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High-resolution, x-ray phase contrast microscopy, a key technique with promising potential in biomedical imaging and diagnostics, is based on narrow-slit high-aspect-ratio gold gratings. We present the development, fabrication details, and experimental testing of the freestanding 10 ÎĽ m thick gold membrane masks with an array of 0.9â€"1.5 ÎĽ m void slit apertures for a novel low-energy x-ray microscope. The overall mask size is 4 mm Ă— 4 mm, with a grating pitch of 7.5 ÎĽ m, 6.0â€"6.6 ÎĽ m wide gold bars are supported by 3 ÎĽ m wide crosslinks at 400 ÎĽ m intervals. The fabrication process is based on gold electroplating into a silicon mold coated with various thin films to form a voltage barrier, plating base, and sacrificial layer, followed by the mold removal to obtain the freestanding gold membrane with void slit apertures. We discuss key aspects for the materials and processes, including gold structures homogeneity, residual stresses, and prevention of collapsing of the grid elements. We further demonstrate the possibility to obtain high-resolution, high contrast 2D images of biological samples using an incoherent, rotating anode x-ray tube. [ABSTRACT FROM AUTHOR]

Framework oxide materials are well-known for exhibiting not only negative thermal expansion (NTE), but also demonstrating thermal expansion that can be controlled using composition as a tuning parameter. In this work, we study the intrinsic thermal expansion properties of Co _2 V _2 O _7 , which has shown bulk linear NTE, and attempt to understand how substituting Ni ^2+ for Co ^2+ will affect the thermal expansion. The isomorphic solid solution is synthesized through solid-state methods and characterized using x-ray diffraction (XRD), diffuse reflectance spectroscopy, and neutron diffraction. The size difference between Ni ^2+ and Co ^2+ as well as the polyhedral volume of each Co ^2+ metal coordination environment in the crystal structure allows Ni ^2+ to partially be directed toward one crystallographic site over the other. Variable temperature synchrotron XRD data are employed to understand intrinsic thermal expansion. Across the solid solution, no intrinsic NTE is observed at the microscopic level, yet a degree of tunability in the thermal expansion coefficient with Ni substitution is demonstrated. The disparities between the intrinsic and bulk thermal expansion properties suggest that a morphological mechanism may have resulted in NTE in the bulk.

The mixed valence Cr ^3+ /Cr ^4+ compound NaCr _2 O _4 , hosts a plethora of unconventional electronic properties. In the present study, muon spin rotation/relaxation ( $\mu^+$ SR) and high-resolution time-of-flight neutron powder diffraction measurements were carried out on high-quality samples to clarify the complex magnetic ground state of this unique material. We identified a commensurate canted antiferromagnetic order (C-AFM) with a canting angle of the Cr spin axial vector equal to $\theta_{\mathrm{c}} = (8.8\pm0.5)^{\circ}$ , and an estimated Cr moment $\mu^{\mathrm{C}}_{\mathrm{Cr}} \sim (4.30\pm0.01)\mu_\mathrm{B}$ . Such an unusually large value of $\mu^{\mathrm{C}}_{\mathrm{Cr}}$ is compatible with the existence of high-spin Cr sites created by the presence of an unconventional negative charge transfer state in NaCr _2 O _4 . In addition to the C-AFM structure, a novel magnetic supercell was also revealed. Such supercell display an incommensurate (IC)-AFM propagation vector (0 0 ${\textstyle \frac{1}{2}-}\delta$ ), having a Cr moment $\mu^{\mathrm{IC}}_{\mathrm{Cr}} = (2.20\pm0.03)\mu_\mathrm{B}$ . It is suggested that the C-AFM and IC-AFM modulations have two different electronic origins, being due to itinerant and localized contributions to the magnetic moment respectively. Finally, the direct measurement of the magnetic order parameter for the C-AFM structure provided a value of the critical exponent $\beta = 0.245 \approx \frac{1}{4}$ , suggesting a non conventional critical behavior for the magnetic phase transition in NaCr _2 O _4 .

