Neutron Diffraction Research Articles

Neutron diffraction from a microgravity-grown crystal reveals the active site hydrogens of the internal aldimine form of tryptophan synthase

Pyridoxal 5'-phosphate (PLP), the biologically active form of vitamin B6, is an essential cofactor in many biosynthetic pathways. The emergence of PLP-dependent enzymes as drug targets and biocatalysts, such as tryptophan synthase (TS), has underlined the demand to understand PLP-dependent catalysis and reaction specificity. The ability of neutron diffraction to resolve the positions of hydrogen atoms makes it an ideal technique to understand how the electrostatic environment and selective protonation of PLP regulates PLP-dependent activities. Facilitated by microgravity crystallization of TS with the Toledo Crystallization Box, we report the 2.1 Å joint X-ray/neutron (XN) structure of TS with PLP in the internal aldimine form. Positions of hydrogens were directly determined in both the α- and β-active sites, including PLP cofactor. The joint XN structure thus provides insight into the selective protonation of the internal aldimine and the electrostatic environment of TS necessary to understand the overall catalytic mechanism.

Order–Disorder Phase Transitions in Fe81Ga19–RE Alloys (RE = Dy, Er, Tb, Yb) According to Neutron Diffraction Data

Order–Disorder Phase Transitions in Fe81Ga19–RE Alloys (RE = Dy, Er, Tb, Yb) According to Neutron Diffraction Data

The systematic structural studies of some Byzantine ceramic fragments from Dobrudja region of Romania: Raman spectroscopy, neutron diffraction, and imaging data

AbstractThe systematic studies of composition and spatial distribution of main phases inside volume of 25 fragments of Byzantine ceramic obtained in archeological works in the Dobrudja region, Romania, have been performed using neutron diffraction and tomography, and Raman spectroscopy. The obtained structural data on the content of phases, the presence of calcite grains and pores, and the uniformity of phase spatial distribution made it possible to systematize the studied fragments and correlate them with clay sources or pottery workshop. The experimental possibilities of neutron methods of nondestructive structural diagnostics as well as the structural markers provided by them in the studies of ceramic samples are discussed.

Martensitic Transformation Behavior of Fe–Ni–C Alloys Monitored by <i>In-situ</i> Neutron Diffraction during Cryogenic Cooling

Martensitic Transformation Behavior of Fe–Ni–C Alloys Monitored by <i>In-situ</i> Neutron Diffraction during Cryogenic Cooling

A fast ceramic mixed OH−/H+ ionic conductor for low temperature fuel cells

Low temperature ionic conducting materials such as OH− and H+ ionic conductors are important electrolytes for electrochemical devices. Here we show the discovery of mixed OH−/H+ conduction in ceramic materials. SrZr0.8Y0.2O3-δ exhibits a high ionic conductivity of approximately 0.01 S cm−1 at 90 °C in both water and wet air, which has been demonstrated by direct ammonia fuel cells. Neutron diffraction confirms the presence of OD bonds in the lattice of deuterated SrZr0.8Y0.2O3-δ. The OH− ionic conduction of CaZr0.8Y0.2O3-δ in water was demonstrated by electrolysis of both H218O and D2O. The ionic conductivity of CaZr0.8Y0.2O3-δ in 6 M KOH solution is around 0.1 S cm−1 at 90 °C, 100 times higher than that in pure water, indicating increased OH− ionic conductivity with a higher concentration of feed OH− ions. Density functional theory calculations suggest the diffusion of OH− ions relies on oxygen vacancies and temporarily formed hydrogen bonds. This opens a window to discovering new ceramic ionic conducting materials for near ambient temperature fuel cells, electrolysers and other electrochemical devices.

