Search Results (419)

In this study, we investigate the magnetic properties of the molecular compound [Mn(mal)(H₂O)]ₙ (mal = dianion of malonic acid) by integrating microscopic and macroscopic characterization, combining unpolarized neutron diffraction and magnetometry measurements. Neutron diffraction, though non-commonly applied to molecular compounds, proved essential for fully resolving the magnetic structure, as well as overcoming challenges such as hydrogen-related incoherent scattering and difficulties in accurately locating light atoms. Our neutron data provided critical structural details, including the precise location of hydrogen atoms, especially those associated with crystallization water molecules. By conducting low-temperature measurements below the magnetic ordering temperature, we identified the correct Shubnikov space group (Pc’a2₁’) and established a magnetic model consistent with the observed weak ferromagnetism. Our findings reveal that the compound presents a spin-canted structure with a weak ferromagnetic signal along the b-axis. This signal originates primarily from antisymmetric exchange interactions rather than single-ion anisotropy, consistent with the isotropic nature of the Mn(II) (⁶A₁g) ground state. The combined neutron diffraction and magnetometry results provide a comprehensive understanding of how structural and symmetry factors influence the magnetic properties of malonate-based manganese compounds. Full article

Advanced batteries require advanced characterization techniques, and neutron scattering is one of the most powerful experimental methods available for studying next-generation battery materials. Neutron scattering offers a non-destructive method to probe the complex structural and chemical processes occurring in batteries during operation in truly in situ/in operando measurements with a high sensitivity to battery-relevant elements such as lithium. Neutrons have energies comparable to the energies of excitations in materials and wavelengths comparable to atomic distances in the solid state, thus giving access to study structural and dynamical properties of materials on an atomic scale. In this review, a broad overview of selected neutron scattering techniques is presented to illustrate how neutron scattering can be used to gain invaluable information of solid-state battery materials, with a focus on in situ/in operando methods. These techniques span multiple decades of length and time scales to uncover the complex processes taking place fundamentally on the atomic scale and to determine how these processes impact the macroscale properties and performance of functional battery systems. This review serves the solid-state battery research community by examining how the unique capabilities of neutron scattering can be applied to answer critical and unresolved questions of materials research in this field. A thorough and broad perspective is provided with numerous practical examples showing these techniques in action for battery research. Full article

Magnesium aluminates (MgO)_x(Al₂O₃)_1−x belong to a class of refractory materials with important applications in glass and glass–ceramic technologies. Typically, these materials are fabricated from high-temperature molten phases. However, due to the difficulties in making measurements at very high temperatures, information on liquid-state structure and properties is limited. In this work, we employed the method of aerodynamic levitation with CO₂ laser heating at large scale facilities to study the structure of liquid magnesium aluminates in the system (MgO)_x(Al₂O₃)_1−x, with x = 0.33, 0.5, and 0.75, using X-ray and neutron diffraction. We determined the structure factors and corresponding pair distribution functions, providing detailed information on the short-range structural order in the liquid state. The local structures were similar across the range of compositions studied, with average coordination numbers of ${\overline{n}}_{\mathrm{A}\mathrm{l}}^{\mathrm{O}}\sim 4.5$ and ${\overline{n}}_{\mathrm{M}\mathrm{g}}^{\mathrm{O}}\sim 5.1$ and interatomic distances of $r_{\mathrm{AlO}}=1.76-1.78 \mathrm{\AA }$ and $r_{\mathrm{MgO}}=1.93-1.95 \mathrm{\AA }$. The results are in good agreement with previous molecular dynamics simulations. For the spinel endmember MgAl₂O₄ (x = 0.5), the average Mg-O and Al-O coordination numbers gave rise to conflicting values for the inversion coefficient χ, indicating that the structural formula used to describe the solid-state order-disorder transition is not applicable in the liquid state. Full article

The evolution of the mechanical properties of Zr-2.5Nb pressure tubing during irradiation is dependent on dislocation loop densities that are represented by the broadening of X-ray diffraction lines. Empirical models for the integral breadth of the diffraction peaks as a function of operating conditions have been developed to predict the mechanical properties of CANDU reactor pressure tubes as a function of fast neutron flux, time and temperature. Apart from predicting mechanical property changes based on integral breadth measurements, a new model has been developed to retrospectively deduce abnormal operating temperatures of ex-service pressure from the measured line broadening. The application of integral breadth measurements to assess mechanical properties and temperature variations in pressure tubes is described and discussed in terms of the implications for pressure tube integrity. Full article