Neutron diffraction is a useful technique for mapping residual strains in dense metal objects. The technique works by placing an object in the path of a neutron beam, measuring the diffracted signals and inferring the local lattice strain values from the measurement. In order to map the strains across the entire object, the object is stepped one position at a time in the path of the neutron beam, typically in raster order, and at each position a strain value is estimated. Typical dwell times at neutron diffraction instruments result in an overall measurement that can take several hours to map an object that is several tens of centimeters in each dimension at a resolution of a few millimeters, during which the end users do not have an estimate of the global strain features and are at risk of incomplete information in case of instruments outages. In this paper, we propose an object adaptive sampling strategy to measure the significant points first. We start with a small initial uniform set of measurement points across the object to be mapped, compute the strain in those positions and use a machine learning technique to predict the next position to measure in the object. Specifically, we use a Bayesian optimization based on a Gaussian process regression method to infer the underlying strain field from a sparse set of measurements and predict the next most informative positions to measure based on estimates of the mean and variance in the strain fields estimated from the previously measured points. We demonstrate our real-time measure-infer-predict workflow on additively manufactured steel parts—demonstrating that we can get an accurate strain estimate even with 30%–40% of the typical number of measurements—leading the path to faster strain mapping with useful real-time feedback. We emphasize that the proposed method is general and can be used for fast mapping of other material properties such as phase fractions from time-consuming point-wise neutron measurements.

A lab-made, multilayered Li-ion battery pouch cell is investigated using in-operando neutron powder diffraction (NPD) and spatially resolved powder X-ray diffraction (SR-PXRD) with the aim of investigating how to compare the information obtained from the two complementary techniques on a cell type with a complicated geometry for diffraction. The work focusses on the anode and cathode lithiation as obtained from the LiC6/LiC12 weight ratio and the NMC111 c/a-ratio, respectively. Neutron powder diffractograms of a sufficient quality for Rietveld refinement are measured using a rotation stage to minimize geometrical effects. Using SR-PXRD, the cell is shown to be non-uniform in its anode and cathode lithiation, with the edges of the cell being less lithiated/delithiated than the center in the fully charged state. The non-uniformity is more pronounced for high charging current than low charging current. The averaged SR-PXRD data is found to match the bulk NPD data well. This is encouraging as it seems to allow comparisons between studies using either of these complementary techniques. This work will also serve as a benchmark for our future studies on pouch cells with novel non-commercial cathode and/or anode materials. [ABSTRACT FROM AUTHOR]

We investigate the ultrafast spin dynamics of an antiferromagnet in a ferromagnet/antiferromagnet heterostructure Fe/GdFeO3 via an all-optical method. After laser irradiation, the terahertz spin precession is hard to be excited in a bare GdFeO3 without spin reorientation phase but efficiently in Fe/GdFeO3. Both quasi-ferromagnetic and impurity modes, as well as a phonon mode, are observed. We attribute it to the optical modification of interfacial exchange coupling between Fe and GdFeO3. Moreover, the excitation efficiency of dynamics can be modified significantly via the pump laser influence. Our results elucidate that the interfacial exchange coupling is a feasible stimulation to efficiently excite terahertz spin dynamics in antiferromagnets. It will expand the exploration of terahertz spin dynamics for antiferromagnet-based opto-spintronic devices. [ABSTRACT FROM AUTHOR]

The iron-chalcogenide superconductor FeTe1–xSex displays a variety of exotic features distinct from iron pnictides. Although much effort has been devoted to understanding the interplay between magnetism and superconductivity near x = 0.5, the existence of a spin glass phase with short-range magnetic order in the doping range (x ∼ 0.1–0.3) has rarely been studied. Here, we use DC/AC magnetization and (quasi) elastic neutron scattering to confirm the spin-glass nature of the short-range magnetic order in a Fe1.07Te0.8Se0.2 sample. The AC-frequency dependent spin-freezing temperature Tf generates a frequency sensitivity ΔTf(ω)/[Tf(ω)Δlog10ω] ≈ 0.028 and the description of the critical slowing down with τ = τ0(Tf/TSG – 1)−z v gives TSG ≈ 22 K and zv ≈ 10, comparable to that of a classical spin-glass system. We have also extended the frequency-dependent Tf to the smaller time scale using energy-resolution-dependent neutron diffraction measurements, in which the TN of the short-range magnetic order increases systematically with increasing energy resolution. By removing the excess iron through annealing in oxygen, the spin-freezing behavior disappears, and bulk superconductivity is realized. Thus, the excess Fe is the driving force for the formation of the spin-glass phase detrimental to bulk superconductivity. [ABSTRACT FROM AUTHOR]

