Neutron Diffraction Experiments Research Articles

Simulating Crystal Structure, Acidity, Proton Distribution, and IR Spectra of Acid Zeolite HSAPO-34: A High Accuracy Study.

It is a challenge to characterize the acid properties of microporous materials in either experiments or theory. This study presents the crystal structure, acid site, acid strength, proton siting, and IR spectra of HSAPO-34 from the SCAN + rVV10 method. The results indicate: the crystal structures of various acid sites of HSAPO-34 deviate from the space group of R3¯; the acid strength inferred from the DPE value likely decreases with the proton binding sites at O(2), O(4), O(1),and O(3), contrary to the stability order in view of the internal energy; the calculated ensemble-averaged DPE is about 1525 kJ/mol at 673.15 K; and the proton siting and the proton distribution are distinctly influenced by the temperature: at low temperatures, the proton is predominantly located at O(3), while it prefers O(2) at high temperatures, and the proton at O(4) assumedly has the least distribution at 273.15-773.15 K. In line with the neutron diffraction experiment, a correction factor of 0.979 is needed to correct for the calculated hydroxyl stretching vibration (ν(O-H)) of HSAPO-34. It seems that the SCAN meta-GGA method, compensating for some drawbacks of the GGA method, could provide satisfying results regarding the acid properties of HSAPO-34.

Effects of Pre-Strain and Tempering on Mechanical Properties in High-Strength Martensitic Steels

Effects of pre-strain and tempering on mechanical properties in high-strength martensitic steels were investigated. In this study, strain tempering (ST) and quenching and tempering (QT) martensitic steels were prepared, and their mechanical properties were studied. In the tensile tests at the deformation temperatures between 296 and 573 K, the ST sample increased both of tensile strength (TS) and uniform elongation (U.El) from 473 to 523 K whereas the QT sample increased U.El with little change of TS. From the in situ neutron diffraction experiments, stress partitioning to the bcc phase increased with an increase in the deformation temperature from 296 to 523 K. The difference of phase stress between the bcc and cementite phases decreased with increasing the temperature because of a decrease in the cementite strength. In the ST sample, Pre-straining of 0.5% increased YS at 296 K with slight work hardening. The initial value of dislocation density (ρ) decreased at 523 K but ρ increased significantly after yielding, leading to better combination of TS and U.El. The combinations of pre-strain, tempering, and deformation temperatures have changed ρ before deformation and the increase of ρ after yielding of the martensitic steels.

Lipid bilayer properties potentially contributed to the evolutionary disappearance of betaine lipids in seed plants

BackgroundMany organisms rely on mineral nutrients taken directly from the soil or aquatic environment, and therefore, developed mechanisms to cope with the limitation of a given essential nutrient. For example, photosynthetic cells have well-defined responses to phosphate limitation, including the replacement of cellular membrane phospholipids with non-phosphorous lipids. Under phosphate starvation, phospholipids in extraplastidial membranes are replaced by betaine lipids in microalgae. In higher plants, the synthesis of betaine lipid is lost, driving plants to other strategies to cope with phosphate starvation where they replace their phospholipids by glycolipids.ResultsThe aim of this work was to evaluate to what extent betaine lipids and PC lipids share physicochemical properties and could substitute for each other. By neutron diffraction experiments and dynamic molecular simulation of two synthetic lipids, the dipalmitoylphosphatidylcholine (DPPC) and the dipalmitoyl-diacylglyceryl-N,N,N-trimethylhomoserine (DP-DGTS), we found that DP-DGTS bilayers are thicker than DPPC bilayers and therefore are more rigid. Furthermore, DP-DGTS bilayers are more repulsive, especially at long range, maybe due to unexpected unscreened electrostatic contribution. Finally, DP-DGTS bilayers could coexist in the gel and fluid phases.ConclusionThe different properties and hydration responses of PC and DGTS provide an explanation for the diversity of betaine lipids observed in marine organisms and for their disappearance in seed plants.

