Neutron Diffraction Research Articles

The effect of productive and quality deposition strategies on residual stress for Directed Energy Deposition (DED) process

In the Directed Energy Deposition (DED) realm, challenges persist concerning process stability and mechanical properties in as-built components. Facts like inconsistent laser head feed rate and accumulated heat during multi-layer deposition result in variations in melt pool energy, causing variant clad widths and heights. Moreover, significant residual stress in as-built DED parts can induce excessive distortions and cracking. To tackle these challenges, offline energy control systems that adjust laser power or feed rate have been implemented to manage melt pool energy and improve productivity. Additionally, an innovative online clad height compensation system has been developed to achieve global height geometry, further boosting productivity. However, the impact of these productive and quality control systems on the mechanical properties of austenitic stainless-steel parts, specifically residual stress, remains unexplored. In this research, residual stress measurements in as-built DED thin wall parts fabricated with energy and/or height control strategies using neutron diffraction have been investigated. The control of three key DED parameters influencing residual stress distribution and magnitude has been identified and discussed. Measurements indicate that neither offline energy control nor online height control adversely affects the quality of the thin wall parts and offline LP-based energy control can reduce residual stress magnitude and its variation. Additionally, the height control results in compressive residual stress with elevated magnitudes. Furthermore, aggressive DED parameters hold the potential for further improvement by pairing with an energy control strategy. This study establishes a foundation for further developing comprehensive control strategies designed to enhance the productivity and quality of DED systems.

Dilution induced magnetic localization in Rb(Co[formula omitted]Ni[formula omitted])2Se2 single crystals

We report experimental studies on a series of Rb(Co1−xNix)2Se2 (0.02 ≤x≤ 0.9) powder and single crystal samples using x-ray diffraction, neutron diffraction, magnetic susceptibility, and electronic transport measurements. All compositions are metallic and adopt the body-centered tetragonal structure with I4/mmm space group. Anisotropic magnetic susceptibilities measured on single crystal samples suggest that Rb(Co1−xNix)2Se2 undergo an evolution from ferromagnetism to antiferromagnetism, and finally to paramagnetism with increasing Ni concentration. Neutron diffraction measurements on the samples with x = 0.1, 0.4, and 0.6 reveal an A-type antiferromagnetic order with moments lying in the ab plane. The moment size changes from 0.69 (x=0.1) to 2.80μB (x=0.6) per Co ions. Our results demonstrate that dilution of the magnetic Co ions by substitution of nonmagnetic Ni ions induces magnetic localization and evolution from itinerant to localized magnetism in Rb(Co1−xNix)2Se2.

Effects of compression on the halogen bonding of iodic acid – a neutron diffraction study

ABSTRACT The response of the crystallographic structure of iodic acid has been determined using neutron diffraction up to 7.2 GPa. We observe no evidence of a direct structural phase transition. However, we do observe evidence of a molecular re-orientation, previously suggested by a high pressure experimental Raman study and computational study. We show how the crystal structure responds to the application of pressure and observe an increased extent of the halogen-bonding interactions.

Disclosing the magnetic ground state of PrBaMn2O6

In this work, we report a neutron diffraction study on a single crystal of the layered PrBaMn2O6 perovskite. This compound undergoes two consecutive magnetic transitions with decreasing temperature. At TC ≈ 309 K, a long-range ferromagnetic ordering is established with the Mn magnetic moments oriented along the c axis. Below TN ≈ 240 K, a spin reorientation gives rise to a sudden decrease of the magnetization and the formation of an antiferromagnetic order. This magnetic transition is also accompanied by an electronic localization caused by a structural phase transition from a high-temperature tetragonal phase (P4/mmm) into a low-temperature orthorhombic one (P21am). Our neutron diffraction study at 12 K has unambiguously identified that the ground magnetic structure for this compound is a layered antiferromagnetic structure along the c axis with the Mn moments oriented in the ab plane along one diagonal of the primitive tetragonal cell. No sign of magnetic scattering associated to a CE-type magnetic structure was found in our study, discarding its occurrence in this compound. This result excludes the occurrence of a charge order transition to account for the electronic localization and it is fully consistent with previous structural studies showing a unique crystallographic site for Mn atom in the low-temperature phase. A symmetry analysis was carried out to identify the magnetic space group of the ferromagnetic order above TN and the two possible groups for the antiferromagnetic ordering below TN.