The iron-chalcogenide superconductor FeTe1–xSex displays a variety of exotic features distinct from iron pnictides. Although much effort has been devoted to understanding the interplay between magnetism and superconductivity near x = 0.5, the existence of a spin glass phase with short-range magnetic order in the doping range (x ∼ 0.1–0.3) has rarely been studied. Here, we use DC/AC magnetization and (quasi) elastic neutron scattering to confirm the spin-glass nature of the short-range magnetic order in a Fe1.07Te0.8Se0.2 sample. The AC-frequency dependent spin-freezing temperature Tf generates a frequency sensitivity ΔTf(ω)/[Tf(ω)Δlog10ω] ≈ 0.028 and the description of the critical slowing down with τ = τ0(Tf/TSG – 1)−z v gives TSG ≈ 22 K and zv ≈ 10, comparable to that of a classical spin-glass system. We have also extended the frequency-dependent Tf to the smaller time scale using energy-resolution-dependent neutron diffraction measurements, in which the TN of the short-range magnetic order increases systematically with increasing energy resolution. By removing the excess iron through annealing in oxygen, the spin-freezing behavior disappears, and bulk superconductivity is realized. Thus, the excess Fe is the driving force for the formation of the spin-glass phase detrimental to bulk superconductivity. [ABSTRACT FROM AUTHOR]

Two-dimensional van der Waals MnBi2nTe3n+1 (n = 1, 2, 3, 4) compounds have been recently found to be intrinsic magnetic topological insulators rendering quantum anomalous Hall effect and diverse topological states. Here, we summarize and compare the crystal and magnetic structures of this family, and discuss the effects of chemical composition on their magnetism. We found that a considerable fraction of Bi occupies at the Mn sites in MnBi2nTe3n+1 (n = 1, 2, 3, 4) while there is no detectable Mn at the non-magnetic atomic sites within the resolution of neutron diffraction experiments. The occupancy of Mn monotonically decreases with the increase of n. The polarized neutron diffraction on the representative MnBi4Te7 reveals that its magnetization density is exclusively accumulated at the Mn site, in good agreement with the results from the unpolarized neutron diffraction. The defects of Bi at the Mn site naturally explain the continuously reduced saturated magnetic moments from n = 1 to n = 4. The experimentally estimated critical exponents of all the compounds generally suggest a three-dimensional character of magnetism. Our work provides material-specified structural parameters that may be useful for band structure calculations to understand the observed topological surface states and for designing quantum magnetic materials through chemical doping. [ABSTRACT FROM AUTHOR]

Two-dimensional van der Waals MnBi2nTe3n+1 (n = 1, 2, 3, 4) compounds have been recently found to be intrinsic magnetic topological insulators rendering quantum anomalous Hall effect and diverse topological states. Here, we summarize and compare the crystal and magnetic structures of this family, and discuss the effects of chemical composition on their magnetism. We found that a considerable fraction of Bi occupies at the Mn sites in MnBi2nTe3n+1 (n = 1, 2, 3, 4) while there is no detectable Mn at the non-magnetic atomic sites within the resolution of neutron diffraction experiments. The occupancy of Mn monotonically decreases with the increase of n. The polarized neutron diffraction on the representative MnBi4Te7 reveals that its magnetization density is exclusively accumulated at the Mn site, in good agreement with the results from the unpolarized neutron diffraction. The defects of Bi at the Mn site naturally explain the continuously reduced saturated magnetic moments from n = 1 to n = 4. The experimentally estimated critical exponents of all the compounds generally suggest a three-dimensional character of magnetism. Our work provides material-specified structural parameters that may be useful for band structure calculations to understand the observed topological surface states and for designing quantum magnetic materials through chemical doping. [ABSTRACT FROM AUTHOR]

The exchange bias (EB) effects of BiFeO3 (BFO) and Bi0.9La0.1FeO3 nanopowders are investigated. An EB field of 152 Oe and 902 Oe at 60 K are observed for BFO and Bi0.9La0.1FeO3, respectively, when cooled in 20 kOe magnetic field. The enhancement of EB values in the case of Bi0.9La0.1FeO3 is explained based on the combination of Malozemoff's and domain state models. Training effect measurements data fitted with Binek's model suggested that the origin of EB lies in the interaction between the antiferromagnetic (AFM) core and the soft magnetic shell. Memory effect measurements, thermoremanent and isoremanent magnetization studies, and time decay of thermoremanent magnetization studies are done to understand the nature of the shell of both the samples. Time decay of thermoremanent magnetization of BFO is fitted with a stretched exponential based on Kohlrausch–Williams–Watt model, the obtained shape parameter value lies in the range of Heisenberg type spin-glasses. From thermoremanent and isoremanent magnetization plots, a 2D-diluted AFM shell is observed for Bi0.9La0.1FeO3. The field cooling and the temperature dependence of EB are investigated and the results are explained based on the available models of EB. [ABSTRACT FROM AUTHOR]

