Synchrotron X-ray Research Articles

Suppression of Ferroelectric Transitions by Symmetry Trapping in Dion-Jacobson-Layered Perovskites Cs(La,Nd)Nb2O7.

CsNdNb2O7 is a hybrid improper ferroelectric (HIF) where oxygen octahedral rotation modes induce spontaneous polarization. While CsLaNb2O7 is also believed to be an HIF, its polar structure and ferroelectric properties remain poorly understood. This study investigates their solid solution, CsLa1-xNdxNb2O7, by constructing a temperature-composition phase diagram using synchrotron X-ray diffractometry, first-principles calculations, and dielectric measurements. Upon cooling, the Nd-rich compositions (x = 0.5, 0.75, and 1) undergo phase transitions from a P4/mmm to a C2/m and then to a polar P21am phase. Both transition temperatures decrease as x decreases. The polar P21am phase, accompanied by ferroelectric polarization switching, is stabilized at room temperature only when x = 0.75 and 1. For La-rich compositions, the nonpolar C2/m phase remains down to room temperature without exhibiting any indication of transformation into the polar P21am phase. Theoretical calculations suggest that a symmetry trapping effect hinders the nonpolar (C2/m)-to-polar (P21am) phase transition.

Single crystalline, Non-stoichiometric Hydrogen-bonded Organic Frameworks Showing Versatile Fluorescence Depending on Composition Ratios and Distributions.

We report on the synthesis, characterization and photobehavior of single crystalline non-stoichiometric hydrogen-bonded organic frameworks (NS-HOFs). NS-HOFs (BTNT-1) with various composition ratios were successfully obtained as single crystals from two analogue tetratopic carboxylic acids, possessing naphthalene and benzothiadiazole cores NTTA and BTTA, respectively. The heterogeneous distribution of the components was thoroughly confirmed by time-resolved fluorescence microscopy and focused synchrotron X-ray radiation techniques, for the first time. The versatile fluorescence of BTNT-1 behavior depends on the composition ratio and distribution of the component in the single crystals. We observed not only fluorescence bands with various colors such as purple, blue, green and white, depending on the composition ratio of both components in BTNT-1, but also different emission bands from a single crystal. Furthermore, we provide details on their emission lifetimes following the composition, emission color and targeted region on the crystal. These results demonstrate unique and versatile optical properties of carboxylic acid-based NS-HOFs and provide a concept of creating functional mixed porous materials capable of different and tunable optical properties.

Toxic, radioactive, and disordered: a total scattering study of TlTcO4.

A detailed variable temperature neutron total scattering study of the potential nuclear waste matrix TlTcO4 was conducted. The long-range average structure of TlTcO4 undergoes an orthorhombic Pnma to tetragonal I41/amd phase transition below 600 K, consistent with previous synchrotron X-ray diffraction studies. However, several anomalies were observed in the Rietveld refinements to the neutron powder diffraction data, such as large atomic displacement parameters at low temperature and a shortening of the Tc-O bond distance upon heating. Modelling the short-range local structure of both the low- and high-temperature data required a lowering of symmetry to the monoclinic P21/c model due to the stereochemical activity of the Tl+ 6s2 lone pairs. Density functional theory calculations also verified this model to have a lower ground state energy than the corresponding long-range average structure. It is concluded that at low temperatures, the Tl+ 6s2 lone pairs are 'frozen' into the structure. Upon heating, the rigid TcO4 tetrahedra begin to rotate, as governed by the Γ3+ and M4+ modes. However, there is a disconnect between the two length scales, with the 6s2 lone pair electrons remaining stereochemically active on the local scale, as observed in the neutron pair distribution function fits. The orthorhombic Pnma to tetragonal I41/amd phase transition is seemingly the result of a change in the correlation length of the Tl+ 6s2 lone pairs, leading to a larger unit cell volume due to their uncorrelated displacements.

A self-healing plastic ceramic electrolyte by an aprotic dynamic polymer network for lithium metal batteries.