Evolution of the Cell Structure, Ionic Conductivity, and Elastic Modulus of the γ-Irradiated LLZTO Electrolyte via Neutron Diffraction and Nanoindentation

Evolution of the Cell Structure, Ionic Conductivity, and Elastic Modulus of the γ-Irradiated LLZTO Electrolyte via Neutron Diffraction and Nanoindentation

The use of diffraction techniques for understanding structure–property relationships in Heusler alloys

Heusler compounds are intermetallic alloys that are capable of a wide range of unique properties such as magnetocaloric, thermoelectric, and magnetic-shape-memory effects, antiferromagnetism, superconductivity, and they can even act as topological insulators. These multifunctional behaviors make Heusler alloys prime candidates for numerous smart device applications. However, their specific properties critically depend on their crystalline structures, chemical order, structural phase transformations, and crystallographic texture. Thus, as compositions and processing parameters are varied it becomes essential to be able to accurately characterize the structure of these materials at various scales. This paper provides a brief review of diffraction-based characterization techniques ideally suited for the characterization of Heusler alloys with examples from our previous works including use of synchrotron, neutron, and electron diffraction, especially as a function of temperature and/or magnetic field to explain important phenomena demonstrated by Heusler alloys.

Microstructural and mechanical behavior of second-phase hardened porous refractory Ti-Nb-Zr-Ta alloys

Second-phase hardening in refractory high-entropy alloys (RHEAs) has been recognized as one of the main routes to significantly improve their mechanical properties. However, their costbenefit should not be compromised. Thus, we designed second-phase strengthened RHEAs by a low-cost powder metallurgy method. We induced the formation of FCC (face-centered cubic) ZrC second phase, which has not been reported in Ti-Nb-Zr-Ta alloys before and may be easily confused with the FCC-Zr due to the complexity of identifying carbon by conventional methods. We used neutron diffraction and electron backscatter diffraction for microstructural studies, as well as hardness, ultrasonic and compression techniques for assessing mechanical properties. Our investigation centered on equiatomic and equimassic Ti-Nb-Zr-Ta alloys, both displaying similar grain morphology and porosity but differing in grain sizes and phases. The variation in grain size was attributed to the influence of Ta as a grain growth pinning element. Our second-phase ZrC hardened alloys revealed higher stiffness and hardness, surpassing those documented in the existing literature.

Multi-scale investigation of microstructure and texture evolution during equal channel angular pressing of silver

A multi-scale investigation was carried out on pure silver subjected to equal channel angular pressing up to 3 passes. Microstructure and texture were examined using scanning and transmission electron microscopy as well as diffraction of neutron and high-energy synchrotron radiation. The evolution of the deformation substructure in the material is in accordance with its low stacking fault energy followed by restoration mechanisms leading to overall microstructural refinement. The restoration mechanism sets in as early as after 3 passes. Twinning involved in the deformation process supports grain refinement through mechanisms of dynamic recrystallization involving strain-induced boundary migration contributing to a steady-state grain size. The global texture, as measured by neutron diffraction, forms through a twin-assisted deformation mechanism. The texture is found heterogeneous through thickness.Graphical abstract

Principal Preferred Orientation Evaluation of Steel Materials Using Time-of-Flight Neutron Diffraction

Comprehensive information on in situ microstructural and crystallographic changes during the preparation/manufacturing processes of various materials is highly necessary to precisely control the microstructural morphology and the preferred orientation (or texture) characteristics for achieving an excellent strength–ductility–toughness balance in advanced engineering materials. In this study, in situ isothermal annealing experiments with cold-rolled 17Ni-0.2C (mass%) martensitic steel sheets were carried out by using the TAKUMI and ENGIN-X time-of-flight neutron diffractometers. The inverse pole figures based on full-profile refinement were extracted to roughly evaluate the preferred orientation features along three principal sample directions of the investigated steel sheets, using the General Structure Analysis System (GSAS) software with built-in generalized spherical harmonic functions. The consistent rolling direction (RD) inverse pole figures from TAKUMI and ENGIN-X confirmed that the time-of-flight neutron diffraction has high repeatability and statistical reliability, revealing that the principal preferred orientation evaluation of steel materials can be realized through 90° TD ➜ ND (transverse direction ➜ normal direction) rotation of the investigated specimen on the sample stage during two neutron diffraction experiments. Moreover, these RD, TD, and ND inverse pole figures before and after the in situ experiments were compared with the corresponding inverse pole figures recalculated from the MUSASI-L complete pole figure measurement and the HIPPO in situ microstructure evaluation, respectively. The similar orientation distribution characteristics suggested that the principal preferred orientation evaluation method can be applied to the in situ microstructural evolution of bulk orthorhombic materials and spatially resolved principal preferred orientation mappings of large engineering structure parts.