Estimation of the Coherently Scattering Domain Size in Alloys from Neutron Diffraction Data

Estimation of the Coherently Scattering Domain Size in Alloys from Neutron Diffraction Data

Quantum refinement in real and reciprocal space using the Phenix and ORCA software.

X-ray and neutron crystallography, as well as cryogenic electron microscopy (cryo-EM), are the most common methods to obtain atomic structures of biological macromolecules. A feature they all have in common is that, at typical resolutions, the experimental data need to be supplemented by empirical restraints, ensuring that the final structure is chemically reasonable. The restraints are accurate for amino acids and nucleic acids, but often less accurate for substrates, inhibitors, small-molecule ligands and metal sites, for which experimental data are scarce or empirical potentials are harder to formulate. This can be solved using quantum mechanical calculations for a small but interesting part of the structure. Such an approach, called quantum refinement, has been shown to improve structures locally, allow the determination of the protonation and oxidation states of ligands and metals, and discriminate between different interpretations of the structure. Here, we present a new implementation of quantum refinement interfacing the widely used structure-refinement software Phenix and the freely available quantum mechanical software ORCA. Through application to manganese superoxide dismutase and V- and Fe-nitrogenase, we show that the approach works effectively for X-ray and neutron crystal structures, that old results can be reproduced and structural discrimination can be performed. We discuss how the weight factor between the experimental data and the empirical restraints should be selected and how quantum mechanical quality measures such as strain energies should be calculated. We also present an application of quantum refinement to cryo-EM data for particulate methane monooxygenase and show that this may be the method of choice for metal sites in such structures because no accurate empirical restraints are currently available for metals.

Freezing of short-range ordered antiferromagnetic clusters in the CrFeTi2O7system.

We report on the CrFeTi2O7(CFTO) system using a combination of x-ray diffraction, dc magnetization, ac susceptibility, specific heat and neutron diffraction measurements. CFTO is seen to crystallize in a monoclinic P21/a symmetry. It shows a glassy freezing at Tf ~ 22 K, characterized by the observation of bifurcation between ZFC and FC χ (T) curves, frequency dispersion across Tf in ac susceptibility, and follows Vogel-Fulcher and power law type critical dynamics, very slow relaxation of iso-thermal remanent magnetization with time and the absence of an anomaly in the temperature dependence of specific heat measurements. The microscopic neutron diffraction analysis of CFTO not only confirms the absence of long-range antiferromagnetic ordering but also exhibits diffuse scattering due to the presence of short-range ordered antiferromagnetically correlated spin clusters.&#xD.

Ni4Nb1.8W0.1Ti0.1O9: Stabilization of the I-Type Ni4Nb2O9 Structure and First Magnetic Study of This Corundum-like Compound.

For the first time, we report on the structural and magnetic properties of a polycrystalline sample of Ni4Nb2O9 from I-type (Fdd2), obtained by the partial cosubstitution of Nb5+ by Ti4+ and W6+. The crystal structure is investigated by combining synchrotron X-ray, neutron, and electron diffraction at room temperature. This I-type structure is derived from the corundum-like Ni4Nb2O9 II-type (Pbcn) and is noncentrosymmetric and polar. The Ni-lattice is composed of the stacking of distorted honeycomb layers with double zigzag ribbons 60° disoriented from each other in two successive double layers. The connection between layers is ensured by the sharing of octahedra faces building (Nb,W,Ti)2O9, Ni2O9, and Ni3O12 units. This study shows how the disruption of the Nb2O6 units by smaller d0 cations impacts the structure, significantly modifying the Ni network and, thus, the magnetic properties. The latter were studied by dc- and ac-magnetic susceptibility, and the magnetic structure was solved by neutron powder diffraction. A ferrimagnetic behavior occurs below 68 K, followed by a re-entrant spin-glass-like behavior below ≈50 K.