The effect of Fe and Mn co-doping on the magnetic properties of the antiferromagnetic (AFM) NiO nanoparticles which offer large potential for different magnetic applications have been studied. The Rietveld refinement fitting of powder x-ray diffractometry (XRD) patterns confirmed the phase formation of face-centred cubic crystal structure of NiO and average crystallite size lies in the short range of 32–38 nm. The cavity and broadband ferromagnetic resonance (FMR) measurements taken at room temperature demonstrate the smaller local magnetic inhomogeneity for 4%Mn-4%Fe co-doped NiO nanoparticles as compared to undoped, single doped and co-doped with different concentration NiO nanoparticles. The M-H loops revealed the room temperature ferromagnetism-like behaviour for higher Fe doping concentration and lower Mn doping concentration. This can be attributed to the double exchange interaction. The zero field cooled (ZFC) and field cooled (FC) dc magnetization curves showed a small surface freezing peak (at at low temperatures and a blocking peak (at at higher temperatures. For samples with 4%Mn-4%Fe and 2%Mn-6%Fe, the blocking peak was found at a relatively high temperature in comparison to other samples. This can be attributed to the presence of magnetic exchange interactions which block the magnetic spins against a thermal increase. The ZFC AC-susceptibility showed three peaks; a surface freezing peak at Tf, a blocking peak at TB peak and an anomalous peak at Tx in between and , which was found to be most prominent for the 4%Mn-4%Fe co-doped nanoparticles. The neutron diffraction pattern confirmed the AFM order of the core of the 4%Mn-4%Fe co-doped nanoparticles, which indicates an AFM coupling between the Fe2+ and Mn2+ ions and the Ni2+ ions through super-exchange interaction. Therefore, the origin of TX peak can be attributed to the ferromagnetic coupling between the Fe2+ and Mn2+ ions which has a maximum strength at equal concentration. Thus, small and equal doping concentration of Fe and Mn in NiO nanoparticles increase the magnetic homogeneity which makes them attractive for magnetic applications. [ABSTRACT FROM AUTHOR]

We systematically investigate the magnetic properties of Cu4 – xZnx(OH)6FBr using the neutron diffraction and muon spin rotation and relaxation (μSR) techniques. Neutron-diffraction measurements suggest that the long-range magnetic order and the orthorhombic nuclear structure in the x = 0 sample can persist up to x = 0.23 and 0.43, respectively. The temperature dependence of the zero-field μSR spectra provides two characteristic temperatures, TA0 and Tλ, which are associated with the initial drop close to zero time and the long-time exponential decay of the muon relaxation, respectively. Comparison between TA0 and TM from previously reported magnetic-susceptibility measurements suggest that the former comes from the short-range interlayer-spin clusters that persist up to x = 0.82. On the other hand, the doping level where Tλ becomes zero is about 0.66, which is much higher than threshold of the long-range order, i.e., ∼0.4. Our results suggest that the change in the nuclear structure may alter the spin dynamics of the kagome layers and a gapped quantum-spin-liquid state may exist above x = 0.66 with the perfect kagome planes. [ABSTRACT FROM AUTHOR]

Nanostructuring, structure distortion, and/or disorder are the main manipulation techniques to reduce the lattice thermal conductivity and improve the figure of merit of thermoelectric materials. A single-phase α-MgAgSb sample, MgAg0.97Sb0.99, with high thermoelectric performance in near room temperature region was synthesized through a high-energy ball milling with a hot-pressing method. Here, we report the average grain size of 24–28 nm and the accurate structure distortion, which are characterized by high-resolution neutron diffraction and synchrotron x-ray diffraction with Rietveld refinement data analysis. Both the small grain size and the structure distortion have a contribution to the low lattice thermal conductivity in MgAg0.97Sb0.99. [ABSTRACT FROM AUTHOR]

In this paper, we present an aging study of commercial 18650-type C/LiNi0.33Mn0.33Co0.33O2 lithium-ion cells. The test procedure comprises varying charging currents, discharging currents and resting times between cycles. The cells show a nonlinear capacity fade after a few hundred equivalent full cycles, if cycled with a standard charging and discharging rate of almost 1C, and different resting times. By increasing the discharging current or decreasing the charging current, the lifetime improves and results in a linear capacity fade. The neutron diffraction experiment reveals a loss of lithium inventory as the dominant aging mechanism for both linearlyand nonlinearly-aged cells. Other aging mechanisms such as the structural degradation of anode or cathode active materials, or the deactivation of active materials, cannot be confirmed. With ongoing aging, we observe an increasing capacity loss in the edge area of the electrodes. Whereas the growth of the solid electrolyte interphase defines the early stage, linear aging, marginal lithium deposition is supposed to cause the later stage, nonlinear aging. Capacity recovery caused by lithium stripping and chemical intercalation is shown to be dependent on the cell's state of health. [ABSTRACT FROM AUTHOR]