Development of 0.5 mm gauge size radial collimators for high-pressure neutron diffraction experiments at PLANET in J-PARC

Radial collimators with a 0.5 mm gauge size (GS) were specially designed for high-pressure neutron diffraction experiments. The performance and efficacy of these collimators, along with the 1.5 mm and 3.0 mm GS radial collimators, were investigated. The radial collimators with nominal GS of 0.75 mm, 1.5 mm, and 3.0 mm effectively exhibited GS of 0.50 mm, 1.07 mm, and 2.78 mm, respectively. The transmissions of all three radial collimators were deemed equivalent. The assessment using a Paris–Edinburgh (PE) press equipped with double-toroidal anvils and a diamond anvil cell (DAC) tailored for neutron diffraction revealed that the scattering intensity from the anvils was considerably minimized using the radial collimators and the sample-to-anvil signal ratio, as defined by the Bragg peak intensity ratio (IMgO220/IDiamond220), reached values of 0.5 and 2.0 for the PE press and DAC, respectively, when using the 0.5 mm GS radial collimators. These results indicate that the 0.5 mm GS radial collimators have been fabricated as intended and exhibit efficacy for the high-pressure-neutron diffraction experiments, specifically those exceeding 30 GPa, which cannot be reached with a PE press equipped with the standard double-toroidal anvils of a 1.5 mm cup diameter. Among those ever manufactured for neutron scattering experiments, the radial collimators display the smallest GS.

Slightly Hydrogen-Ordered State of Ice IV Evidenced by In Situ Neutron Diffraction.

Ice IV is a metastable high-pressure phase of ice in which the water molecules exhibit orientational disorder. Although orientational ordering is commonly observed for other ice phases, it has not been reported for ice IV. We conducted in situ powder neutron diffraction experiments for DCl-doped D2O ice IV to investigate its hydrogen ordering. We found abrupt changes in the temperature derivative of unit-cell volume, dV/dT, at ∼120 K, and revealed a slightly ordered structure at low temperatures based on the Rietveld method. The occupancy of the D1 site deviates from 0.5 in particular; it increased when samples were cooled at higher pressures and reached 0.174(14) at 2.38 GPa, 58 K. Our results evidence the presence of a low-symmetry hydrogen-ordered state corresponding to ice IV. It seems, however, difficult to experimentally access the completely ordered phase corresponding to ice IV by slow cooling at high pressure.

Operando analysis of the positive active mass of lead batteries by neutron diffraction

We have analysed, through neutron diffraction experiments with the volume-gauge technique, the operando performance of lead cells composed of industrial positive and negative electrodes, previously tank formed in the manufacturing plant. The cells, 6.7 cm × 11.5 cm in surface, comprised a 3.4 mm thick positive electrode sandwiched between two 2.3 mm thick negative electrodes. The electrolyte was sulphuric acid diluted in water, both deuterated, and the separators were industrial grade absorptive glass mat (AGM). The experiments, carried out using the VULCAN instrument at the Oak Ridge National Laboratory (TN, USA), showed the evolution of α-PbO2, β-PbO2 and PbSO4 phases in the positive active mass during charge/discharge cycling, comparing the behaviour of fresh and cycled cells. No evidence of PbSO4 phase in fully charged plates or PbO in any state of charge were found above 1% by weight. Significant inhomogeneity of phase distribution and transition rates inside the positive electrode was observed. The experiments allowed estimation of the energy efficiency by comparing the external energy provided to the cell with the energy stored in the PbSO4 to PbO2 transformations.

Deuterium Content and Site Occupancy in Iron Sulfide at High Pressure and Temperature Determined Using In Situ Neutron Diffraction Measurements

AbstractWe have performed in situ time‐of‐flight neutron diffraction experiments to examine the uptake of deuterium in iron monosulfide at pressures up to 11.4 GPa and temperatures to 1300 K. A D2 fluid was formed in the experiments through the decomposition of ND3BD3, resulting in an oxygen fugacity of approximately 1.2 log units below the iron‐wüstite buffer. Deuterium positions and site occupancies were determined in FeS V, using Rietveld refinements of the powder neutron diffraction patterns. Our structural model indicates that two normally unoccupied sites in the P63/mmc FeS V structure, at Wyckoff positions 6h and 4f, are partially occupied by D atoms, with the latter being more dominant. The deuterium content Dx in FeSDX increases with both pressure and temperature over the experimental conditions explored, from 0.126 (14) at 2.3 GPa and 787 K to 1.20 (16) at 9.7 GPa and 1300 K. The unit‐cell volume expansion per deuterium atom is 1.53 ± 0.16 Å3 at 6.9 GPa and 960 K, which is smaller than that determined for metallic iron phases at similar conditions. The variation in unit‐cell volume indicates that most deuterium is lost from FeS V upon temperature quenching at high‐pressures. By fitting the obtained FeS V deuterium site occupancies to a thermodynamic model, estimates for the hydrogen contents of iron monosulfide at conditions and oxygen fugacities consistent with the base of the cratonic lithosphere can be made. This results in values in the range of 1,700–2,700 ppm, which contribute to approximately 2–3 ppm hydrogen in the bulk mantle.