A mechanism on multiscale heterogenous deformation of nickel-based single crystal superalloys unraveled by time-of-flight neutron diffraction technology

Time-of-flight (TOF) neutron diffraction technology is a powerful tool for acquiring rich diffraction information on the multiscale microstructures and stresses of nickel-based single crystal superalloys. In this study, the tensile deformation behaviors of DD426 superalloy at 760 °C were investigated by TOF neutron diffraction. Combined with electron backscatter diffraction technology, the multiscale deformation heterogeneity between γ/γ' phases and dendritic/interdendritic regions was simultaneously characterized for the first time. Our experiments revealed a significant misorientation difference and the existence of a long-range stress field in the adjacent area between the dendritic and interdendritic regions after tensile deformation at 760 °C. The misorientation angles of crystal planes along the loading direction between the dendritic and interdendritic regions in the deformed alloy was approximately 1.6 ± 0.6° This misorientation can be attributed to the geometrically necessary dislocations (GNDs) concentrated in the adjacent area between the two regions with densities of approximately 1014 m-2. In addition, the lattice strains of both γ' and γ showed a compressive–tensile transition from the dendritic to interdendritic regions, balanced with a long-range stress field. The pile-up GNDs in the adjacent area between the two regions contributed to the existence of long-range stress fields. This study highlights that TOF neutron diffraction technology may reveal well the heterogeneous deformation mechanisms via the formation of both GNDs and pile-up in the adjacent interdendritic/dendritic area of single crystal superalloys.

Tuning structural modulation and magnetic properties in metal-organic coordination polymers [CH3NH3]CoxNi1-x(HCOO)3.

Three solid solutions of [CH3NH3]CoxNi1-x(HCOO)3, with x = 0.25 (1), x = 0.50 (2) and x = 0.75 (3), were synthesized and their nuclear structures and magnetic properties were characterized using single-crystal neutron diffraction and magnetization measurements. At room temperature, all three compounds crystallize in the Pnma orthorhombic space group, akin to the cobalt and nickel end series members. On cooling, each compound undergoes a distinct series of structural transitions to modulated structures. Compound 1 exhibits a phase transition to a modulated structure analogous to the pure Ni compound [Cañadillas-Delgado, L., Mazzuca, L., Fabelo, O., Rodríguez-Carvajal, J. & Petricek, V. (2020). Inorg. Chem. 59, 17896-17905], whereas compound 3 maintains the behaviour observed in the pure Co compound reported previously [Canadillas-Delgado, L., Mazzuca, L., Fabelo, O., Rodriguez-Velamazan, J. A. & Rodriguez-Carvajal, J. (2019). IUCrJ, 6, 105-115], although in both cases the temperatures at which the phase transitions occur differ slightly from the pure phases. Monochromatic neutron diffraction measurements showed that the structural evolution of 2 diverges from that of either parent compound, with competing hydrogen bond interactions that drive the modulation throughout the series, producing a unique sequence of phases. It involves two modulated phases below 96 (3) and 59 (3) K, with different q vectors, similar to the pure Co compound (with modulated phases below 128 and 96 K); however, it maintains the modulated phase below magnetic order [at 22.5 (7) K], resembling the pure Ni compound (which presents magnetic order below 34 K), resulting in an improper modulated magnetic structure. Despite these large-scale structural changes, magnetometry data reveal that the bulk magnetic properties of these solid solutions form a linear continuum between the end members. Notably, doping of the metal site in these solid solutions allows for tuning of bulk magnetic properties, including magnetic ordering temperature, transition temperatures and the nature of nuclear phase transitions, through adjustment of metal ratios.

Magnetic ordering in the frustrated pyrochlore Yb2Ru2O7

Yb2Ru2O7 was studied using neutron diffraction and muon spin relaxation measurements to investigate the effect of the Yb anisotropy and Yb-Ru exchange interaction on the magnetic ordering transitions in this material. The Ru moments order into a long range ordered state below 85 K, while the Yb moments start to freeze/order below 20 K, which is at a higher temperature as suggested by previous reported bulk measurements. No structural distortions are observed at the magnetic transitions. Representational analysis shows that the ordering of the Ru and Yb moments can be described by the same irreducible representation. The two magnetic sublattices are, however, antiferromagnetically coupled. Unlike what has been suggested by bulk measurements and has been observed in other members of this family of Ru pyrochlores, the Yb single ion planar anisotropy, surprisingly, does not influence the Ru moment ordering. The ordering of the Ru moments, on the other hand, does influence freezing/ordering of the Yb moments.