Thermal batteries are an established primary battery technology and the most commonly used cathodes in these batteries are transition metal disulfides MS2 (whereM= Co, Ni and Fe). However, understanding the evolution of crystalline phases upon battery discharge has been hindered due to the high temperature operation of these batteries. Here we report an experiment that simultaneously collects powder neutron diffraction and electrochemical data as the battery is discharged. Four regions are observed in the diffraction data and four different cobalt containing phases are observed. Multi-phase Rietveld refinement has been used to monitor the evolution of phases during discharge and this is linked to the battery discharge profile. A new discharge mechanism has been proposed which involves hexagonal CoS instead of Co3S4, and the increase in unit cell parameters on discharge suggests the formation of a sulfur deficient solid solution before transformation to Co9S8. This behavior seems reminiscent of that of NiS2 suggesting that the discharge mechanisms of transition metal disulfides may have more similarities than originally thought. [ABSTRACT FROM AUTHOR]

Na0.79CoO2 and Na0.79Co0.7Mn0.3O2 with a layered hexagonal structure (P2-type) were synthesized by the Pechini process followed by heat-treatment at elevated temperatures in order to achieve the crystalline phases. The samples were characterized with X-ray diffraction, neutron diffraction, magnetic measurements and electrochemical charge-discharge cycling. X-ray diffraction confirmed the presence of P2 layered hexagonal structure after heat-treatment at 900°C in air. Neutron diffraction patterns confirm Mn substitution on Co sites without forming pronounced Mn-Co ordering. Cyclic voltammetry showed the oxidation and reduction peaks of Co and Mn, indicating the intercalation and de-intercalation behavior of the Na ions. A discharge capacity of 60 mAh/g was achieved for both compositions, with the Na0.79Co0.70Mn0.3O2 composition showing a more stable discharge capacity up to 60 cycles. [ABSTRACT FROM AUTHOR]

In modern society, architectural and civil engineering structures such as reinforced concrete buildings require high seismic performance to minimize the ‘megarisk’ exposed from urban earthquake hazards. In the reinforced concrete structures, the bond resistance between rebar and concrete is one important parameter for discussing its performance and it has been typically evaluated by measuring the strain distribution along the embedded rebar. Here, we present in-situ strain and stress measurements for the rebar in reinforced concrete using time-of-flight neutron diffraction as a novel alternative technique to typical strain gauges. It was demonstrated in this study that the three-dimensional deformation behavior of the embedded rebar in normal-strength concrete, cured in air, can be accurately measured under pull-out loading using time-of-flight neutron diffraction. Wider applications of neutron diffraction in the structural engineering field are expected for advanced understanding of actual phenomena on reinforced concrete structures. [ABSTRACT FROM AUTHOR]

The thermoelectric and thermodynamic properties of polycrystalline InxCo4Sb12 (0.0 ⩽ x ⩽ 0.26) skutterudites were investigated and analysed between 2 and 800 K by means of electrical resistivity, thermopower, thermal conductivity and specific heat measurements. Hall effect, sound velocity and thermal expansion measurements were also made in order to gain insights into the transport and elastic properties of these compounds. The impact of the In filling on the crystal structure as well as the thermal dynamics of the In atoms were tracked down to 4 K using powder neutron diffraction experiments. Analyses of the transport data were compared with the evolution of the electronic band structure with x determined theoretically within the Korringa–Kohn–Rostoker method with the coherent potential approximation. These calculations indicate that In gives rise to a remarkably large p-like density of states located at the conduction band edge. The electrical properties show typical trends of heavily doped semiconductors regardless of the In content. The thermal transport in CoSb3 is strongly influenced by the presence of In in the voids of the crystal structure resulting in a drop in the lattice thermal conductivity values in the whole temperature range. The low value of the Grüneisen parameter suggests that this decrease mainly originates from enhanced mass-fluctuations and point-defect scattering mechanisms. The highest thermoelectric figure of merit ZT ∼ 1.0 at 750 K was achieved at the maximum In filling fraction, i.e. for x = 0.26. [ABSTRACT FROM AUTHOR]