Oxide ceramic electrolytes (OCEs) have great potential for solid-state lithium metal (Li0) battery applications because, in theory, their high elastic modulus provides better resistance to Li0 dendrite growth. However, in practice, OCEs can hardly survive critical current densities higher than 1 mA/cm2. Key issues that contribute to the breakdown of OCEs include Li0 penetration promoted by grain boundaries (GBs), uncontrolled side reactions at electrode-OCE interfaces, and, equally importantly, defects evolution (e.g., void growth and crack propagation) that leads to local current concentration and mechanical failure inside and on OCEs. Here, taking advantage of a dynamically crosslinked aprotic polymer with non-covalent -CH3⋯CF3 bonds, we developed a plastic ceramic electrolyte (PCE) by hybridizing the polymer framework with ionically conductive ceramics. Using in-situ synchrotron X-ray technique and Cryogenic transmission electron microscopy (Cryo-TEM), we uncover that the PCE exhibits self-healing/repairing capability through a two-step dynamic defects removal mechanism. This significantly suppresses the generation of hotspots for Li0 penetration and chemomechanical degradations, resulting in durability beyond 2000 hours in Li0-Li0 cells at 1 mA/cm2. Furthermore, by introducing a polyacrylate buffer layer between PCE and Li0-anode, long cycle life >3600 cycles was achieved when paired with a 4.2 V zero-strain cathode, all under near-zero stack pressure.

Fabrication and X-ray microtomography of sandwich-structured PEEK implants for skull defect repair

Bone defects pose a significant risk to human health. Medical polyetheretherketone (PEEK) is an excellent implant material for bone defect repair, but it faces the challenge of bone osteoconduction and osseointegration. Osteoconduction describes the process by which bone grows on the surface of the implant, while osseointegration is the stable anchoring of the implant achieved by direct contact between the bone and the implant. Bone defects repair depends on the implant’s three-dimensional spatial structure, including pore size, porosity, and interconnections to a great extent. However, it is challenging to fabricate the porous structures to meet specific requirements and to characterize them without causing damage. In this study, we designed and fabricated sandwich-like PEEK implants mimicking the three-layer structures of the skull, whose defects imposes a significant burden on young adulthood and paediatric populations, and performed in-line phase-contrast synchrotron X-ray microtomography to non-destructively investigate the internal porous microstructures. The sandwich-like three-layer microstructure, comprising a dense layer, a loose layer and a dense layer in succession, exhibits structural similarity to that in a natural skull. This work demonstrated the fabrication of the sandwich-like PEEK implant that could potentially enhance osteoconduction and osseointegration. Furthermore, the interior structures and residual porogen sodium chloride particles were observed within the PEEK implant, which cannot be realized by other microscopic methods without destroying the sample. It highlights the advantages and potential of using synchrotron X-ray microtomography to analyze the structure of biomedical materials. This study provides theoretical guidance for the further design and fabrication of PEEK bone repair materials and will advance the clinical application of innovative bioactive bone repair materials.

Domain switching and shear-mode piezoelectric response induced by cross-poling in polycrystalline ferroelectrics

The mechanisms contributing to the electromechanical response of piezoelectric ceramics in the shear mode have been investigated using high-energy synchrotron x-ray diffraction. Soft lead zirconate titanate ceramic specimens were subjected to an electric field in the range 0.2–3.0 MV m−1, perpendicular to that of the initial poling direction, while XRD patterns were recorded in transmission. At low electric field levels, the axial strains remained close to zero, but a significant shear strain occurred due to the reversible shear-mode piezoelectric coefficient. Both the axial and shear strains increased substantially at higher field levels due to irreversible ferroelectric domain switching. Eventually, the shear strain decreased again as the average remanent polarization became oriented toward the electric field direction. The lattice strain and domain orientation distributions follow the form of the total strain tensor, enabling the domain switching processes to be monitored by the rotation of the principal strain axis. Reorientation of this axis toward the electric field direction occurred progressively above 0.6 MV m−1, while the angle of rotation increased from 0° to approximately 80° at the maximum field of 3.0 MV m−1. A strong correlation was established between the effective strains associated with different crystallographic directions, which was attributed to the effects of elastic coupling between grains in the polycrystal.