Order-disorder phase transitions in Fe81Ga19-RE ALLOYS (RE = Dy, Er, Tb, Yb) according to neutron diffraction data

New data on the phase compositions and structural transformations in a number of Fe81Ga19 alloys doped with trace amount (≤ 0.2 at.%) of rare earth elements are presented. The data are obtained in neutron diffraction experiments performed with high resolution and in continuous temperature scanning mode when heated to 900 °C and subsequent cooling. It has been established that structural rearrangements proceed in a generally identical manner both in the original Fe81Ga19 alloy and in its doped analogues. Slow heating and subsequent cooling of the alloys (rate ±2 °C/min) leads to the formation of clusters of the D03 phase with sizes in the range (200–300) Å in the matrix of the disordered A2 phase. The sizes and volume fraction of clusters (~0.3 of the sample volume) weakly depend on the specific composition. The degree of ordering of the clusters atomic structure changes with temperature according to a second-order phase transition and is close to unity at room temperature. The search for structural ordering corresponding to the modified D03 phase, discovered in a number of electron diffraction studies, did not lead to a positive result.

2D to 3D Magnetism in Synthetic Micas.

Fe-based mica minerals usually display two opposing magnetic ground states, either they behave as spin-glasses or as layered ferrimagnets. No definite reason has been proposed as an explanation for this duality. This conundrum is unraveled by comparing the synthetic micas KFe3[MGe3]O10X2 with M═Fe and Ga, X═OH- and F-. Neutron diffraction demonstrates a 2D to 3D magnetic transition in KFe3[FeGe3]O10(OH)2 while just hints or no order at all are observed for the fluorides with M═Fe and Ga respectively. The 3D transition is triggered by the presence of iron in the intralayer tetrahedra. DFT+U calculations show that the magnetic exchange couplings between the previously believed solely magnetic octahedral layers would otherwise be frustrated without this intralayer iron.

Potassium- and Lithium-Ammonia Intercalation into Excitonic Insulator Candidate Ta2NiSe5.

Two new reduced phases derived from the topical excitonic insulator candidate Ta2NiSe5 have been synthesized via the intercalation of lithium and potassium from solutions of the metals in liquid ammonia. Li(NH3)Ta2NiSe5 and KTa2NiSe5 both crystallize in orthorhombic space group Pmnb with the following lattice parameters: a = 3.5175(1) Å, b = 18.7828(7) Å, and c = 15.7520(3) Å and a = 3.50247(3) Å, b = 13.4053(4) Å, and c = 15.7396(2) Å, respectively. They have increased unit cell volumes of 48% and 31%, respectively, relative to that of Ta2NiSe5. Significant rearrangement of the transition metal selenide layers is observed in both intercalates compared to the parent phase. In Li(NH3)Ta2NiSe5, neutron diffraction experiments confirm the location of the light Li, N, and H atoms, and solid-state nuclear magnetic resonance (NMR) experiments show that H, N, and Li each occupy a single environment at ambient temperature on the NMR time scale. Magnetometry data show that both intercalates have increased magnetic susceptibilities relative to that of Ta2NiSe5, consistent with the injection of electrons during intercalation and an enhancement of the Pauli paramagnetism.

Influence of hydrogen on deformation and embrittlement mechanisms in a high Mn austenitic steel: In-Situ neutron diffraction and diffraction line profile analysis

Austenitic steels have relatively high resistance to hydrogen embrittlement and play a critical role in hydrogen service applications. In particular, high Mn austenitic steels are considered economically viable alloy alternatives for these applications. The current study employed in-situ and ex-situ neutron diffraction techniques combined with diffraction line profile analysis (DLPA) to investigate the influence of hydrogen on deformation and embrittlement mechanisms in a high Mn (approximately 30 wt pct) austenitic steel. Investigation using both neutron diffraction and electron backscatter diffraction revealed the presence of extensive deformation twins and stacking faults within the steel microstructure after tensile deformation in the non-charged condition. These microstructural features suggest planar deformation behavior, which is expected from the relatively low stacking fault energy (SFE) of the alloy (approximately 29 mJ/m2). Hydrogen pre-charging resulted in apparent increases in both dislocations and stacking faults, contributing to macroscopic hardening and embrittlement mechanisms. Overall, numerical parameters obtained through neutron DLPA were used to elucidate the underlying mechanisms associated with hydrogen effects on the mechanical behavior, i.e. macroscopic strengthening, strain hardening rate, and embrittlement.