Previous studies of the size dependent properties of LiFePO4 have focused on the diffusion rate or phase transformation pathways by bulk analysis techniques such as x-ray diffraction (XRD), neutron diffraction and electrochemistry. In this work, in situ Raman spectroscopy was used to study the surface phase change during charge and self-discharge on a more localized scale for three morphologies of LiFePO4: (1) 25 ± 6 nm width nanorods, (2) 225 ± 6 nm width nanorods and (3) ∼2 μm porous microspheres. Both the large nanorod and microsphere geometries showed incomplete delithiation at the end of charge, which was most likely caused by anti-site defects along the 1D diffusion channels in the bulk of the larger particles. Based on the in situ Raman measurements, all of the morphologies studied exhibited self-discharge with time. Among them, the smallest FePO4 particles self-discharged (lithiated) the fastest. While nanostructuring LiFePO4 can offer advantages in terms of lowering anti-site defects within particles, it also creates new problems due to high surface energies that allow self-discharge. The in situ Raman spectroscopy also showed that carbon coating did not provide significant improvement to the stability of the lithiated particles. [ABSTRACT FROM AUTHOR]

The monoclinic double perovskite Sr _2 YRuO _6 has recently gained a renewed interest in order to get a deeper insight into the exotic magnetic ground states associated with geometric frustration. Striking discrepancies between the spin order derived from the neutron diffraction refinements and the macroscopic magnetic and thermal responses is a major challenge that must be addressed. In this work, detailed neutron diffraction measurements as a function of temperature yield a completely different interpretation of the patterns. We show that at low temperatures a spin structure of the K _2 NiF _4 -type is an accessible configuration for the magnetic ground state. In the neighborhood of the magnetic transition, this configuration evolves into a canted superstructure. The deduced temperature dependence of the canting angle exhibits two closely spaced peaks, which are in excellent agreement with the double peaks in the magnetic contribution to the specific heat and in the thermal expansion coefficient. We explain these features in terms of reorientation of the net ferromagnetic moment of the noncollinear spin state, due to the local breaking of the inversion symmetry promoted by the monoclinic distortions, with structural changes acting as the driving force.

A metallic 19th century flute was studied by means of integrated and simultaneous neutron-based techniques: neutron diffraction, neutron radiative capture analysis and neutron radiography. This experiment follows benchmark measurements devoted to assessing the effectiveness of a multitask beamline concept for neutron-based investigation on materials. The aim of this study is to show the potential application of the approach using multiple and integrated neutron-based techniques for musical instruments. Such samples, in the broad scenario of cultural heritage, represent an exciting research field. They may represent an interesting link between different disciplines such as nuclear physics, metallurgy and acoustics. [ABSTRACT FROM AUTHOR]

Combining in-depth neutron diffraction and systematic bulk studies, we discover that the √5 × √5 Fe vacancy order, with its associated block antiferromagnetic order, is the ground state with varying occupancy ratios of the iron 16i and vacancy 4d sites across the phase-diagram of KxFe2-ySe2. The orthorhombic order, with one of the four Fe sites vacant, appears only at intermediate temperatures as a competing phase. The material experiences an insulator to metal crossover when the √5 × √5 order is highly developed. Superconductivity occurs in such a metallic phase. [ABSTRACT FROM AUTHOR]

Combining in-depth neutron diffraction and systematic bulk studies, we discover that the √5 × √5 Fe vacancy order, with its associated block antiferromagnetic order, is the ground state with varying occupancy ratios of the iron 16i and vacancy 4d sites across the phase-diagram of KxFe2-ySe2. The orthorhombic order, with one of the four Fe sites vacant, appears only at intermediate temperatures as a competing phase. The material experiences an insulator to metal crossover when the √5 × √5 order is highly developed. Superconductivity occurs in such a metallic phase. [ABSTRACT FROM AUTHOR]

In situ high-resolution neutron powder diffraction along with electrochemical analysis was applied to study fatigue processes in commercial LiCoO2 (18650-type, 2600 mAh, 3.0-4.2 V) cells. The Rietveld refinement technique was successfully applied for structural characterization of the cell materials as function of fatigue introduced. The capacity loss determined from the electrochemical investigation has been found proportional to the number of cycles, which the cell underwent, and was 21.9% and 12.8% for the cell cycled for 1000 times at 25°C and 50°C, respectively. This capacity fade has a close correlation to the structural changes in cathode and anode materials with the cell fatigue. A change of the lithium occupation and lattice parameters of the LixCoO2 were observed with proceeding battery fatigue. Transformation of the graphitic anode into LiC6 and LiC12 was identified after the batteries were fully charged. Their weight ratio was found to be dependent on the number of executed cycles. It was concluded that loss of the active lithium in both cathode and anode as well as microstructure changes on the anode side are important factors for the battery degradation. A favorable influence of the elevated cycling temperature on the battery performance was observed. [ABSTRACT FROM AUTHOR]

