Simultaneous X-ray Diffraction Research Articles

Near-linear deformation behavior of quasi-Gum Metal with composition Ti-18.4Nb-1.4Zr-0.3Ta-4.3 O

A new type of Ti-18.4Nb-1.4Zr-0.3Ta-4.3O exhibiting near-linear deformation behavior was created to elucidate the core principles behind its near-linear deformation behavior in quasi-Gum Metals. The in situ simultaneous X-ray diffraction study shows that a β→α″ stress-induced martensitic transformation (SIMT) persists and covers a large stress range under the near-linear deformation of Ti-18.4Nb-1.4Zr-0.3Ta-4.3O. Within the SIMT process, the variant 5 of α″ martensite usually forms more readily as it can output the maximum phase transformation strains compared to the other equivalent variants. The experimental results indicate that near-linear deformability of quasi-Gum Metal is due to the combined influence of its inherent deformation (including elastic and trace plastic) together with a SIMT that operates over a large strain range. These findings have helped to develop a more comprehensive view of the principle behind the near-linear deformation in quasi-Gum Metals and Gum Metal.

Outstanding photocatalytic activity of a mechano-thermally synthesized Z-scheme BiFeO3- Fe2O3 heterostructure

In this study, α-Bi2O3 and α-Fe2O3 powder mixtures experienced a novel mechano-thermal procedure, which includes high-energy ball milling followed by heat treatment, resulting in the successful synthesis of a BiFeO3-Fe2O3 nanocomposite. Simultaneous thermal analysis (STA) and X-ray diffraction (XRD) showed that the formation and characteristics of BiFeO3-Fe2O3 nanocomposite are greatly influenced by the milling process, heat-treatment temperature, and the α-Bi2O3:α-Fe2O3 molar ratio. X-ray photoelectron spectroscopy (XPS) spectra confirmed the presence of Bi, Fe, and O, indicating the formation of the BiFeO3 phase. Field emission scanning electron microscopy (FESEM) analysis showed the development of plate-like microstructures in the BiFeO3 phase with an average thickness of 88 nm. Diffuse reflectance spectroscopy (DRS) indicated that the 20 h-milled nanocomposite with a molar ratio of α-Bi2O3:α-Fe2O3 (1:3) exhibited the lowest band gap of 2.38 eV after heat treatment at 750 °C. The reduction in photoluminescence (PL) peaks and increase in photocurrent in the above sample suggested a decrease in charge carrier recombination rate, leading to high photocatalytic activity of 85 and 42% for methylene blue (MB) and methyl orange (MO) degradation, respectively. The effect of various pH levels on the photocatalytic activity of both dyes was examined, with MO degrading by 94% in an acidic environment after 300 min of visible light exposure, while MB experienced similar degradation in an alkaline setting. The kinetics and mechanism of photocatalytic degradation were extensively studied using the Langmuir-Hinshelwood (L-H) model, revealing the significant role of hydroxyl radicals in photodegradation. A Z-scheme mechanism for charge transfer in the nanocomposite was postulated, drawing upon radical scavenging and Mott-Schottky experiments. The prepared photocatalyst showed excellent stability and reusability following a cyclic experiment.

Elastic anomalies across the P21mn→Pnnm structural phase transition in δ-(Al,Fe)OOH

Abstract Hydrogen may be recycled into the Earth's lower mantle by subduction and stabilized in solid solutions between phase H (MgSiO4H2), δ-AlOOH, ε-FeOOH, and SiO2 post-stishovite. In high-pressure oxyhydroxide phases, hydrogen is incorporated following the typical (OHO) sequence, adopting the asymmetric configuration O-H···O that evolves into a symmetric disordered state upon compression. Moreover these iron-/aluminum-bearing oxyhydroxides [δ-(Al,Fe)OOH] present a structural phase transition from P21nm to Pnnm as pressure increases. Here, the single-crystal elasticity of the P21nm phase of δ-(Al0.97,Fe0.03)OOH has been experimentally measured across the P21nm→Pnnm transition up to 7.94(2) GPa by simultaneous single-crystal X-ray diffraction (XRD) and Brillouin spectroscopy at high pressures. The transition appears to be continuous, and it can be described with a second, fourth and six order terms Landau potential. Our results reveal an enhanced unit-cell volume compressibility, which is linked to an increase of the b- and a-axes linear compressibility in the P21nm phase of δ-(Al0.97,Fe0.03)OOH prior to the transition. In addition, we observed the presence of elastic softening in the P21nm phase that mostly impacts the elastic stiffness coefficients c12, c22 and c23. The observed elastic anomalies cause a significant change in the pressure dependence of the adiabatic bulk modulus (KS). These results provide a better understanding of the relation between elasticity, P21mn→Pnnm structural phase transition and hydrogen dynamics in δ-(Al0.97,Fe0.03)OOH, which may be applied to other O-H···O-bearing materials.