Atomic reconstruction induced by uniaxial stress in MnP

In condensed matter physics, pressure is frequently used to modify the stability of both electronic states and atomic arrangements. Under isotropic pressure, the intermetallic compound MnP has recently attracted attention for the interplay between pressure-induced superconductivity and complicated magnetic order in the vicinity . By contrast, we use uniaxial stress, a directional type of pressure, to investigate the effect on the magnetism and crystal structure of this compound. An irreversible magnetisation response induced by uniaxial stress is discovered in MnP at uniaxial stress as low as 0.04 text {GPa}. Neutron diffraction experiments reveal that uniaxial stress forms crystal domains that satisfy pseudo-rotational symmetry unique to the MnP-type structure. The structure of the coexisting domains accounts for the stress-induced magnetism. We term this first discovered phenomenon atomic reconstruction (AR) induced by uniaxial stress. Furthermore, our calculation results provide guidelines on the search for AR candidates. AR allows crystal domain engineering to control anisotropic properties of materials, including dielectricity, elasticity, electrical conduction, magnetism and superconductivity. A wide-ranging exploration of potential AR candidates would ensure that crystal domain engineering yields unconventional methods to design functional multi-domain materials for a wide variety of purposes.

Searching for a hydrogen-ordered counterpart of ice IV through in situ high-pressure powder neutron diffraction experiments

Searching for a hydrogen-ordered counterpart of ice IV through <i>in situ</i> high-pressure powder neutron diffraction experiments

Internal Elastic Strains of AZ31B Plate during Unloading at Twinning-Active Region

Magnesium alloys, being the lightest structural metals, have garnered significant attention in various fields. The characterization of inelastic behavior has been extensively investigated by researchers due to its impact on structural component performance. However, the occurrence of twinning in the absence of any applied driving force during unloading has lacked reasonable explanations. Moreover, the influence of deformation mechanisms other than twinning on inelastic behavior remains unclear. In this study, uniaxial tension and compression tests were conducted on hot-rolled magnesium alloy plates, and neutron diffraction experiments were employed to characterize the evolution of macroscopic mechanical response and microscopic mechanisms. Additionally, a twinning and detwinning (TDT) model based on the elastic visco-plastic self-consistent (EVPSC) model has been proposed, incorporating back stress to describe the deformation behavior during stress relaxation. This approach provides a comprehensive understanding of the inelastic behavior of magnesium alloys from multiple perspectives and captures the influence of microscale mechanisms. A thorough understanding of the inelastic behavior of magnesium alloys and a reasonable explanation for the occurrence of twinning under zero-stress conditions offer valuable insights for the precise design of magnesium alloy structures.

Revisiting the magnetic structure of Holmium at high pressure by using neutron diffraction

Low-temperature neutron diffraction experiments at P= 8 GPa have been conducted to investigate the magnetic structures of metallic Holmium at high pressures by employing a long d-spacing high-flux diffractometer and a Paris-Edinburgh press cell inside a cryostat. We find that at P=8 GPa and T=5 K, no nuclear symmetry change is observed, keeping therefore the hexagonal closed packed (hcp) symmetry at high pressure. Our neutron diffraction data confirm that the ferromagnetic state does not exist. The magnetic structure corresponding to the helimagnetic order, which survives down to 5 K, is fully described by the magnetic superspace group formalism. These results are consistent with those previously published using magnetization experiments.

Unraveling the magnetic structure of YbNiSn single crystal via crystal growth and neutron diffraction

Neutron and X-ray diffraction experiments were performed on the ternary intermetallic compound YbNiSn, formerly categorized as a ferromagnetic Kondo compound. At zero field, an increase in scattering intensity was observed on top of allowed and forbidden nuclear reflections below Tc, breaking the reflection condition of the crystal symmetry Pnma. This indicates that the magnetic structure of YbNiSn is antiferromagnetic-type, rather than the previously proposed simple collinear ferromagnetic structure. Temperature dependence of the scattering intensity of the 011 reflection confirmed the magnetic ordering at 5.77(2) K. No incommensurate satellite reflection was observed at 2.5 K. By applying external magnetic field of 1 T along the a axis, the magnetic intensity at the nuclear-forbidden 001 position was suppressed, while a slight enhancement at the nuclear-allowed 002 position was observed. This suggests a spin-flip transition under the external magnetic field along the a axis in YbNiSn. The proposed magnetic structures at zero field and 1 T correspond to the magnetic space groups of Pn'm'a and Pnm'a', respectively. The piezomagnetic effect and the switch between the two magnetic space groups by the external stress, which could be detected by the anomalous Hall effect, are proposed.