Synthesis and Electrochemical Performance of High‐Entropy Spinel‐Type Oxides Derived from Multimetallic Polymeric Precursors

High‐entropy spinel‐type oxides are synthesized by a modified Pechini process, wet chemistry approach, and solid‐state synthesis method and characterized as anode materials for Li‐ion batteries. The Pechini process that involves chelation and polyesterification reactions facilitates the formation of high‐entropy spinel‐type oxides without compositional segregation at ≈600 °C as confirmed by in situ and ex situ XRD. XAFS analysis and the Rietveld refinement of room‐temperature neutron diffraction data suggest the composition (Mn0.05Fe0.48Co0.47, tetrahedral)(Cr0.61Mn0.52Fe0.11Co0.09Ni0.68, octahedral)O4 for phase‐pure specimens. Compared to high‐entropy spinel‐type oxides synthesized by the solid‐state method, the precursor‐derived materials demonstrate higher specific capacity as anodes, in which the materials without citric acid addition exhibit low capacity fading at high current densities and maintained a capacity of ≈200 mAh g−1 after 1000 cycles. The generation of a rock‐salt‐type phase during cycling is confirmed for the first time by in situ charging–discharging XRD. The charging–discharging of this anode material is achieved mainly through the embedding–disembedding of lithium ions in the lattice of the generated rock‐salt‐type phase.

Analysis of magnetic structures in JANA2020.

JANA2020 is a program developed for the solution and refinement of regular, twinned, modulated, and composite crystal structures. In addition, JANA2020 also includes a magnetic option for solving magnetic structures from powder and single-crystal neutron diffraction data. This tool uses magnetic space and superspace symmetry to describe commensurate and incommensurate magnetic structures. The basics of the underlying formulation of magnetic structure factors and the use of magnetic symmetry for handling modulated and non-modulated magnetic structures are presented here, together with the general features of the magnetic tool. Examples of structures solved in the magnetic option of JANA2020 are given to illustrate the operation and capabilities of the program.

Unique magnetic structure of the vdW antiferromagnet VBr3

VBr3 is a van der Waals antiferromagnet below the Néel temperature of 26.5 K with a saturation moment of 1.2 µB/f.u. above the metamagnetic transitions detected in the in-plane and out-of-plane directions. To reveal the AFM structure of VBr3 experimentally, we performed a single-crystal neutron diffraction study on a large high-quality crystal. The collected data confirmed a slight monoclinic distortion of the high-temperature rhombohedral structure below 90 K. The magnetic structure was, nevertheless, investigated within the R-3 model. The antiferromagnetic structure propagation vector k = (1, 0, ½) was revealed. In an attempt to determine the magnetic structure, 72 non-equivalent magnetic reflections were recorded. The experimental data were confronted with the magnetic space groups dictated by the R-3 lattice symmetry and propagation vector. The best agreement between the experimental data and the magnetic structure model was obtained for the space group P-1.1′_c. The magnetic unit cell of the proposed unique antiferromagnetic structure with periodicity 6c is built from two identical triple layers antiferromagnetically coupled along the c axis. Each triple layer comprises a Néel antiferromagnetic monolayer sandwiched between two antiferromagnetically coupled ferromagnetic monolayers.

Low-dimensional metal-organic frameworks: a pathway to design, explore and tune magnetic structures.

The magnetic structure adopted by a material relies on symmetry, the hierarchy of exchange interactions between magnetic ions and local anisotropy. A direct pathway to control the magnetic interactions is to enforce dimensionality within the material, from zero-dimensional isolated magnetic ions, one-dimensional (1D) spin-chains, two-dimensional (2D) layers to three-dimensional (3D) order. Being able to design a material with a specific dimensionality for the phenomena of interest is non-trivial. While many advances have been made in the area of inorganic magnetic materials, organic compounds offer distinct and potentially more fertile ground for material design. In particular magnetic metal-organic frameworks (mMOFs) combine magnetism with non-magnetic property functionality on the organic linkers within the structural framework, which can further be tuned with mild perturbations of pressure and field to induce phase transitions. Here, it is examined how neutron scattering measurements on mMOFs can be used to directly determine the magnetic structure when the magnetic ions are in a 2D layered environment within the wider 3D crystalline framework. The hydrated formate, in deuterated form, Co(DCOO)2·2D2O, which was one of the first magnetic MOFs to be investigated with neutron diffraction, is reinvestigated as an exemplar case.

Understanding the High-Temperature Deformation Behaviors in Additively Manufactured Al6061+TiC Composites via In Situ Neutron Diffraction

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.