The structure of the glassy Ge_xTe_1−x system, with x = 0.17, 0.21, 0.28, 0.30, and 0.45, is studied using the small-angle neutron scattering (SANS) technique. The very-low-momentum-transfer region of the diffractogram exhibits distinct behaviour depending on the germanium content. A similar conclusion is drawn from the analysis of the first diffraction peaks observed at higher angles. This system exhibits three composition regions with distinct behaviours: a first zone of low Ge content (up to about 20–25 at.%), a third zone richer in Ge (from about 30 at.% and above), and a second transitional zone between them. These changes are reflected in the parameters that govern Porod’s region, as well as in the region where the first diffraction peaks appear, corroborating previous observations made using other experimental and simulation techniques. Our study provides experimental evidence that could open up new possibilities for conducting simulations using neutron data. The results presented here show that increasing Ge content leads to a strengthening of the intermediate-range order at the expense of a weakening of the short-range order. Full article

The phase evolution of Li-rich Li-Mn-Ni-(Al)-O cathode materials upon heat treatments in the air at 900 °C was studied by X-ray and neutron powder diffraction. In addition, the structures of Li_1.26Mn_0.61−xAl_x Ni_0.15O₂, x = 0.0, 0.05, and 0.10, were refined from neutron powder diffraction data. For two-phase mixtures containing a monoclinic Li₂MnO₃ type phase M and a rhombohedral LiMn_0.5Ni_0.5O₂ type phase R, the structures, compositions, and phase fractions change with heat treatment time. This is realized by the substitution mechanism 3Ni²⁺ ↔ 2Li⁺ + 1Mn⁴⁺, which enables cation transport between the phases. A whole-powder pattern fitting analysis of size and strain broadening shows that strain broadening dominates. The X-ray domain size increases with heat treatment time and is larger than the sizes of the domains of M and R observed by electron microscopy. For heat-treated samples, the domain size is smaller for R than for M and decreases with increasing Al doping. Full article

The use of neutron reflectors is an effective method for improving the quality of neutron sources and neutron delivery systems. In this work, we further develop the method based on the Bragg scattering of neutrons in crystals with large interplanar distances. We compare samples of differently prepared fluorine intercalated graphites by measuring the total cross section for the interaction of neutrons with the samples, depending on the neutron wavelength. The Brag scattering cross section is expected to be the dominant part of the total cross section in all the cases. The results show that all samples provide high reflection efficiency over the entire range of the so-called “neutron reflectivity gap” and beyond it, and that they also allow for the choosing of the optimal intercalation methods. Full article

The development of advanced volume detectors for neutron time-of-flight diffractometers offers exciting new possibilities. This work takes advantage of these advances by implementing a novel data preprocessing algorithm, exemplified for the first time with data acquired during the operation of a singular mounting unit of the POWTEX detector placed at the POWGEN instrument (SNS, ORNL, Oak Ridge, TN, USA). Our approach exploits the additional depth information provided by the volume detector needed to correlate multiple neutron events to neutron trajectories of similar origin and probability. By comparing the properties of these trajectories with the expected physical behavior, one may first identify, then label, and ultimately remove unwanted events due to phenomena such as secondary scattering within the sample environment. This capability has the potential to significantly improve the quality and information content of data collected with neutron diffractometers. Full article

The impact of manufacturing strategies on the development of residual stresses in Dievar steel is presented. Two fabrication methods were investigated: conventional ingot casting and selective laser melting as an additive manufacturing process. Subsequently, plastic deformation in the form of hot rotary swaging at 900 °C was applied. Residual stresses were measured using neutron diffraction. Microstructural and phase analysis, precipitate characterization, and hardness measurement—carried out to complement the investigation—showed the microstructure improvement by rotary swaging. The study reveals that the manufacturing method has a significant effect on the distribution of residual stresses in the bars. The results showed that conventional ingot casting resulted in low levels of residual stresses (up to ±200 MPa), with an increase in hardness after rotary swaging from 172 HV1 to 613 HV1. SLM-manufactured bars developed tensile hoop and axial residual stresses in the vicinity of the surface and large compressive axial stresses (−600 MPa) in the core due to rapid cooling. The subsequent thermomechanical treatment via rotary swaging effectively reduced both the surface tensile (to approximately +200 MPa) and the core compressive residual stresses (to −300 MPa). Moreover, it resulted in a predominantly hydrostatic stress character and a reduction in von Mises stresses, offering relatively favorable residual stress characteristics and, therefore, a reduction in the risk of material failure. In addition to the significantly improved stress profile, rotary swaging contributed to a fine grain (3–5 µm instead of 10–15 µm for the conventional sample) and increased the hardness of the SLM samples from 560 HV1 to 606 HV1. These insights confirm the utility of rotary swaging as a post-processing technique that not only reduces residual stresses but also improves the microstructural and mechanical properties of additively manufactured components. Full article

