Neutron Diffraction Research Articles

Residual Stress Measurement of Laser Powder Bed Fusion Additively Manufactured Hastelloy-X Through Crystal Plasticity Simulations and Neutron Diffraction Experiments

Residual Stress Measurement of Laser Powder Bed Fusion Additively Manufactured Hastelloy-X Through Crystal Plasticity Simulations and Neutron Diffraction Experiments

Oxygen Vacancy and Bandgap Simultaneous Modulation to Achieve High Lithiophilicity and Mechanical Strength of Lithium Metal Anodes.

Metal oxides with conversion and alloying mechanisms are more competitive in suppressing lithium dendrites. However, it is difficult to simultaneously regulate the conversion and alloying reactions. Herein, conversion and alloying reactions are regulated by modulation of the zinc oxide bandgap and oxygen vacancies. State-of-the-art advanced characterization techniques from a microcosmic to a macrocosmic viewpoint, including neutron diffraction, synchrotron X-ray absorption spectroscopy, synchrotron X-ray microtomography, nanoindentation, and ultrasonic C-scan demonstrated the electrochemical gain benefit from plentiful oxygen vacancies and low bandgaps due to doping strategies. In addition, high mechanical strength 3D morphology and abundant mesopores assist in the uniform distribution of lithium ions. Consequently, the best-performed ZnO-2 offers impressive electrochemical properties, including symmetric Li cells with 2000h and full cells with 81% capacity retention after 600 cycles. In addition to providing a promising strategy for improving the lithiophilicity and mechanical strength of metal oxide anodes, this work also sheds light on lithium metal batteries for practical applications.

Anomalous magnetic and electrical properties of disordered double perovskite alloy LaCaMnFeO6

Double perovskite alloys are of significant interest owing to their intriguing magnetic properties and potential practical applications. In this study, we provided a detailed report on the structural, electrical and magnetic features of the double perovskite LaCaMnFeO6, prepared via the conventional solid-state reaction technique. Neutron diffraction analysis showed that the sample is single-phase adopting the Pnma orthorhombic structure with random distribution of La3+/Ca2+ and Mn4+/Fe3+ ions on A- and B-sites, respectively. A long-range G-type antiferromagnetic order was formed below T N = 250 K. Magnetic measurements unveiled a cluster glassy behavior at low temperatures with a complex distribution of cluster magnetic anisotropy energy. Ferromagnetic clusters consisting of two Mn4+ and one Fe3+ were found to exist in the paramagnetic phase. The complex magnetic properties of LaCaMnFeO6 are attributed to the cation disorder effect combined with the competition between magnetic interactions. Unusual electrical behavior with a large positive magnetoresistive effect was observed and correlated to magnetic phase transitions.

Anharmonic incommensurate structure modulation in Ni-Mn-Ga martensite exhibiting highly mobile twin boundaries

We perform neutron diffraction on a bulk Ni50.0Mn27.5Ga22.5 single crystal to investigate the evolution of its five-layered modulated (10M) martensite structure, from 300 K down to 10 K. Close to martensite transformation, the modulation is nearly commensurate, with q = 0.402 in a modulation vector (q, q, 0). Upon cooling, the shift in diffraction satellites indicates a transition to an incommensurate modulation with increasing q. However, the observed fifth-order diffraction satellites below 260 K and even more complex satellite landscape at 10 K cannot be explained by incommensurability alone. Our analysis reveals that the modulation function is highly anharmonic, encompassing Fourier components up to the eighth order. We have developed a single-parameter description of the evolution of modulation across the entire temperature interval of the 10M phase existence. Surprisingly, the structure evolution from commensurate to incommensurate modulation has no significant effect on twin boundary mobility.

Magnetic structures in R5Pt2In4 (R = Tb-Tm) investigated by neutron powder diffraction.