Recrystallization of bulk nanostructured magnesium alloy AZ31 after severe plastic deformation: an in situ diffraction study

The magnesium alloy AZ31, which has undergone high-pressure torsion processing, was subjected to in situ annealing microbeam synchrotron high-energy X-ray diffraction and compared to the as-received rolled sheet material that was investigated through in situ neutron diffraction. While the latter only exhibits thermal expansion and minor recovery, the nanostructured specimen displays a complex evolution, including recovery, strong recrystallization, phase transformations, and various regimes of grain growth. Nanometer-scale grain sizes, determined using Williamson–Hall analysis, exhibit seamless growth, aligning with the transition to larger grains, as assessed through the occupancy of single-grain reflections on the diffraction rings. The study uncovers strain anomalies resulting from thermal expansion, segregation of Al atoms, and the kinetics of vacancy creation and annihilation. Notably, a substantial number of excess vacancies were generated through high-pressure torsion and maintained for driving the recrystallization and forming highly activated volumes for diffusion and phase precipitation during heating. The unsystematic scatter observed in the Williamson–Hall plot indicates high dislocation densities following severe plastic deformation, which significantly decrease during recrystallization. Subsequently, dislocations reappear during grain growth, likely in response to torque gradients in larger grains. It is worth noting that the characteristics of unsystematic scatter differ for dislocations created at high and low temperatures, underscoring the strong temperature dependence of slip system activation.Graphical

Experimental investigation and thermodynamic assessment of the BaCl2–CeCl3 system

The thermodynamic and thermo-physical properties of the molten salt system ▪ have been investigated using an experimental and modelling approach. This molten salt system includes a single intermediate compound ▪, whose structure has been investigated using X-ray and neutron diffraction. Furthermore, this system exhibits solubility of ▪ in ▪ at high temperatures up to a concentration of around 25% ▪ at 1060 K. Additionally, our measurements show solubility of ▪ in ▪ up to about 5% ▪ at 973 K. The investigation of these solid solutions has been performed using quenching experiments and subsequent post-characterisation by X-ray diffraction (XRD). Phase diagram equilibria have also been investigated using differential scanning calorimetry (DSC). Using the aforementioned information on phase transitions, intermediate compound formation, and mutual solid solubility, a thermodynamic assessment of the system has been performed using the CALPHAD method. The model for the Gibbs energy of the liquid solution is the quasi-chemical formalism in the quadruplet approximation, while the model for the Gibbs energy of the solid solutions is a two-sublattice polynomial model.

Weyl metallic state induced by helical magnetic order

In the rapidly expanding field of topological materials there is growing interest in systems whose topological electronic band features can be induced or controlled by magnetism. Magnetic Weyl semimetals, which contain linear band crossings near the Fermi level, are of particular interest owing to their exotic charge and spin transport properties. Up to now, the majority of magnetic Weyl semimetals have been realized in ferro- or ferrimagnetically ordered compounds, but a disadvantage of these materials for practical use is their stray magnetic field which limits the minimum size of devices. Here we show that Weyl nodes can be induced by a helical spin configuration, in which the magnetization is fully compensated. Using a combination of neutron diffraction and resonant elastic x-ray scattering, we find that below TN = 14.5 K the Eu spins in EuCuAs develop a planar helical structure which induces two quadratic Weyl nodes with Chern numbers C = ±2 at the A point in the Brillouin zone.

