linker derivatives ([ZrO(BDC)1-x(BDC-Y)x], x = 0-0.18, Y = F, F4). The reaction kinetics of the formation of MIL-140A were investigated with the aid of time-resolved synchrotron and temperature-resolved in-house X-ray powder diffraction experiments. Thorough compositional analyses and solid-state NMR spectroscopic experiments were used to assess the crystallographic ordering of the different linker molecules. Additionally, acetic acid-based routes for the direct synthesis of MIL-140A-NO2 and a novel MIL-140A-(CH3)2 derivative were discovered.

Consequences of sp2–sp3 boron isomerization in supercooled liquid borates

Time-resolved high-energy synchrotron x-ray total scattering measurements on supercooled molten lithium metaborate (LiBO2) reveal an isomerization reaction involving conversion of trigonal sp2 boron to tetrahedral sp3 boron during quenching and glass formation. Van't Hoff analysis yields an accurate enthalpy change, ΔH = 21(1) kJ mol−1 boron, from which we develop an analytical model for the sp3 isomer fraction and its contribution to configurational heat capacity (Cpconf) and entropy as a function of temperature and composition. Isomerization constitutes 40% of the total calorimetric Cpconf at the glass transition for LiBO2 and directly contributes to the observed rise in liquid fragility with the lithium content.