Tracking Mn and Zn in Rechargeable Aqueous Zn-MnO2 Batteries By Operando X-Ray Absorption

Zn-MnO2 batteries with mildly acidic electrolytes are a promising chemistry for large scale storage thanks to their remarkable energy density, low cost, and high safety. This is mainly obtained thanks to the high capacity of the Zn metal anode, and the nonflammable character of the aqueous electrolyte. MnO2 is one of the most common cathode of choice, not only for being Earth-abundant, but also because it can undergo a two-electron mechanism, which is however complex and still not fully understood. There is currently agreement in considering for discharge a MnO2 dissolution, leading to soluble Mn2+ and simultaneous precipitation of Zinc Hydroxide Sulfate (ZHS, ZnSO4[Zn(OH2)]3·xH2O). When charging the process is not simply reverted. In fact, a distinct electrochemical profile is observed, with at least two distinct plateaus and a third, apparently pseudocapacitive stage (Figure 1a). A similar multistage profile is observed during the second discharge. Although such profile is characteristic and observed with different MnO2 phases and architectures, the underlying mechanism remains elusive, as it seems to involve mainly poorly crystallized phases.We studied the mechanism by operando X-ray absorption (XAS) at the Mn and Zn K-edges to follow speciation simultaneously and quantitatively in the cathode and in the electrolyte via principal component analysis. Beam intensity needed appropriate regulation to avoid interference with the experiment.Simultaneous X-ray diffraction allowed precise correlation with the MnO2 dissolution and ZHS formation. We found evidence of Mn(III) intermediate occurring during local bond reorganization, which is inferred by the significant evolution of the absorption fine structure region (EXAFS) of the Mn K-edge (Figure 1b). In contrast, minor Zn spectral changes reflect primarily processes of precipitation and dissolution, suggesting that no Zn-Mn mixed phases form during cycling. Figure 1

High-temperature interaction mechanisms of typical igniting pyrotechnics with cellulose as the packing material

In order to study the effect of cellulose shell on the thermal behavior including pyrolysis gaseous products, ignition and combustion characteristics of typical pyrotechnics, three composites of pyrotechnics/cellulose were prepared in this paper. Various characterization techniques were used to investigate the prepared composites and their combustion condensed products (CCPs), including scanning electron microscopy (SEM), simultaneous thermal analysis (DSC-TG-FTIR), X-ray diffraction (XRD), bomb calorimetry, and home-made combustion diagnostic system. The results showed that the overall heat release of the black powder and Mg/PTFE decreased from 3108 J·g−1 and 1157.4 J·g−1 to 1045.4 J·g−1 and 810.4 J·g−1 in the presence of 33.3% cellulose, respectively. Moreover, the FTIR spectra showed that the cellulose did not change the reaction pathways of black powder and Mg/PTFE, which mainly include H2O, CO2, NO2 for the black powder, and HF, H2O, CO2, CF2 for Mg/PTFE. However, the condensed products of cellulose would interact with B/KNO3 at a higher temperature, so that the heat release was largely increased by 339%. The cellulose has obviously impact on the energy release rate of Mg/PTFE in comparison to the other two composites. Moreover, the negative impact on ignition of Mg/PTFE composite is significant, when the content of cellulose reaches over 33.3%, resulting in difficult self-sustainable combustion at ambient pressure. The cellulose can largely reduce the maximum flame temperature of the black powder and Mg/PTFE, whereas it has little effect on B/KNO3. The CCPs of the involved igniting pyrotechnics and their cellulose-based composites have different phases due to their strong thermal interactions with cellulose.