Magnetic Helicity in a Chiral‐Polar Magnet Ni2InSbO6

The class of chiral‐polar magnets has recently captured significant interest in scientific study due to their intriguing physical phenomena. Among all the chiral‐polar magnets, Ni2InSbO6 stands out because of its unique attributes, such as the emergence of the topological chiral soliton lattice in the presence of an external magnetic field perpendicular to the chiral‐polar axis. However, the magnetic structure of Ni2InSbO6 at zero field has not been well understood yet. This work presents an analysis including polarized optical microscopy and polarized neutron diffraction on a carefully chosen Ni2InSbO6 crystal. Results confirm the predominance of a single chiral‐polar domain within the crystal and indicate the likelihood of cycloidal magnetic ordering under zero magnetic field, alongside the observation of net magnetic helicity. The existence of both a dominant chiral‐polar domain and a dominant cycloidal magnetic domain within Ni2InSbO6 provides an excellent platform for further exploration of its unconventional physical attributes.

Local structure of concentrated NaFSA solutions in propylene carbonate studied by X-ray and neutron diffraction methods

Abstract The microscopic structure of 10 mol% NaFSA [FSA: bis(fluorosulfonyl)amide]-propylene carbonate (PC) solution has been investigated by means of X-ray and neutron diffraction techniques. The solvation structure of Na+ has been determined from least-squares fitting analysis of X-ray intermolecular difference interference terms observed for 10 mol% NaFSA-PC solution and pure liquid PC. In the present solution, onaverage, 6(1) PC molecules are involved in the first solvation shell of Na+ with intermolecular distance rNaO = 2.26(7) Å, and bond angle ∠Na+…O = C = 169(9)°. Intermolecular correlation between neighboring PC molecules in the solution has been derived from simultaneous least-squares fitting analysis of observed H–H, H–X, and X–X (X: atoms except for H) intermolecular partial structure factors determined from neutron diffraction data for H/D isotopically-substituted sample solutions. An indication of anti-parallel configuration of the nearest neighbor PC molecules has been suggested.

Solid-state and sol-gel synthesis of neodymium molybdate Nd5Mo3O16+δ and study of their crystal structure in the temperature range of 300–700 K by the neutron diffraction

The solid-state and sol-gel synthesis of Nd5Mo3O16+δ neodymium molybdate has been investigated. The sequence of chemical transformations was studied using differential thermal analysis, X-ray diffraction analysis, and infrared spectroscopy. It has been demonstrated that the solid-state synthesis occurs stepwise through the formation of Nd2(MoO4)3 and phases with monoclinic structures. The using of the sol-gel method allows obtaining a single-phase neodymium molybdate directly after decomposition of the organic precursor and decreasing of the synthesis temperature by 200 K. The investigation of the crystal structure was carried out by high resolution neutron diffraction, which revealed non-uniform changes in the neodymium-oxygen interatomic distances with increasing temperature.

Diffusive and displacive phase transitions in Fe-Ga alloys

Phase transitions between structurally ordered phases in Fe–Ga alloys have been studied upon their heating to 850 °C and subsequent cooling to room temperature by neutron diffraction in real-time mode. The transitions between four types of phases have been analyzed: D03 → L12 (both cubic phases), L12 ↔ D019 (cubic – hexagonal), D019 ↔ A2 (hexagonal – cubic). It has been established that all phase transitions include stage of the formation of a disordered state and have a combined, diffusive-displacive nature. The diffusion stages are necessary for the disordering and ordering of the structure, the displacive stage provides a change in the type of the crystal lattice. It can be concluded that the formation of an intermediate disordered state followed by a transition to the final equilibrium state is less energy-consuming than the direct transition to the final state. During the observed transformations, no traces of predicted intermediate structurally ordered tetragonal phases were found. These results may provide new insight into the microscopic basis for the formation of enhanced magnetostriction in Fe–Ga alloys.