Results of the neutron powder diffraction measurements carried out for R5Pt2In4 (R = Tb-Tm) are reported. The compounds crystallize in an orthorhombic crystal structure of the Lu5Ni2In4-type with the rare earth atoms occupying three different sublattices. Neutron diffraction data reveal that at low temperatures the rare earth magnetic moments order below the critical temperature equal to 105, 93, 28, 12 and 3.8 K for R = Tb, Dy, Ho, Er and Tm, respectively. With decreasing temperature the rare earth magnetic moments at the 2a and 4g2 sites order first, while the moments at the 4g1 site order at lower temperatures. Ferrimagnetic order along the c axis, described by the propagation vector k1 = [0, 0, 0], develops in Tb5Pt2In4 below the Curie temperature (TC = 105 K). At lower temperatures, an antiferromagnetic component in the ab plane appears. The component is incommensurate with the crystal structure (k2 = [0, 0.66, ½]), but it turns into a commensurate one (k3 = [0, 0, ½]) with decreasing temperature. Antiferromagnetic order along the c axis, described by k4 = [½, 0, 0], is found in Dy5Pt2In4 below the Néel temperature (TN = 93 K). The k4-related component disappears below 80 K and the magnetic structure transforms into a ferro/ferrimagnetic one described by k1 = [0, 0, 0]. Further decrease in temperature leads to the appearance of an incommensurate antiferromagnetic component within the ab plane below 10 K (k2 = [0, 0.45, ½]), which finally turns into a commensurate one (k5 = [0, ½, ½]). In Ho5Pt2In4, a sine-modulated magnetic structure with moments parallel to the c axis (k6 = [⅓,0,0]) is observed below 28 K. With a decrease in temperature, new components, related to k1 = [0, 0, 0] (bc plane) and k4 = [½, 0, 0] (c axis), appear. The coexistence of two orderings - in the ab plane (k1 = [0, 0, 0]) and a modulated one with moments along the b axis (k7 = [kx, 0, 0]) - is found in Er5Pt2In4 below 12 K. Decreasing temperature leads to the order-order transformation of the k1-related component to another one with magnetic moments still constrained to the ab plane and preserved value of the propagation vector (i.e. k1 = [0, 0, 0]). Tm5Pt2In4 orders antiferromagnetically below TN = 3.8 K. Thulium magnetic moments lie in the ab plane, while the magnetic structure is described by k5 = [0, ½ , ½]. The direction of magnetic moments depends on the rare earth element involved and indicates an influence of single ion anisotropy resulting from interaction with the crystalline electric field.

Hydrogen bond symmetrisation in D2O ice observed by neutron diffraction

Hydrogen bond symmetrisation is the phenomenon where a hydrogen atom is located at the centre of a hydrogen bond. Theoretical studies predict that hydrogen bonds in ice VII eventually undergo symmetrisation upon increasing pressure, involving nuclear quantum effect with significant isotope effect and drastic changes in the elastic properties through several intermediate states with varying hydrogen distribution. Despite numerous experimental studies conducted, the location of hydrogen and hence the transition pressures reported up to date remain inconsistent. Here we report the atomic distribution of deuterium in D2O ice using neutron diffraction above 100 GPa and observe the transition from a bimodal to a unimodal distribution of deuterium at around 80 GPa. At the transition pressure, a significant narrowing of the peak widths of 110 is also observed, attributed to the structural relaxation by the change of elastic properties.

High Proton Conduction in the Octahedral Layers of Fully Hydrated Hexagonal Perovskite-Related Oxides.

Proton conductors have potential applications such as fuel cells, electrolysis cells, and sensors. These applications require new materials with high proton conductivity and high chemical stability at intermediate temperatures. Herein we report a series of new hexagonal perovskite-related oxides, Ba5R2Al2SnO13 (R = Gd, Dy, Ho, Y, Er, Tm, and Yb). Ba5Er2Al2SnO13 exhibited a high proton conductivity without chemical doping (e.g., 0.01 S cm-1 at 303 °C), which is attributed to its high proton concentration and diffusion coefficient. The high diffusion coefficient of Ba5Er2Al2SnO13 can be attributed to the fast proton migration in the octahedral layers. The high proton concentration is attributed to full hydration in hydrated Ba5Er2Al2SnO13 and the large amount of intrinsic oxygen vacancies in the dry sample, as evidenced by both neutron diffraction and thermogravimetric analysis. Ba5Er2Al2SnO13 was found to exhibit high chemical stability under wet atmospheres of O2, air, H2, and CO2. High proton conductivity and high chemical stability indicate that Ba5Er2Al2SnO13 is a superior proton conductor. Ba5R2Al2SnO13 (R = Gd, Dy, Ho, Y, Tm, and Yb) exhibited high electrical conductivity in wet N2, suggesting that these materials also exhibit high proton conductivity. These findings will open new avenues for proton conductors. The high proton conductivity via full hydration and fast proton migration in octahedral layers in highly oxygen-deficient hexagonal perovskite-related materials would be an effective strategy for developing next-generation proton conductors.