Dynamic Structural Transformations in a Series of Zero-Strain Lithium-Ion Battery Materials: Almost Simultaneous Operando X-ray Diffraction and X-ray Absorption Spectroscopy on Li2ZnTi3O8 and Related Compounds

A series of Li4/3-2x/3ZnxTi5/3-x/3O4 (LZTO) with 0 ≤ x ≤ 0.5 have received considerable interest as a negative electrode material for long-cycle-life lithium-ion batteries. However, their dynamic structural transformations under operating conditions have remained unknown, making an in-depth understanding essential for further improving the electrochemical performance. We, thus, performed almost simultaneous operando X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) studies on x = 0.125, 0.375, and 0.5. The x = 0.5 sample, Li2ZnTi3O8, indicated differences in the cubic lattice parameter between the discharge and charge reactions (δacs), corresponding to the reversible movement of Zn2+ ions between the tetrahedral and octahedral sites. δac was also observed for x = 0.125 and 0.375, although the capacity region exhibiting δac decreased with a decrease in x. For all of the samples, there is no significant difference in the nearest-neighbor distance of the Ti-O bond (dTi-O) between the discharge and charge reactions. We also demonstrated different structural transformations between the micro- (XRD) and atomic (XAS) scales. In the case for x = 0.5, for instance, the maximum microscale change in ac was within +0.29(3)%, whereas at the atomic scale, dTi-O changed by up to +4.8(3)%. Combined with our previous results for ex situ XRD and operando XRD/XAS measurements on other x compositions, the whole structural nature of LZTO, such as correspondence between ac and dTi-O, origins for voltage hysteresis, and zero-strain reaction mechanisms, has been unveiled.

Asymmetric anion effects of anions in ionic liquids: Crystal polymorphs and magnetic properties

In this study, the phase transitions and magnetic properties of magnetic ionic liquids (mILs) were investigated at low temperatures. The mILs were [Cnmim]2[MnCl4-mBrm] (n = 2, 3, and 4; m = 0, 1, 2, 3, and 4), where [Cnmim]+ is 1-alkyl-3-methylimidazolium. Here, simultaneous X-ray diffraction and differential scanning calorimetry were used to determine the crystal polymorphs in the mILs. The results showed that shorter alkyl chain lengths of cations and symmetric anions aided crystallization. Melting points in [C2mim]2[MnCl4-mBrm] were also found to be strongly dependent on asymmetric anionic configurational and cationic conformational entropies. Furthermore, the asymmetric anion effect contributed slightly to the paramagnetic properties of mILs.

Sound velocities and single-crystal elasticity of hydrous Fo90 olivine to 12 GPa

Nominally anhydrous minerals (NAMs) may contain significant amounts of water and constitute an important reservoir for mantle hydrogen. The colloquial term ‘water’ in NAMs is related to the presence of hydroxyl-bearing (OH−) point defects in their crystal structure, where hydrogen is bonded to lattice oxygen and is charge-balanced by cation vacancies. This hydrous component may therefore have substantial effects on the thermoelastic parameters of NAMs, comparable to other major crystal-chemical substitutions (e.g., Fe, Al). Assessment of water concentrations in natural minerals from mantle xenoliths indicates that olivine commonly stores ∼0–200 ppm of water. However, the lack of samples originating from depths exceeding ∼250 km coupled with the rapid diffusion of hydrogen in olivine at magmatic temperatures makes the determination of the olivine water content in the upper mantle challenging. On the other hand, numerous experimental data show that, at pressures and temperatures corresponding to deep upper mantle conditions, the water storage capacity of olivine increases to 0.2–0.5 wt%. Therefore, determining the elastic properties of olivine samples with more realistic water contents for deep upper mantle conditions may help in interpreting both seismic velocity anomalies in potentially hydrous regions of Earth's mantle as well as the observed seismic velocity and density contrasts across the 410-km discontinuity.Here, we report simultaneous single-crystal X-ray diffraction and Brillouin scattering experiments at room temperature up to 11.96(2) GPa on hydrous [0.20(3) wt% H2O] Fo90 olivine to assess its full elastic tensor, and complement these results with a careful re-analysis of all the available single-crystal elasticity data from the literature for anhydrous Fo90 olivine. While the bulk (K) and shear (G) moduli of hydrous Fo90 olivine are virtually identical to those of the corresponding anhydrous phase, their pressure derivatives K′ and G′ are slightly larger, although consistent within mutual uncertainties. We then defined linear relations between the water concentration in Fo90 olivine, the elastic moduli and their pressure derivatives, which were then used to compute the sound velocities of Fo90 olivine with higher degrees of hydration. Even for water concentrations as high as 0.5 wt%, the sound wave velocities of hydrous and anhydrous olivines were found to be identical within uncertainties at pressures corresponding to the base of the upper mantle. Contrary to previous claims, our data suggest that water in olivine is not seismically detectable, at least for contents consistent with deep upper mantle conditions. In addition to that, our data reveal that the hydration of olivine is unlikely to be a key factor in reconciling seismic velocity and density contrasts across the 410-km discontinuity with a pyrolitic mantle.