Sub-millisecond keyhole pore detection in laser powder bed fusion using sound and light sensors and machine learning

Abstract Laser powder bed fusion is a mainstream additive manufacturing technology widely used to manufacture complex parts in prominent sectors, including aerospace, biomedical, and automotive industries. However, during the printing process, the presence of an unstable vapor depression can lead to a type of defect called keyhole porosity, which is detrimental to the part quality. In this study, we developed an effective approach to locally detect the generation of keyhole pores during the printing process by leveraging machine learning and a suite of optical and acoustic sensors. Simultaneous synchrotron x-ray imaging allows the direct visualization of pore generation events inside the sample, offering high-fidelity ground truth. A neural network model adopting SqueezeNet architecture using single-sensor data was developed to evaluate the fidelity of each sensor for capturing keyhole pore generation events. Our comparative study shows that the near infrared images gave the highest prediction accuracy, followed by 100kHz and 20kHz microphones, and the photodiode sensitive to processing laser wavelength had the lowest accuracy. Using a single sensor, over 90% prediction accuracy can be achieved with a temporal resolution as short as 0.1 ms. A data fusion scheme was also developed with features extracted using SqueezeNet neural network architecture and classification using different machine learning algorithms. Our work demonstrates the correlation between the characteristic optical and acoustic emissions and the keyhole oscillation behavior, and thereby provides strong physics support for the machine learning approach.

Polymeric Ionic Liquid-Enabled In Situ Protection of Li Anodes for High-Performance Li-O2 Batteries.

Redox mediators (RMs) have shown promise in enhancing Li-O2 battery cycling stability by reducing overpotential. However, their application is hindered by the shuttle effect, leading to RM loss and Li anode corrosion. Here, we introduce a polyionic liquid, poly (1-Butyl-3-vinylimidazolium bis(trifluoromethanesulfonylimine)) ([PBVIm]- TFSI) as an additive, showcasing a novel Li anode protection strategy for LiI-mediated Li-O2 batteries. [PBVIm]+ cations migrate to the Li anode, forming a protective cationic shield that promotes uniform Li+ deposition. The addition of [PBVIm]-TFSI enhances the cycling stability, achieving 105 cycles at 200 mA·g-1, compared to the cell with LiI which exhibited 38 cycles under the same conditions. Synchrotron X-ray tomography reveals the evolution of this protective layer, providing insights into its formation mechanism, in conjunction with XPS analysis. Our findings offer a new approach to Li anode protection in Li-O2 batteries, emphasizing the critical role of interfacial engineering for battery performance.

Damage mechanisms of a metastable β-titanium alloy with bimodal microstructure revealed by void growth models using synchrotron X-ray microtomography

Damage mechanisms of a metastable β-titanium alloy with bimodal microstructure revealed by void growth models using synchrotron X-ray microtomography

Solid-State Phase Transformation Kinetics and Mechanisms in Additively Manufactured Ti–6Al–4V Studied Using In-Situ High-Energy Synchrotron X-ray Diffraction

Solid-State Phase Transformation Kinetics and Mechanisms in Additively Manufactured Ti–6Al–4V Studied Using In-Situ High-Energy Synchrotron X-ray Diffraction

On the Origin of Capacity Increase in Rechargeable Magnesium Batteries with Manganese Oxide Cathodes and Copper Metal Current Collectors.

Rechargeable magnesium batteries (RMBs), with Cu as positive electrode current collector (CC), typically display a gradual capacity increase with cycling. Whereas the origin of this was suggested in gradual active material electro-activation, the fact that this is prevalent in many positive electrode material systems remains unexplained. Herein, we elucidate the underlying mechanism through a series of multiscale joint operando X-ray characterizations, including operando synchrotron X-ray diffraction and imaging technology. We select a series of manganese oxides as benchmark positive electrodes and find that no magnesium ions are stored within the lattices of these materials, despite an apparent cell capacity increase with cycling. The origin of capacity increase is rooted in the gradual electrochemical corrosion of metallic Cu, release of Cu(I, II) species in electrolyte, and their subsequent redox activity, resulting in apparent electrode capacity gains. Furthermore, the shuttle and redox speciation of Cu ions trigger the irreversible depletion of both the Cu CC (or any other source) and the magnesium metal, ultimately leading to cell failure. Our work suggests the need to reconsider the appropriateness of using Cu as a positive electrode CC for RMBs.