Significant Enhancement of Negative Thermal Expansion Under Low Pressure in Cu2P2O7.

Much effort is made to achieve the negative thermal expansion (NTE) control, but rare methods reached the improvement of intrinsic NTE. In the present work, a significantly enhanced NTE is realized in Cu2P2O7 by applying low pressure. Especially, the volumetric coefficient of thermal expansion (CTE) of Cu2P2O7 reached to -50.0×10-6 K-1 (150-325K) under 0.25GPa, which is increased by 47.5% compared to its NTE in a similar temperature range under atmosphere pressure. This character enables a more effective manifestation of the thermal compensation role of Cu2P2O7 in composites. The enhanced NTE mechanisms are analyzed by high pressure synchrotron X-ray diffraction, neutron diffraction at variable temperature and pressure, as well as density functional theory (DFT) calculations. The results show that applied pressure accelerates the contraction of the distance between adjacent CuO layers and CuO columns. Meanwhile, the low-frequency phonon contribution to NTE in α-Cu2P2O7 is improved. This work is meaningful for the exploration of methods to enhance NTE and the practical application of NTE materials.

Violation of a Leggett-Garg Inequality Using Ideal Negative Measurements in Neutron Interferometry.

Leggett-Garg inequalities (LGIs) have been proposed in order to assess how far the predictions of quantum mechanics defy "macroscopic realism." With LGIs, correlations of measurements performed on a single system at different times are described. We report on an experiment that demonstrates the violation of an LGI with neutrons. The final measured value of the Leggett-Garg correlator K=1.120±0.007(stat)±0.019(sys), obtained in a neutron interferometric experiment, is clearly above the limit K=1 predicted by macrorealistic theories. The experimental results are analyzed within the framework of dynamical theory of neutron diffraction, evidently reproducing the obtained values.

Magnetic ground state of NdB4 : Interplay between anisotropic exchange interactions and hidden order on a Shastry-Sutherland lattice

The neodymium tetraboride NdB4, crystalizing into a tetragonal crystal structure, has the magnetic ions located on a Shastry-Sutherland lattice. The compound undergoes several magnetic phase transitions and exhibits a complex multi-k ground state that has so far been elusive. Here we report the solution and quantitative refinement of the magnetic ground state of NdB4 based on neutron diffraction data. The magnetic structure consists of two separate components; one of them is confined within the ab plane and makes an orthogonal all-in-all-out spin configuration maintaining translation symmetry of the crystal. Another is pointing along the c axis, and this component forms an anharmonic spin density wave consisting of three-up-two-down sequences with fivefold periodicity. The in-plane and out of plane spin structures represent distinct magnetic instabilities which normally would not coexist. Their simultaneous presence in the same phase is an interesting phenomenon associated with anisotropic exchange interactions and coupling to a symmetry breaking nonmagnetic order parameter undetectable by the available diffraction data. Published by the American Physical Society 2024

In situ study of phase transformations in the metastable Fe-42Ga alloy

The evolution of the structural phases of the Fe-42.4 at% Ga alloy was studied using neutron diffraction performed with high-intensity continuous scanning in a wide temperature range. The sequence of occurrence of structural states both during heating and subsequent cooling is reported. The structural phases Fe13Ga13, Fe13Ga9, α-Fe6Ga5, D03, L12, A2 are present in the alloy and they disappear upon heating above 800 °C into the partially ordered B2/A2 phase. The high-temperature Fe13Ga13 intermetallic compound exists in two temperature ranges: 25–580 °С and 770–800 °С during heating and precipitates again during cooling. The persistence of the phase upon cooling down to room temperature is inconsistent with the phase diagram, indicating that the alloy remains in a metastable state after the heating and subsequent cooling. The D03, α-Fe6Ga5 and L12 phases are formed during cooling.