In-Situ X-ray Diffraction Analysis of Metastable Austenite Containing Steels Under Mechanical Loading at a Wide Strain Rate Range

This paper presents and discusses the methodology and technical aspects of mechanical tests carried out at a wide strain rate range with simultaneous synchrotron X-ray diffraction measurements. The motivation for the study was to develop capabilities for in-situ characterization of the loading rate dependency of mechanically induced phase transformations in steels containing metastable austenite. The experiments were carried out at the DanMAX beamline of the MAX IV Laboratory, into which a custom-made tensile loading device was incorporated. The test setup was supplemented with in-situ optical imaging of the specimen, which allowed digital image correlation-based deformation analysis. All the measurement channels were synchronized to a common time basis with trigger signals between the devices as well as post-test fine tuning based on diffraction ring shape analysis. This facilitated precise correlation between the mechanical and diffraction data at strain rates up to 1 s−1 corresponding to test duration of less than one second. Diffraction data were collected at an acquisition rate of 250 Hz, which provided excellent temporal resolution. The feasibility of the methodology is demonstrated by providing novel data on the kinetics of the martensitic phase transformation in EN 1.4318-alloy following a rapid increase in strain rate (a so-called jump test).

Acoustic emission detection of micro-cracks under high pressure and high temperature in a deformation large-volume apparatus at the endstation P61B, PETRA III.

We successfully developed an in situ acoustic emission (AE) detection setup that allows recording of AE waveforms (triggered and streaming) and simultaneous x-ray diffraction and imaging on samples deformed at high pressure and high temperature (HPHT) conditions in the Aster-15 Large Volume Press at the synchrotron beamline station P61B. This high pressure AE detection system is a powerful tool to investigate AE phenomena from the HPHT chamber. Six commercial acoustic sensors, protected by a tungsten carbide support ring on each anvil of the same material, have excellent survivability throughout each successive experiment. By pulsing each sensor in succession, the average wave velocity through the anvils and cell assembly can be determined at any press load. The distance between the sensors is obtained by x-ray radiography and by logging the positions of each hydraulic ram. This provides a basis for accurately locating AE events in the sample. The feasibility of this AE detection setup was confirmed by compression and deformation test runs using several different self-designed AE sources in specialized assemblies. The present setup proves to be extremely efficient and accurate in measuring brittle processes in samples under HPHT. It is now available for applications for beam time and experiments without x rays at P61B. Combined with synchrotron x rays, in situ pressure, temperature, strain rate and stress, and phase changes can be monitored while recording AE activity. We provide a powerful tool to investigate the origin of earthquakes, for example, causing AE emissions due to brittle dehydration reactions or phase transformations in the Earth.