3D Investigation of Damage During Strain‐Controlled Thermomechanical Fatigue of Cast Al–Si Alloys

The strain‐controlled thermomechanical fatigue behavior is investigated for three cast near‐eutectic Al–Si alloys with different Ni, Cu, and Mg contents. Synchrotron tomography and neutron diffraction experiments are used to correlate 3D microstructural features with damage initiation and evolution. The results show that the alloy with lower Cu, Ni, and Mg concentrations has up to 45% higher thermomechanical fatigue resistance for cooling/heating rates of 5 and 15 K s−1. In addition, this alloy also exhibits damage formation at later stages during thermomechanical fatigue and slower damage accumulation compared to other alloys. This difference in behavior is a consequence of its higher ductility, which is a result of the lower volume fraction and global interconnectivity of the 3D hybrid networks formed by Si and intermetallics and the absence of large primary Si clusters which act as preferred crack initiation sites during the early stages of thermomechanical fatigue.

A correlation between texture evolution and dislocation density in Al-Mg alloys during uniaxial tensile deformation

In this study, the studies of texture evolution and dislocation density in Al-Mg alloys during uniaxial tensile deformation was performed by the neutron diffraction experiment. During tensile deformation under low strain rate (1.33 × 10−5 s−1), the 〈001〉 and 〈111〉 duplex texture was observed in Al-Mg alloys. The differences of pole density at 〈001〉 and 〈111〉 orientations depend on the content of Mg addition. The 〈001〉 deformation texture was developed from initial 〈001〉 cube texture, especially observed in the alloys with low Mg addition and pure Al sample. In alloys with high Mg addition, the development of 〈111〉 texture was clearly presented. An increase in Mg addition induced larger dislocation density during the deformation in a correlation with the formation of 〈111〉 deformation texture.

Effects of Loading Direction on the Anisotropic Tensile Properties of Duplex Stainless Steels Based on Phase Strains Obtained by In Situ Neutron Diffraction Experiments

Effects of Loading Direction on the Anisotropic Tensile Properties of Duplex Stainless Steels Based on Phase Strains Obtained by In Situ Neutron Diffraction Experiments

Neutron diffraction studies under zero and finite magnetic fields of the 12 quantum magnetization plateau compound Ni2V2O7

We performed powder neutron diffraction experiments on a $\frac{1}{2}$ quantum magnetization plateau compound ${\mathrm{Ni}}_{2}{\mathrm{V}}_{2}{\mathrm{O}}_{7}$ for magnetic fields in the range 0--10 T. The incommensurate magnetic structures with the propagation vector $({k}_{x}\ensuremath{\sim}0.45,0,0)$ were determined at 0 T and at 6.0 K (between ${T}_{\mathrm{N}1}=6.7$ K and ${T}_{\mathrm{N}2}=5.7$ K) and 2.3 K. Consequently, the Ni1 and Ni2 moments were disordered and ordered at 6.0 K, respectively, indicating a partially disordered state. The magnetic structure of Ni2 moments was a spin density wave structure with moments ordered parallel to the $b$ axis and perpendicular to the propagation vector. Both Ni1 and Ni2 moments exhibited ellipsoidal cycloidal incommensurate magnetic structures at 2.3 K. These moments lay in the $ab$ plane. The maximum magnitudes of Ni1 and Ni2 moments [1.62(16) and 2.50(6) ${\textmu{}}_{\mathrm{B}}$] at 2.3 K were sufficiently smaller and slightly larger than the value ($\ensuremath{\sim}2.2\phantom{\rule{0.28em}{0ex}}{\textmu{}}_{\mathrm{B}}$) expected from the classical picture. Further, we evaluated the field-induced magnetic moments as follows: ${m}_{1}=0.3$ and ${m}_{2}=1.9\phantom{\rule{0.28em}{0ex}}{\textmu{}}_{\mathrm{B}}$ at Ni1 and Ni2 sites, respectively, at 10 T and 1.9 K, where the $\frac{1}{2}$ quantum magnetization plateau was observed. The results indicating both the ordered moment at 0 T and the field-induced moment at 10 T being small and large at Ni1 and Ni2 sites, respectively, were consistent with results expected in the $\text{dimer}+\text{monomer}$ model that was proposed by J. J. Cao et al. [Phys. Rev. B 106, 184409 (2022)].