Interdependence of Support Wettability - Electrodeposition Rate- Sodium Metal Anode and SEI Microstructure.

This study examines how current collector support chemistry (sodiophilic intermetallic Na2Te vs. sodiophobic baseline Cu) and electrodeposition rate affect microstructure of sodium metal and its solid electrolyte interphase (SEI). Capacity and current (6 mAh cm-2, 0.5-3 mA cm-2) representative of commercially relevant mass loading in anode-free sodium metal battery (AF-SMBs) are analyzed. Synchrotron X-ray nanotomography and grazing-incidence wide-angle X-ray scattering (GIWAXS) are combined with cryogenic ion beam (cryo-FIB) microscopy. Highlighted are major differences in film morphology, internal porosity, and crystallographic preferred orientation e.g. (110) vs. (100) and (211) with support and deposition rate. Within the SEI, sodium fluoride (NaF) is more prevalent with Te-Cu versus sodium hydride (NaH) and sodium hydroxide (NaOH) with baseline Cu. Due to competitive grain growth the preferred orientation of sodium crystallites depends on film thickness. Mesoscale modeling delineates the role of SEI (ionic conductivity, morphology) on electrodeposit growth and onset of electrochemical instability.

Morphological, molecular and 3D synchrotron X-ray tomographic characterizations of Helicascus satunensis sp. nov., a novel mangrove fungus.

A new species of Helicascus satunensis sp. nov. was collected on mature dead fruits of the Nypa palm in Satun Province, southern Thailand. Its morphological characteristics are similar to those of the genus Helicascus. Recently, a genus Helicascus with three species from marine habitats worldwide was studied. The morphology of this fungus was investigated and combined with multigene sequence analyzes of small subunit (SSU), large subunit (LSU), internal transcribed spacer (ITS) ribosomal DNA, translation elongation factor 1-alpha (TEF-1α) and RNA polymerase II (RPB2) genes. Morphologically, H. satunensis sp. nov. is characterized by semi-immersed, lenticular ascomata, multilocules, a bitunicate ascus and smooth, obovoid, dark brown ascospores that are one-septate and unequally two-celled. In addition, 3D visualization using synchrotron X-ray tomography was performed to investigate the interaction between fruiting body and substrata. Molecular phylogeny with multigene revealed that H. satunensis sp. nov. belongs to the family Morosphaeriaceae, order Pleosporales, class Dothideomycetes. Furthermore, H. satunensis sp. nov. forms a well-supported clade with Helicascus species described from marine habitats. Based on the unique morphological and molecular evidence, we propose this fungus, H. satunensis sp. nov., as a new species for Helicascus.

Unconventional Hexagonal Close-Packed High-Entropy Alloy Surfaces Synergistically Accelerate Alkaline Hydrogen Evolution.

Accelerating the alkaline hydrogen evolution reaction (HER), which involves the slow cleavage of HO-H bonds and the adsorption/desorption of hydrogen (H*) and hydroxyl (OH*) intermediates, requires developing catalysts with optimal binding strengths for these intermediates. Here, the unconventional hexagonal close-packed (HCP) high-entropy alloy (HEA) atomic layers are prepared composed of five platinum-group metals to enhance the alkaline HER synergistically. The breakthrough is made by layer-by-layer heteroepitaxial deposition of subnanometer RuRhPdPtIr HEA layers on the HCP Ru seeds, despite the thermodynamic stability of Rh, Pd, Pt, and Ir in a face-centered cubic (FCC) structure except for Ru. The synchrotron X-ray absorption spectroscopy (XAS) confirms the atomic mixing and coordination environment of HCP RuRhPdPtIr HEA. Most importantly, they exhibit notable improvements in both electrocatalytic activity and durability for the HER in an alkaline environment, as compared to their FCC RuRhPdPtIr counterparts. Electrochemical measurements, operando XAS analysis, and density functional theory unveil that the binding strengths of H* and OH* intermediates on the active Pt and Ir sites can be weakened and strengthened to a moderate level, respectively, by mixing non-active Ru, Rh, and Pd atoms with Pt and Ir atoms within the HCP HEA with strong synergistic electronic effects.