Shear-induced distortion of clay minerals aids in dynamic weakening of shallow faults during earthquakes

Coseismic faulting may activate complicated physicochemical processes in the fault zone through both mechanical deformation and frictional heating. While plenty of work emphasizes the great importance of thermal effects on dynamic fault weakening, less attention has been paid to the mechanochemical effects. We study the effects of mechanochemical changes of chlorite on its dynamic weakening process via low- and high-velocity friction experiments, simultaneous thermal analysis, X-ray diffraction, microstructural observation, and numerical modeling in this work. With higher degrees of deformation, the experimentally sheared chlorite samples generally show more pronounced reductions in the onset temperature of thermal decomposition (Td0; from 561°C to 189°C in the extreme case) and more striking increases in the reaction rate. The exponential-decay formula can well describe the relation between Td0 and the mechanical work (integral of shear stress with respect to displacement) in the shear deformation. Moreover, the presence of pore water and the variation in chlorite content could significantly affect the mechanochemical changes of the sheared chlorite-bearing samples. Taking the markedly lowered Td0 as the characteristic temperature leading to thermal softening of asperity contacts, numerical modeling shows that flash weakening of chlorite-rich samples can be significantly promoted, dwarfing the thermochemical pressurization that is also enhanced by mechanochemical effects though. This is largely supported by high-velocity experiments (∼m/s) performed on the pre-deformed chlorite samples, which show both lower peak friction and fracture energy, and earlier activation of dynamic weakening. Clearly, shear deformation plays a key role in aiding thermally-activated mechanisms in weakening faults and facilitating rupture propagation during earthquakes.

Simultaneous quick-scanning X-ray absorption spectroscopy and X-ray diffraction

The existing setup for time-resolved quick-scanning X-ray absorption spectroscopy (QEXAFS) at beamline P64 at the PETRA III storage ring is complemented by new infrastructure suited for the collection of X-ray diffraction data simultaneously to the QEXAFS experiment. In particular, the sinusoidal periodic movements of the quick-EXAFS mono-chromator are modified in such a way, that an energy plateau with approximately constant energy over a certain time is created in the pre-edge region of the absorption edge of interest. By employing a properly defined trigger signal in this time, the exposure of a two-dimensional X-ray detector placed behind the sample is actuated, thus allowing to collect an X-ray diffraction pattern over a certain angular range as defined by the actual X-ray energy and the position of the 2D-detector. Details of the new setup as well as exemplary results obtained during the solvothermal synthesis of ZnO nanoparticles and the bcc-fcc phase transition of iron at elevated temperatures are presented.

Effects of alkaline activators on pore structure and mechanical properties of ultrafine metakaolin geopolymers cured at room temperature

Geopolymer is a new type of green gelling and environmental protection material, but the curing temperature limits the application of geopolymer in the construction industry. In this paper, the effects of NaOH on the pore structure and mechanical properties of ultrafine metakaolin (UMK) geopolymers under room temperature curing conditions were investigated. In this experiment, different concentrations of alkaline activators were prepared by changing the concentration of NaOH in the composite alkaline activator, and geopolymers were prepared with different alkaline activators and UMK. Different UMK geopolymers have been extensively analyzed to characterize their pore distribution, pore structure, and mechanical properties. The relationship between NASH gel and NaOH concentration was quantified by simultaneous thermal analysis (TG-DTG) and X-ray diffraction (XRD). The evolution of pore distribution and pore structure of UMK geopolymers with NaOH concentration was characterized by scanning electron microscopy (SEM) and proton nuclear magnetic resonance spectroscopy (1H NMR). The results show that UMK only generates the NASH phase in the geopolymerization reaction. With the increase of sodium hydroxide concentration, the formation of NASH gel increases, and the crystallinity of the sample increases. SEM and 1H NMR results show that the UMK geopolymer prepared with a high concentration of NaOH is fully hydrated and has a dense structure. Through comparative analysis of UMK geopolymer pore distribution and pore structure characteristics, it was found that the porosity of UMK geopolymer decreased with the increase of sodium hydroxide concentration. The proportion of small pores did not change much, while the large pores gradually evolved into mesopores. In addition to this, curing time was found to have no significant effect on geopolymer microstructure and strength development. This research provides a theoretical basis for the practical engineering application of UMK.