Internal state variable models are well suited to predict the effects of an evolving microstructure as a result of metal-based additive manufacturing (MBAM) processes in components with complex features. As advanced manufacturing techniques such as MBAM become increasingly employed, accurate methods for predicting residual stresses are critical for insight into component performance. To this end, the evolving microstructural model of inelasticity (EMMI) is suited to modeling these residual stresses due to its ability to capture the evolution of rate- and temperature-dependent material hardening as a result of the rapid thermal cycling present in MBAM processes. The current effort contrasts the efficacy of using EMMI with an elastic–perfectly plastic (EPP) material model to predict the residual stresses for an Inconel 718 component produced via laser powder bed fusion (L-PBF). Both constitutive models are used within a thermo-mechanical finite element framework and are validated by published neutron diffraction measurements to demonstrate the need for higher-fidelity models to predict residual stresses in complex components. Both EPP and EMMI can qualitatively predict the residual stresses trends induced by the L-PBF local raster scanning effects on the component, but the influence of the temperature-dependent yield and lack of plastic strain hardening allowed EPP to perform similar to EMMI away from free surfaces. EMMI offered the most insight at the free surfaces and around critical component features, but this work also highlights EMMI as a process–property-dependent model that needs be calibrated to specimens produced with a similar reference structure for microstructure evolution effects to be accurately predicted. Full article

Hydrogen is the lightest atom and composes approximately half of the atomic content in macromolecules, yet their location can only be inferred or predicted in most macromolecular structures. This is because hydrogen can rarely be directly observed by the most common structure determination techniques (such as X-ray crystallography and electron cryomicroscopy). However, knowledge of hydrogen atom positions, especially for enzymes, can reveal protonation states of titratable active site residues, hydrogen bonding patterns, and the orientation of water molecules. Though we know they are present, this vital layer of information, which can inform a myriad of biological processes, is frustratingly invisible to us. The good news is that, even at modest resolution, neutron crystallography (NC) can reveal this layer and has emerged this century as a powerful tool to elucidate enzyme catalytic mechanisms. Due to its strong and coherent scattering of neutrons, incorporation of deuterium into the protein crystal amplifies the power of NC. This is especially true when solvation and the specific participation of key water molecules are crucial for catalysis. Neutron data allow the modeling of all three atoms in water molecules and have even revealed previously unobserved and unique species such as hydronium (D₃O⁺) and deuteroxide (OD⁻) ions as well as lone deuterons (D⁺). Herein, we briefly review why neutrons are ideal probes for identifying catalytically important water molecules and these unique water-like species, limitations in interpretation, and four vignettes of enzyme success stories from disparate research groups. One of these groups was that of Dr. Chris G. Dealwis, who died unexpectedly in 2022. As a memorial appreciation of his scientific career, we will also highlight his interest and contributions to the neutron crystallography field. As both the authors were mentored by Chris, we feel we have a unique perspective on his love of molecular structure and admiration for neutrons as a tool to query those structures. Full article

The amorphous materials of the Ti₄₅Zr₃₈Ni₁₇ composition synthesized by mechanical alloying are widely recognized for their ability to store hydrogen with gravimetric densities above 2 wt.%. It is also known that those alloys can form a quasicrystalline state after thermal treatment and their structural and hydrogen sorption properties can be altered by doping with various elements. Therefore, in this paper, the results of the studies on the Ti₄₅Zr₃₈Ni₁₇ system with yttrium substituted for titanium and zirconium are presented. We demonstrate that these alloys are able to absorb hydrogen with a concentration of up to 2.7 wt.% while retaining their amorphous structure and they transform into the unique glassy-quasicrystal phase upon annealing. Furthermore, we demonstrate that the in-situ hydrogenation of those new materials is an effortless procedure in which the decomposition of the alloy can be avoided. Moreover, we prove that, in that process, hydrogen does not bind to any specific component of the alloy, which would otherwise cause the formation of simple hydrides or nanoclusters. Full article