Microstructural Evolution of Tantalum During Deformation and Subsequent Annealing

Microstructure-aware models are necessary to predict the behavior of material based on process knowledge or to extrapolate mechanical properties of materials to environmental conditions which are not easily reproduced in the laboratory, e.g., nuclear reactor environments. Elemental Ta provides a relatively simple BCC system in which to develop a microstructural understanding of deformation processes which can then be applied to more complicated BCC alloys. In situ neutron diffraction during compressive deformation and subsequent heat treatment have been used to monitor the evolution of microstructural features in Ta throughout simulated processing steps. Crystallographic texture and dislocation density are determined as a function of first plastic strain, then temperature. Lattice strains are determined and attributed to stresses at macroscopic, grain and dislocation length scales. The increase of the dislocation density through deformation and subsequent recovery during heat treatment is monitored through the changing diffraction line profile. Also, randomization of the texture is used as a signature of recrystallization. The recovery of dislocations through annihilation is not observed to depend on the initial dislocation density in the range studied here. In contrast, recrystallization is observed to depend strongly on the initially dislocation density.

Single-crystal neutron diffraction study on the Ho13.6Au61.1Al25.3 quasicrystal approximant

A single-crystal neutron diffraction study was conducted on a Ho13.6Au61.1Al25.3 Tsai-type quasicrystal approximant synthesised by the self-flux method. The magnetisation measurements reveal a ferrimagnetic behaviour with a transition below 6 K. In agreement with the magnetometry data, a non-coplanar whirling spin order in the icosahedral clusters around the crystallographic [1 1 1] direction with a ferrimagnetic arrangement was observed from single-crystal neutron diffraction measurements below 5.5 K. The magnetic structure of Ho13.6Au61.1Al25.3 is compared to the previously published magnetic structures of related RE-Au-SM (RE = Tb and Ho; SM = Al, Si and Ga) systems.

Investigating the flux pinning dependence on grain orientation in YBa2Cu3O7−δ using neutron tomography

In this study, we report the first case of non-destructive characterization of the dependence of the flux trapping mechanism on the grain properties of a bulk type II superconductor using a combination of polarized neutron tomography and diffraction contrast tomography. The high temperature superconductor, YBa2Cu3O7−δ, has been used in this study due to its viable commercial growth processes typically resulting in the production of polycrystalline specimens. The diffraction tomography revealed the pseudo-single crystal nature of the sample i.e. a polycrystalline sample with 47 composite grains having a maximum grain misorientation angle of 1.86°. Polarized neutron tomography was used for characterization of the flux trapped in the material after field cooling to 90.5 K in a field of 0.5 mT and switching off the field. A combination of the results from these two non-destructive characterization techniques indicate a correlation between the anisotropy of the trapped flux with the orientation of the grains in the material in addition to a preference for the flux trapping in the grain boundaries.

Disorder induced band gap lowering in kesterite type Cu2ZnSnSe4 and Ag2ZnSnSe4: a first-principles and special quasirandom structures investigation

Quaternary chalcogenides, i.e. Cu2ZnSnS4, crystallising in the kesterite crystal structure have already been demonstrated as potential building blocks of thin film solar cells, containing only abundant elements and exhibiting power conversion efficiencies of about 14.9% so far. However, due to the potential presence of several structurally similar polymorphs, the unequivocal identification of their ground state crystal structures required the application of more elaborate neutron diffraction experiments. One particular complication arose from the later identified Cu–Zn disorder, present in virtually all thin film samples. Subsequently, it has been shown experimentally that this unavoidable Cu–Zn disorder leads to a band gap lowering in the respective samples. Additional theoretical investigations, mostly based on Monte-Carlo methods, tried to understand the atomistic origin of this disorder induced band gap lowering. Here, we present theoretical results from first-principles calculations based on density functional theory for the disorder induced band gap lowering in kesterite Cu2ZnSnSe4 and Ag2ZnSnSe4, where the Cu–Zn and Ag–Zn disorder is modelled via a supercell approach and special quasirandom structures. Results of subsequent analyses of structural, electronic, and optical properties are discussed with respect to available experimental results, and will provide additional insight and knowledge towards the atomistic origin of the observed disorder induced band gap lowering in kesterite type materials.