Water-based drill cuttings, a shale gas extraction waste as supplementary cementitious material and optimization

• A method of preparing a novel supplementary cementitious material based on water-based drill cuttings was provided. • A central composite design was conducted to optimize the four factors (calcination temperature, calcination time, replacement ratio, and fineness) for WDC preparation, and optimal values were obtained. • The hardened specimens, prepared with a mixture of standard sand, ordinary Portland cement, and water-based drill cuttings, meet the compressive strength specified in ASTM-618. • The mechanisms of WDC acting in the OPC system were investigated. The water-based drill cuttings, a kind of solid waste from shale gas extraction, are examined for their utility as supplementary cementitious material. After drying, calcining, and grinding, water-based drill cuttings are expected to partially replace ordinary Portland cement for their high calcium silicate and grinding-friendly nature. A central composite design investigated four variables (calcination time, calcination temperature, replacement ratio, and fineness) for their effects on the response (compressive strength). The optimization results suggest that the best product meeting the mechanical criteria and saving energy could be obtained by replacing 10 wt% ordinary Portland cement when controlling the calcination temperature of 830–870 °C, calcination time of 28–32 min, and fineness of sieving is 1600 mesh. The compressive strength was shown to be 39.00 MPa at 7 days, 47.00 MPa at 28 days, and 52.00 MPa at 90 days. Furthermore, the mechanisms of water-based drill cuttings were characterized to confirm the feasibility of supplementary cementitious material by various analytical techniques such as X-ray fluorescence, laser particle size analyzer, simultaneous thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy.

Cellulose lattice strains and stress transfer in native and delignified wood

Small specimens of spruce wood with different degrees of delignification were studied using in-situ tensile tests and simultaneous synchrotron X-ray diffraction to reveal the effect of delignification and densification on their tensile properties at relative humidities of 70–80 %. In addition to mechanical properties, these analyses yield the ratio of strains in the cellulose crystals and in the bulk, which reflects the stress-transfer to crystalline cellulose. While the specific modulus of elasticity slightly increases from native wood by partial or complete delignification, the lattice strain ratio does not show a significant change. This could indicate a compensatory effect from the decomposition of the amorphous matrix by delignification and from a tighter packing of cellulose crystals that would increase the stress transfer. The reduced strain to failure and maximum lattice strain of delignified specimens suggests that the removal of lignin affects the stress-strain behavior with fracture at lower strain levels.

Fluorosubstitution of the Molecular Core in Chiral Esters with Short Terminal Carbon Chains: Influence on Physical Properties

Comparative study of chiral liquid crystalline (S)-(1)-4’-(1-methylheptylcarbonyl) biphenyl-4-yl 4-[4-(2,2,3,3,4,4,4-heptafluorobutoxy)butyl-1-oxy] benzoate (4HH) and (S)-4’-(1-methylheptyloxycarbonyl)biphenyl-4-yl 4-[4-(2,2,3,3,4,4,4-heptafluorobutoxy) butyl-1-oxy]-2,3-difluorobenzoate (4FF) is performed by complementary methods. For 4HH melting of the low-temperature crystal phase and subsequent cold crystallization (from antiferroelectric smectic CA* phase to the high-temperature crystal phase) are reported, crystallization kinetics is examined and a monotropic hexatic SmXA* phase is observed on cooling. For 4FF rich polymorphism in the solid state is investigated mainly by simultaneous X-ray diffraction and differential scanning calorimetry measurements. Influence of fluorosubstitution on structural, electro-optic and dielectric properties of the smectic phases is reported. Unit cell parameters of crystal phases of 4HH and 4FF are determined. The reported results show that the double fluorosubstitution slows down the Goldstone mode and PH phason in the smectic phases and facilitates crystallization.

High energy X-ray diffraction and small-angle scattering measurements of hydrogen fatigue damage in AISI 4130 steel

Accurate lifetime predictions are critical for repurposing existing pipelines for hydrogen transmission as well as for developing novel steels which are minimally susceptible to lifetime degradation by hydrogen. Ultimately, lifetime prediction models assess the amount of damage a material undergoes during a typical service cycle and the cumulative damage a material can withstand prior to failure. However, not all damage processes are equal, and neither is the manner in which mechanical loading translates to damage the same when materials are in inert environments compared to in hydrogen environments. For example, in the three leading proposed mechanisms of hydrogen embrittlement (Hydrogen-Enhanced Decohesion (HEDE), the Hydrogen-Enhanced Localized Plasticity (HELP), and the Nano-Void Coalescence (NVC)), hydrogen is proposed to enhance the manifestation of grain separation, dislocation generation/movement, and void coalescence, respectively. A full understanding of the damage modes requires a measurement capable of probing all three mechanisms at once. Here we present simultaneous High Energy X-ray Diffraction (HEXRD) and Small-Angle X-ray Scattering (SAXS) during fatiguing of steel in hydrogen. HEXRD measurements probe strain and dislocation density; SAXS measurements probe nano-pore generation and coalescence. We will discuss the differences in damage modes between steels fatigued in air and in hydrogen and the role these difference play in lifetime predictions.