Interplay between Magnetism and Topology: Large Topological Hall Effect in an Antiferromagnetic Topological Insulator, EuCuAs.

Magnetic interactions in combination with nontrivial band structures can give rise to several exotic physical properties such as a large anomalous Hall effect, the anomalous Nernst effect, and the topological Hall effect (THE). Antiferromagnetic (AFM) materials exhibit the THE due to the presence of nontrivial spin structures. EuCuAs crystallizes in a hexagonal structure with an AFM ground state (Néel temperature ∼ 16 K). In this work, we observe a large topological Hall resistivity of ∼7.4 μΩ-cm at 13 K which is significantly higher than the giant topological Hall effect of Gd2PdSi3 (∼3 μΩ-cm). Neutron diffraction experiments reveal that the spins form a transverse conical structure during the metamagnetic transition, resulting in the large THE. In addition, by controlling the magnetic ordering structure of EuCuAs with an external magnetic field, several fascinating topological states such as Dirac and Weyl semimetals have been revealed. These results suggest the possibility of spintronic devices based on antiferromagnets with tailored noncoplanar spin configurations.

Magnetic properties of the quasicrystal approximant Au65Ga21Tb14

The magnetic properties of the quasicrystal approximant ${\mathrm{Au}}_{65}{\mathrm{Ga}}_{21}{\mathrm{Tb}}_{14}$ were investigated using magnetization and neutron diffraction experiments. The temperature dependences of the magnetic susceptibility and magnetization curve indicate dominant ferromagnetic interactions, whereas a whirling antiferromagnetic order was observed in neutron diffraction experiments. In the antiferromagnetic phase, the magnetic moments are aligned almost perpendicular to a pseudofivefold symmetry axis, which corresponds to the easy-axis direction of a Tb atom. Magnetic properties similar to those of ${\mathrm{Au}}_{72}{\mathrm{Al}}_{14}{\mathrm{Tb}}_{14}$ in spite of the substantial difference in the Au concentration suggest the robustness of the easy-axis anisotropy against the chemical environment.

On the dependence of creep-induced dislocation configurations on crystallographic orientation in pure Al and Al-Mg.

The peak broadening in neutron diffraction experiments on tensile specimens of pure Al (99.8%) and an Al-Mg alloy pre-deformed at different creep strains is analysed. These results are combined with the kernel angular misorientation of electron backscatter diffraction data from the creep-deformed microstructures. It is found that differently oriented grains possess different microstrains. These microstrains vary with creep strain in pure Al, but not in the Al-Mg alloy. It is proposed that this behaviour can explain the power-law breakdown in pure Al and the large creep strain observed in Al-Mg. The present findings further corroborate a description of the creep-induced dislocation structure as a fractal, predicated on previous work.

Strengthening of αMg and long-period stacking ordered phases in a Mg-Zn-Y alloy by hot-extrusion with low extrusion ratio

An as-cast sample and two hot-extruded samples with different extrusion ratios (R) of Mg97Zn1Y2 alloy containing the HCP α matrix (αMg) and the long-period stacking ordered phase (LPSO) of about 25-vol%, were used in tensile deformation in situ neutron diffraction experiments, to elucidate the effects of uniquely different microstructural evolutions in αMg and LPSO with varying the R value to the mechanical properties. αMg behaved as the soft phase and LPSO as the hard phase, and hot-extrusion improved the strength of both. At the R value of 5.0, dynamic recrystallization partly occurred in αMg creating a bimodal microstructure, consisting of a deformed αMg component and a recrystallized αMg component. The yield strength of αMg was significantly improved due to the optimal effects of dislocation density accumulation, texture development in the deformed αMg component and grain refinement in the recrystallized αMg component. With increasing the R value to 12.5, grain growth as well as dynamic recrystallization were promoted in αMg, causing a decrease in the yield strength of αMg, but the elongation was improved due to the presence of weakly textured grains. In contrast, the strength of LPSO increased monotonously with increasing the R value due to the developments of kink bands and texture. The density of kink bands saturated at R=5.0, but the texture of LPSO became stronger monotonously with increasing the R value. At R=12.5, the strength improvement of LPSO compensated for the strength decrease of αMg, and maintained the high ultimate tensile strength of the alloy.