Structural, physical and thermal properties of lead germanate glasses

The effects of PbO concentration on the density, thermal and structural properties of xPbO–(100-x)GeO2 (x = 20 to 55 mol%) glasses were studied. Density of glasses increases linearly from 5.043 to 6.981(5) g·cm−3, while the glass transition temperature decreases drastically from 467 °C to 359 °C on increasing PbO concentration from 20 to 55 mol%. Neutron diffraction studies found that Ge-O co-ordination is in the range: 3.9–4.2(1), and there is a very weak germanate co-ordination anomaly at PbO concentration of 40 and 50 mol%. GeO4 are the dominant structural units with a small quantity of GeO3 and GeO5 but very little GeO6 in the glass network. Pb-O and OO co-ordination decreases with an increase in PbO mol% and are in the range of: 4.0–3.1(1) and 6.3–5.4(1) respectively. Raman studies indicate a decrease in Pb-O co-ordination with increase in PbO mol%, in good agreement with the neutron diffraction findings.

Interplay between D019, L12 and D03 phases in Fe3Ga-type alloy

Analysis of the first-order transition between D03 and two close-packed phases (L12, D019) in Fe3Ga-type alloy (26.9 %Ga), is carried out at different cooling rates from the range of equilibrium D019 phase and at different cooling rates from the range of equilibrium A2 phase. The structure was controlled by neutron diffraction, SEM-EBSD and additionally characterized using VSM and ATP tests. The obtained results clarify kinetics of D019 phase growth and transition to low temperature equilibrium L12 phase. We demonstrated that D019 phase is ferromagnetic at room temperature with very low saturation magnetostriction.

(Ca0.5Mn0.5)2MnTeO6 - An Anomalously Stable High-Pressure Double Perovskite.

High pressure high temperature treatments of the composition CaMnMnTeO6 are found to yield only an A2BB'O6-type double perovskite (Ca0.5Mn0.5)2MnTeO6, rather than a AA'BB'O6 double double perovskite with A- and B- site cation order as found in analogs CaMnMnReO6 and CaMnMnWO6 with similar cation sizes. Double perovskite (Ca0.5Mn0.5)2MnTeO6 adopts a monoclinic structure in space group P21/n with a framework of highly tilted MnO6 and TeO6 octahedra enclosing disordered Ca2+ and Mn2+ cations. Magnetic measurements show that (Ca0.5Mn0.5)2MnTeO6 is a highly frustrated spin glass with a freezing transition at 5 K, and no long-range spin order is apparent by neutron diffraction at 1.6 K.

Negative magnetization and magnetic ordering of rare earth and transition metal sublattices in NdFe0.5Cr0.5O3

We investigate the effect of alloying at the 3d transition metal site of a rare-earth-transition metal oxide, by considering NdFe0.5Cr0.5O3 mixed perovskite with two equal and random distribution of 3d ions, Cr and Fe, interacting with an early 4f rare earth ion, Nd. Employing temperature- and field- dependent magnetization measurements, temperature-dependent x-ray diffraction, neutron powder diffraction, and Raman spectroscopy, we characterize its structural and magnetic properties. Our study reveals bipolar magnetic switching (arising from negative magnetization) and magnetocaloric effect which underline the potential of the studied mixed perovskite in device application. The neutron diffraction study shows the absence of spin reorientation transition over the entire temperature range of 1.5–320 K, although both parent compounds exhibit spin orientation transition. We discuss the microscopic origin of this curious behavior. The neutron diffraction results also reveal the ordering of Nd spins at an unusually high temperature of about 40 K, which is corroborated by Raman measurements.

Ba4RuMn2O10: A Noncentrosymmetric Polar Crystal Structure with Disordered Trimers.

Phase-pure polycrystalline Ba4RuMn2O10 was prepared and determined to adopt the noncentrosymmetric polar crystal structure (space group Cmc21) based on results of second harmonic generation, convergent beam electron diffraction, and Rietveld refinements using powder neutron diffraction data. The crystal structure features zigzag chains of corner-shared trimers, which contain three distorted face-sharing octahedra. The three metal sites in the trimers are occupied by disordered Ru/Mn with three different ratios: Ru1:Mn1 = 0.202(8):0.798(8), Ru2:Mn2 = 0.27(1):0.73(1), and Ru3:Mn3 = 0.40(1):0.60(1), successfully lowering the symmetry and inducing the polar crystal structure from the centrosymmetric parent compounds Ba4T3O10 (T = Mn, Ru; space group Cmca). The valence state of Ru/Mn is confirmed to be +4 according to X-ray absorption near-edge spectroscopy. Ba4RuMn2O10 is a narrow bandgap (∼0.6 eV) semiconductor exhibiting spin-glass behavior with strong magnetic frustration and antiferromagnetic interactions.