Silicate glasses containing silicon, sodium, phosphorous, and calcium have the ability to promote bone regeneration and biodegrade as new tissue is generated. Recently, it has been suggested that adding SrO can benefit tissue growth and silicate glass dissolution. Motivated by these recent developments, the effect of SrO/CaO–CaO/SrO substitution on the local structure and dynamics of Si-Na-P-Ca-O oxide glasses has been studied in this work. Differential thermal analysis has been performed to determine the thermal stability of the glasses after the addition of strontium. The local structure has been studied by neutron diffraction augmented by Reverse Monte Carlo simulation, and the local dynamics by neutron Compton scattering and Raman spectroscopy. Differential thermal analysis has shown that SrO-containing glasses have lower glass transition, melting, and crystallisation temperatures. Moreover, the addition of the Sr²⁺ ions decreased the thermal stability of the glass structure. The total neutron diffraction augmented by the RMC simulation revealed that Sr played a similar role as Ca in the glass structure when substituted on a molar basis. The bond length and the coordination number distributions of the network modifiers and network formers did not change when SrO (x = 0.125, 0.25) was substituted for CaO (25-x). However, the network connectivity increased in glass with 12.5 mol% CaO due to the increased length of the Si-O-Si interconnected chain. The analysis of Raman spectra revealed that substituting CaO with SrO in the glass structure dramatically enhances the intensity of the high-frequency band of 1110–2000 cm⁻¹. For all glasses under investigation, the changes in the relative intensities of Raman bands and the distributions of the bond lengths and coordination numbers upon the SrO substitution were correlated with the values of the widths of nuclear momentum distributions of Si, Na, P, Ca, O, and Sr. The widths of nuclear momentum distributions were observed to soften compared to the values observed and simulated in their parent metal-oxide crystals. The widths of nuclear momentum distributions, obtained from fitting the experimental data to neutron Compton spectra, were related to the amount of disorder of effective force constants acting on individual atomic species in the glasses. Full article

With growing interest in molten salts as possible nuclear fuel systems, knowledge of thermophysical properties of complex salt mixtures, e.g., NaCl-CeCl₃, NaCl-UCl₃ and NaCl-UCl₄, informs understanding and performance modelling of the zero power salt reactor. Fuel density is a key parameter that is examined in a multiscale approach in this paper. In the zero power reactor ‘core’ (cm level), the relative fuel density is estimated for the fuel pin disposition, as well as a function of their pitch (strong effect). Fuel density of the ‘pellet’ (mm–µm level) is first estimated on a geometrical basis, then through tracking pores and cracks using 2D (SEM) and 3D (laser microscopy, LM) techniques. For the nanoscale level, ‘grains’ analysis is done using X-ray diffraction (XRD), revealing the defects, vacancies and swelled grains. Initially, emphasis is on the near-eutectic composition of salt mixtures of CeCl₃ with NaCl as the carrier salt. Cerium trichloride (CeCl₃) is an inactive surrogate of UCl₃ and PuCl₃. The results were measured for the specific salt mixture (70 mol% NaCl and 30 mol% CeCl₃) in this work, establishing that microscopy and XRD are important techniques for measurement of the physical properties of salts component pellets. This work is of significance, as densities of fuel components affect the power evolution through reactivity and the average neutronic behaviour in zero power salt reactors. Full article

Aluminum matrix composites (AMCs) are designed to enhance the performance of conventional aluminum alloys for engineering applications at both room and elevated temperatures. However, the dynamic phase-specific deformation behavior and load-sharing mechanisms of AMCs at elevated temperatures have not been extensively studied and remain unclear. Here, in situ neutron diffraction experiments are employed to reveal the phase-specific structure evolution of additively manufactured Al6061+TiC composites under compressive loading at 250 °C. It is found that the addition of a small amount of nano-size TiC significantly alters the deformation behavior and increases the strength at 250 °C in comparison to the as-printed Al6061. Unlike the two-stage behavior observed in Al6061, the Al6061+TiC composites exhibit three stages during compression triggered by changes in the interphase stress states. Further analysis of Bragg peak intensity and broadening reveals that the presence of TiC alters the dislocation activity during deformation at 250 °C by influencing dislocation slip planes and promoting dislocation accumulation. These findings provide direct experimental observations of the phase-specific dynamic process in AMCs under deformation at an elevated temperature. The revealed mechanisms provide insights for the future design and optimization of high-performance AMCs. Full article