Neutron methods, are powerful tools for non-destructive investigation of batteries. Taking as an example the case study of a Fe/NaC1 based battery, we investigate a discharged and a half-charged battery using spatially resolved neutron tomography and powder diffraction. Both batteries, the discharged and the half-charged, were studied by neutron tomography to identify the inner structure of the cells. The analysis of the neutron diffraction data allowed identification and quantification of the reaction zones as well as the phase distribution across the cross section of the half-charged battery. [ABSTRACT FROM AUTHOR]

Neutron diffraction is a unique technique to study Li-ion batteries because of its high sensitivity toward detecting lithium ions and ability to differentiate between different cations. This information is essential for understanding the subtle structure/property relationships of active electrode materials. In this study, neutron diffraction was utilized to probe the cation disorder in LiNiO2 with and without Al3+ substitution by different synthesis processes. The powder neutron diffraction revealed that a strong oxidizer rather than Al3+-doping greatly reduces Li+ and Ni2+ mixing. The amount of Ni2+ at Li-site is 6% for Li 1-x(Nio.i5Alo.25)1+xO2 synthesized from excess LiOH, while it is only 0.6% for Li1-x(Ni0.75Al0.25)1+xO2 which was synthesized from excess Li202. The reduction of Ni2+ at Li-sites greatly improves electrochemical performance. The substitution of Al3+ stabilizes the hexagonal lattice of Li1-xNi1+x-yAly)O2 even for highly lithium-deficient phases. [ABSTRACT FROM AUTHOR]

We prepared three types of non-Cu RHQ-Nb3Al wire sample with different matrix structures: an all-Ta matrix, a composite matrix of Nb and Ta with a Ta inter-filament, and an all-Nb matrix. Neutron diffraction patterns of the wire samples were measured at room temperature in the J-PARC 'TAKUMI'. To obtain the residual strains of the materials, we estimated the lattice constant a by multi-peak analysis in the wires. A powder sample of each wire was measured, where the powder was considered to be strain free. The grain size of all the powder samples was below 0.02 mm. For the wire sample with the all-Nb matrix, we also obtained the lattice spacing d by a single-peak analysis. The residual strains of the Nb3Al filament were estimated from the two analysis results and were compared. The resulting residual strains obtained from the multi-peak analysis showed a good accuracy with small standard deviation. The multi-peak analysis results for the residual strains of the Nb3Al filaments in the three samples (without Cu plating) were all tensile residual strain in the axial direction, of 0.12%, 0.12%, and 0.05% for the all-Ta matrix, the composite matrix, and the all-Nb matrix, respectively. The difference in the residual strain of the Nb3Al filament between the composite and all-Nb matrix samples indicates that the type of inter-filament material shows a great effect on the residual strain. In this paper, we report the method of measurement, method of analysis, and results for the residual strain in the three types of non-Cu RHQ-Nb3Al wires. [ABSTRACT FROM AUTHOR]

Internal lattice strains under a tensile load for a seven-strand cable consisting of three pre-bent CuNb/Nb3Sn and four stainless steel strands were measured by neutron diffraction at room temperature in order to investigate the improvement of mechanical properties of Nb3Sn strands. Stress-lattice strain curves of Nb3Sn and stainless steel strands were obtained, and the effective stress for a Nb3Sn strand was estimated by considering the load sharing of a stainless strand. It was found that the reinforcement with stainless steel strands is an effective way to reduce an applied electromagnetic tensile load for Nb3Sn strands for superconducting magnet application. [ABSTRACT FROM AUTHOR]

The crystallographic structure and magnetic properties of La(Fe11:4Al1:6)C0:02 are studied by magnetic measurement and powder neutron diffraction with temperature and applied magnetic field. Rietveld refinement shows that La(Fe11:4Al1:6)C0:02 crystallizes into the cubic NaZn13-type with two different Fe sites: FeI (8b) and FeII (96i), and that Al atoms preferentially occupy the FeII site. A ferromagnetic state can be induced at a medial temperature of 39 K-139 K by an external magnetic field of 0.7 T, and a large lattice is correspondingly found at 100 K and 0.7 T. In all other conditions, La(Fe11:4Al1:6)C0:02 has no net magnetization in the paramagnetic (T > TN = 182 K) or antiferromagnetic states, and thus keeps its small lattice. Analysis of the Fe-Fe bond length indicates that the ferromagnetic state prefers longer Fe-Fe distances. [ABSTRACT FROM AUTHOR]