Simultaneous imaging and diffraction in the dynamic diamond anvil cell.

The ability to visualize a sample undergoing a pressure-induced phase transition allows for the determination of kinetic parameters, such as the nucleation and growth rates of the high-pressure phase. For samples that are opaque to visible light (such as metallic systems), it is necessary to rely on x-ray imaging methods for sample visualization. Here, we present an experimental platform developed at beamline P02.2 at the PETRA III synchrotron radiation source, which is capable of performing simultaneous x-ray imaging and diffraction of samples that are dynamically compressed in piezo-driven diamond anvil cells. This setup utilizes a partially coherent monochromatic x-ray beam to perform lensless phase contrast imaging, which can be carried out using either a parallel- or focused-beam configuration. The capabilities of this platform are illustrated by experiments on dynamically compressed Ga and Ar. Melting and solidification were identified based on the observation of solid/liquid phase boundaries in the x-ray images and corresponding changes in the x-ray diffraction patterns collected during the transition, with significant edge enhancement observed in the x-ray images collected using the focused-beam. These results highlight the suitability of this technique for a variety of purposes, including melt curve determination.

XFEL serial crystallography reveals the room temperature structure of methyl-coenzyme M reductase

Methyl-Coenzyme M Reductase (MCR) catalyzes the biosynthesis of methane in methanogenic archaea, using a catalytic Ni-centered Cofactor F430 in its active site. It also catalyzes the reverse reaction, that is, the anaerobic activation and oxidation, including the cleavage of the CH bond in methane. Because methanogenesis is the major source of methane on earth, understanding the reaction mechanism of this enzyme can have massive implications in global energy balances. While recent publications have proposed a radical-based catalytic mechanism as well as novel sulfonate-based binding modes of MCR for its native substrates, the structure of the active state of MCR, as well as a complete characterization of the reaction, remain elusive. Previous attempts to structurally characterize the active MCR-Ni(I) state have been unsuccessful due to oxidation of the redox- sensitive catalytic Ni center. Further, while many cryo structures of the inactive Ni(II)-enzyme in various substrates-bound forms have been published, no room temperature structures have been reported, and the structure and mechanism of MCR under physiologically relevant conditions is not known. In this study, we report the first room temperature structure of the MCRred1-silent Ni(II) form using an X-ray Free-Electron Laser (XFEL), with simultaneous X-ray Emission Spectroscopy (XES) and X-ray Diffraction (XRD) data collection. In celebration of the seminal contributions of inorganic chemist Dick Holm to our understanding of nickel-based catalysis, we are honored to announce our findings in this special issue dedicated to this remarkable pioneer of bioinorganic chemistry.

Tuning the Morphology in the Nanoscale of NH4CN Polymers Synthesized by Microwave Radiation: A Comparative Study.

A systematic study is presented to explore the NH4CN polymerization induced by microwave (MW) radiation, keeping in mind the recent growing interest in these polymers in material science. Thus, a first approach through two series, varying the reaction times and the temperatures between 130 and 205 °C, was conducted. As a relevant outcome, using particular reaction conditions, polymer conversions similar to those obtained by means of conventional thermal methods were achieved, with the advantage of a very significant reduction of the reaction times. The structural properties of the end products were evaluated using compositional data, spectroscopic measurements, simultaneous thermal analysis (STA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). As a result, based on the principal component analysis (PCA) from the main experimental results collected, practically only the crystallographic features and the morphologies in the nanoscale were affected by the MW-driven polymerization conditions with respect to those obtained by classical syntheses. Therefore, MW radiation allows us to tune the morphology, size and shape of the particles from the bidimensional C=N networks which are characteristic of the NH4CN polymers by an easy, fast, low-cost and green-solvent production. These new insights make these macromolecular systems attractive for exploration in current soft-matter science.