Superconducting properties and electronic structure of CuAl2-type transition-metal zirconide Fe1-xNixZr2

CuAl2-type transition-metal (Tr) zirconides are a superconductor family, and the Tr-site element substitution largely modifies its transition temperature (Tc). Here, we synthesized polycrystalline samples of Fe1-xNixZr2 by arc melting. The crystal structure and the superconducting properties were studied through synchrotron X-ray diffraction, magnetic susceptibility, electrical resistivity, and specific heat measurements. Bulk superconductivity was observed for 0.4 ≤ x ≤ 0.8, and the highest Tc of 2.8 K was observed for x = 0.6. The obtained superconductivity phase diagram exhibits a dome-shaped trend, which is similar to unconventional superconductors, where magnetic fluctuations are essential for superconductivity. In addition, from the c/a lattice constant ratio analysis, we show the possible relationship between the suppression of bulk superconductivity in the Ni-rich compositions and a collapsed tetragonal transition.

Visualizing the Structure and Dynamics of Transition Metal-Based Electrocatalysts Using Synchrotron X-Ray Absorption Spectroscopy.

As the global energy structure evolves and clean energy technologies advance, electrocatalysis has become a focal point as a critical conversion pathway in the new energy sector. Transitional metal electrocatalysts (TMEs) with their distinctive electronic structures and redox properties show great potential in electrocatalytic reactions. However, complex reaction mechanisms and kinetic limitations hinder the improvement of energy conversion efficiency, highlighting the necessity for comprehensive studies on structure and performance of electrocatalysts. X-ray Absorption Fine Structure (XAFS) spectra stand out as a robust tool for examining the electrocatalyst's structures and performance due to its atomic selectivity and sensitivity to local environments. This review delves into the application of XAFS technology in characterizing TMEs, providing in-depth analyses of X-ray Absorption Near-Edge Structure (XANES) spectra, and Extended XAFS (EXAFS) spectra in both R-space and k-space. These analyses reveal intrinsic structural information, electronic interactions, catalyst stability, and aggregation morphology. Furthermore, the paper examines advancements in in-situ XAFS techniques for real-time monitoring of active site changes, capturing critical intermediate and transitional states, and elucidating the evolution of active species during electrocatalytic reactions. These insights deepen our understanding on structure-activity relationship of electrocatalysts and offer valuable guidance for designing and developing highly active and stable electrocatalysts.

Influence of grain size on strain-induced phase transformation in a CrCoNi multi-principal element alloy

A Cr40Co40Ni20 (at.%) alloy with different grain/crystallite sizes was analyzed through in-situ synchrotron X-ray diffraction during tensile testing. The FCC starting structure underwent a partial strain-induced transformation to HCP (TRIP effect) and the percent transformed was measured throughout the deformation. The critical stress required to form a certain HCP fraction was shown to follow a Hall-Petch relation (σTRIP = σTRIP,0+ kTRIPd-0.5), with the Hall-Petch slope being approximately the same for yield stress and TRIP effect (ky ≈ kTRIP). Furthermore, this work developed a Hall-Petch-based model that correlates the applied stress, the transformed phase fraction, and the initial FCC grain/crystallite size. It predicts the stress required to form a certain HCP fraction, or the fraction formed when a certain stress is applied, for different grain/crystallite sizes. We also proposed a mechanism to explain the grain/crystallite size dependence of the TRIP effect and discuss how the TRIP effect and its early activation in the Cr40Co40Ni20 alloy provide high work-hardening capacity, which improves ductility and toughness. Here, a refined FCC grain size (d = 1.3; c = 0.7 μm) was shown to increase the yield stress by at least 100 % (417 → 834 MPa), compared to a coarser grain material (17; 6.8 μm), while maintaining a high ductility of 41 %. This work contributes to a better understanding of the deformation mechanisms, mainly the strain-induced phase transformation (TRIP), highlighting their impact and importance on mechanical properties.