Magnetocaloric properties of Mn5(Si,P)B2 compounds for energy harvesting applications

The magnetocaloric properties of Mn5Si1-xPxB2 (0 ≤ x ≤ 1) compounds were studied for energy harvesting applications. The crystal structure and the magnetic structure were characterized by powder X-Ray Diffraction and powder Neutron Diffraction. The results indicate that these magnetocaloric materials crystallize in the tetragonal Cr5B3-type crystal structure. The introduction of P causes a stretching of the c axis and compression of the a-b plane, leading to a decrease in the unit-cell volume V. In the ferromagnetic state the magnetic moments align within the a-b plane, and the magnetic moment of the Mn1 atom on the 16 l site is larger than that of the Mn2 atom on the 4c site. The Curie temperature TC can be adjusted continuously from 305 K (x = 1) to 406 K (x = 0) by replacing Si with P. The corresponding magnetic entropy change varies from 1.90 Jkg−1K−1 (x = 0) to 1.35 Jkg−1K−1 (x = 1) for a magnetic field change of 1 T. The PM-FM transition in these compounds corresponds to a second-order phase transition. Mn5Si1-xPxB2 compounds exhibit a magnetization difference of 28.1 - 31.3 Am2kg−1 for a temperature span of 30 K around TC in an applied magnetic field of 1 T. The considerable change in magnetization, the tunable TC near and above room temperature and the absence of thermal hysteresis make these compounds promising candidates for magnetocaloric energy harvesting materials.

Science in a cup of coffee: A structural study of a trigonelline aqueous solution

Bioactive trigonelline is one of the important components of coffee, contributing to its characteristic undue bitterness. In this report we looked at the structure of an aqueous solution of trigonelline by means of Neutron Diffraction with Isotopic Substitution (NDIS). This experimental approach has been coupled with a Monte Carlo simulation to get an atom-level description of the solution. The rationale behind the present study is to investigate the solvent-solute and the solute-solute interactions; these have implications relevant also to other bioactive molecules and, in addition, can provide basic information on the extraction efficiency and on the solubility of important molecules in coffee. Results indicate a limited short-ranged involvement of the solute trigonelline with the water solvent and a not negligible clustering of trigonelline molecules. The investigated solution contains both positively charged and zwitterionic trigonelline, along with Cl− and H+, with this latter ion involved in hydronium ion formation. Here it is found that the observed structures are compatible with a Zundel-like cation, thus contributing to the still on-going debate on the presence of either Zundel or Eigen complexes in acidic solution. The role of a Zundel-like cation, along with its interaction with the chloride ion, might be related to the extraction and solubility of important molecules in coffee, in order to define the best water composition resulting in the best coffee.

Full-field eigenstrain reconstruction for the investigation of residual stresses in finite length weldments

The reconstruction of welding residual stresses has been performed based on the assumption of continuous processing conditions, owing to the limitations of reconstruction methods. This assumption prevents the attainment of a comprehensive understanding of mechanical deformations in the entire weld zone. The voxel-based eigenstrain (inherent strain) reconstruction method emerges as an appropriate approach for the full-field reconstruction of residual stresses in finite length weldments without such assumption. The innovative reconstruction capability of this advanced method is presented in this study, aiming to comprehend all components of residual stresses and eigenstrains in finite length weldments with discontinuous processing properties using only a single component of experimental data belonging to a limited portion of the specimen. Numerical experiments were conducted to develop the tools. These tools were validated using a case study employing experimental data obtained through contact profilometry measurements from the surface of discharge machine cutting (minimally disturbing cutting) in a bead-on-plate weldment of Inconel alloy 740H designed for ultra-supercritical power generation. The reconstructed two components of normal residual stresses that do not align with the available experimental data were validated by independent neutron diffraction strain scanning quantifications. Furthermore, the reconstruction of residual stresses in the intact component prior to cutting was carried out using the eigenstrains associated with the post-cut state of the weldment.