The ENGIN-X beamline is a dedicated engineering science facility at ISIS optimized for the measurement of strain, and thus stress, deep within crystalline materials using the atomic lattice planes as an atomic 'strain gauge'. Internal stresses in materials have a considerable effect on material properties including fatigue resistance, fracture toughness and strength. The growing interest in properties of materials at high temperatures may be attributed to the dynamic development in technologies where materials are exposed to a high-temperature environment for example in the aerospace industry or fission and fusion nuclear reactors. This article describes in detail the design and construction of a furnace for neutron scattering measurements of internal stress in engineering materials under mechanical load and in elevated temperature environments, designed to permit a range of gases to provide a non-oxidizing atmosphere for hot samples. [ABSTRACT FROM AUTHOR]

The compounds, Li1.03Mn1.97O4 and Li1.06Mn1.94O4 were prepared by the polymer precursor method followed by heat treatment at 650°C for 6 hours in air. X-ray and neutron diffraction, scanning electron microscopy, and the Brunauer-Emmett-Teller surface area and density determination techniques were used to characterise the compounds. The lattice parameters obtained using neutron diffraction data of Li1.03Mn1.97O4 and Li1.06Mn1.94O4 are smaller than the parent LiMn2O4 at a = 8.20717(17) and 8.22899(13) Å, respectively. Cyclic voltammetry studies were carried out in the potential range of 3.5-4.4V at scan rate of 0.058 mV/sec. Li-doped LiMn2O4 showed the main cathodic and anodic redox peaks at ~3.9/4.0 and ~4.1/4.15V, respectively. The reversible charge capacities of Li1.03Mn1.97O4 with an applied current rate of 360 mA g-1 at the end of 2nd and 230 th cycle are 88 and 83 (±3) mAh g-1, respectively. At a current rate of 600 mA g-1 these charge capacities are 67 and 61 (±3) mAh g-1, respectively. Li1.06Mn1.94O4 shows a capacity of 64 and 62 (±3) mAh g-1 at the end of 2nd and 100th cycles, respectively, at a current rate of 360 mA g-1. [ABSTRACT FROM AUTHOR]

In this paper, we report an investigation of the ferromagnetic state and the nature of ferromagnetic transition of nanoparticles of La0.67Ca0.33MnO3 using magnetic measurements and neutron diffraction. The investigation was performed on nanoparticles with crystal size down to 15 nm. The neutron data show that even down to a size of 15 nm the nanoparticles show finite spontaneous magnetization (MS) although the value is much reduced compared to the bulk sample. We observed a non-monotonic variation of the ferromagnetic-to-paramagnetic transition temperature TC with size d and found that TC initially enhances upon size reduction, but for d < 50 nm it decreases again. The initial enhancement in TC was related to an increase in the bandwidth that occurred due to a compaction of the Mn-O bond length and a straightening of the Mn-O-Mn bond angle, as determined from the neutron data. The size reduction also changes the nature of the ferromagnetic-to-paramagnetic transition from first order to second order with critical exponents approaching mean field values. This was explained as arising from a truncation of the coherence length by the finite sample size. [ABSTRACT FROM AUTHOR]

In underdoped high-Tc cuprates, d-wave superconductivity competes with antiferromagnetism. It has generally been accepted that suppressing superconductivity leads to the nucleation of spin-density wave (SDW) order with wavevector near (π,π). We show theoretically, for a d-wave superconductor in an applied magnetic field including disorder and electronic correlations, that the creation of SDW order is in fact not simply due to suppression of superconductivity, but rather due to a correlation-induced splitting of an electronic bound state arising from the sign change of the order parameter along quasiparticle trajectories. The induced SDW order is therefore a direct consequence of the d-wave symmetry. The formation of anti-phase domain walls proves to be crucial for explaining the heretofore puzzling temperature dependence of the induced magnetism as measured by neutron diffraction. [ABSTRACT FROM AUTHOR]

In this work the magnetic and superconducting properties of HoNi2B2C were investigated by using powder neutron diffraction and the specific heat and upper critical field (Hc2) measurements as a function of temperature. Below T = 8 K, three distinct anomalies at the temperatures TN = 5.2 K, TH1 = 5.6K and TM = 6.0K were observed in the specific heat of HoNi2B2C, as reported in the literature. Our neutron data confirm the transitions to the Néel structure (qN = c*) at TN and to the modulated structure (qM = 0.586a*) at TM. The peak at TH1 = 5.7K in the specific heat data, whose exact nature was not known hitherto, is now attributed to the onset of a qH1 = 0.905c* magnetic helical structure as seen in our neutron data. Comparison between the thermal evolution of the magnetic structures and the temperature dependence of the upper critical field confirms that the first Hc2(T ) depression at 6.1K arises from the qM = 0.586a* modulated magnetic structure. The second depression in Hc2(T ) below 5.7K can be ascribed to the qH1 = 0.905c* magnetic helical structure. [ABSTRACT FROM AUTHOR]