Temperature and Pressure Effects on Phase Transitions and Structural Stability in CsPb2Br5 and CsPb2Br4I Perovskite-Derived Halides.

All-inorganic perovskites exhibit outstanding light absorption properties in the visible range suitable for solar energy applications. We focus on the synthesis of CsPb2(Br,I)5 using mechanochemical procedures. Synchrotron X-ray diffraction (SXRD) data are essential for determining the crystallographic evolution in the 295-753 K temperature range. From room temperature to 573 K, the crystal structure is refined in a two-dimensional (2D) tetragonal framework (space group: I4/mcm) consisting of layers of face sharing [Pb(Br,I)8] polyhedra. Above a transition temperature of Tt = 630 and 621 K, identified from differential scanning calorimetry (DSC) curves for CsPb2Br5 and CsPb2Br4I, respectively, a cubic three-dimensional (3D) corner-sharing perovskite structure is identified, showing substantial Cs and (Br,I) deficiency. A more ionic character for Cs-halide versus Pb-halide is derived from the evolution of the anisotropic atomic displacements. An ultralow thermal conductivity of 0.35-0.18 W m-1 K-1 is related to the low Debye temperatures. From high-pressure SXRD studies, the change in B0 can be attributed to a basic expansion of the unit-cell volume caused by the chemical pressure from iodine within the CsPb2Br5 framework. UV-vis-NIR spectroscopy revealed optical gaps of approximately 2.93 and 2.50 eV, respectively, which agrees with ab initio calculations.

Pressure-induced superconductivity and phase transition in PbSe and PbTe

Abstract The IV-VI semiconducting chalcogenides are a large material family with distinct physical behavior. Here, we systematically investigate the effect of pressure on the electronic and crystal structure in PbSe and PbTe by combining high-pressure electrical transport and synchrotron x-ray diffraction (XRD) measurements. The resistivity of PbSe and PbTe changes dramatically under high pressure and a non-monotonic evolution of ρ(T) is observed. Both PbSe and PbTe are found to undergo semiconductor-metal transition upon compression and show superconductivity under higher pressure. The structural evolutions from the Fm-3m to Pnma phase and then to the Pm-3m phase in PbSe are verified by the x-ray diffraction. The present findings reveal the internal correlation between the structural evolution and the physical properties in lead chalcogenides.

Tailoring Atomic Ordering Uniformity Enables Selectively Leached Nanoporous Pd-Ni-P Metallic Glass for Enhanced Glucose Sensing.

Constructing nanostructures, such as nanopores, within metallic glasses (MGs) holds great promise for further unlocking their electrochemical capabilities. However, the MGs typically exhibit intrinsic atomic-scale isotropy, posing a significant challenge in directly fabricating anisotropic nanostructures using conventional chemical synthesis. Herein a selective leaching approach, which focuses on tailoring the uniformity of atomic ordering, is introduced to achieve pore-engineered Pd-Ni-P MG. This innovative approach significantly boosts the number of exposed active sites, thereby enhancing the electrochemical sensitivity for glucose detection. Electrochemical tests reveal that the nanoporous Pd-Ni-P MG exhibits high sensitivity (3.19mA mm⁻¹ cm⁻2) and remarkable stability (97.7% current retention after 1000 cycles). During electrochemical cycling, synchrotron X-ray pair distribution function and X-ray absorption fine structure analyses reveal that the distance between active sites decreases, enhancing electron transport efficiency, while the medium-range ordered structure of the Pd-Ni-P MG remains stable, contributing to its exceptional glucose sensing capabilities. A microglucose sensor is successfully developed by integrating the nanoporous Pd-Ni-P MG with a screen-printed electrode, demonstrating the practical applicability. This study not only offers a new avenue for the design of highly active nanoporous MGs but also sheds light on the mechanisms behind the high electrochemistry performance of MGs.