Simultaneous Neutron Diffraction Research Articles

Simultaneous neutron powder diffraction and Raman spectroscopy – an approach of combining two complementary techniques

Abstract Diffraction techniques are well-established methods for crystal structure determination as well as phase identification and quantification. Raman spectroscopy can be a valuable complementary characterization technique, because in contrast to the former it yields also information on amorphous materials and it is a probe for short-range structural effects. The herein presented setup allows for simultaneous neutron diffraction and Raman spectroscopy, shown with a sample of lead sulfate under ambient conditions as a proof of principle. In order to fulfil requirements of both methods, a sapphire single-crystal is used as a sample holder. Practical considerations for successful simultaneous in situ neutron diffraction and Raman spectroscopic measurements are given.

Phase-transformation and precipitation kinetics in vanadium micro-alloyed steels by in-situ, simultaneous neutron diffraction and SANS

In-situ Neutron Diffraction and Small-Angle Neutron Scattering (SANS) are employed for the first time simultaneously in order to reveal the interaction between the austenite to ferrite phase transformation and the precipitation kinetics during isothermal annealing at 650 and at 700 °C in three steels with different vanadium (V) and carbon (C) concentrations. Austenite-to-ferrite phase transformation is observed in all three steels at both temperatures. The phase transformation is completed during a 10 h annealing treatment in all cases. The phase transformation is faster at 650 than at 700 °C for all alloys. Additions of vanadium and carbon to the steel composition cause a retardation of the phase transformation. The effect of each element is explained through its contribution to the Gibbs free energy dissipation. The austenite-to-ferrite phase transformation is found to initiate the vanadium carbide precipitation. Larger and fewer precipitates are detected at 700 than at 650 °C in all three steels, and a larger number density of precipitates is detected in the steel with higher concentrations of vanadium and carbon. After 10 h of annealing, the precipitated phase does not reach the equilibrium fraction as calculated by ThermoCalc. The external magnetic field applied during the experiments, necessary for the SANS measurements, causes a delay in the onset and time evolution of the austenite-to-ferrite phase transformation and consequently on the precipitation kinetics.

Composition-Nanostructure Steered Performance Predictions in Steel Wires.

Neutron scattering in combination with scanning electron and atomic force microscopy were employed to quantitatively resolve elemental composition, nano- through meso- to metallurgical structures and surface characteristics of two commercial stainless steel orthodontic archwires—G&H and Azdent. The obtained bulk composition confirmed that both samples are made of metastable austenitic stainless steel type AISI 304. The neutron technique’s higher detection sensitivity to alloying elements facilitated the quantitative determination of the composition factor (CF), and the pitting resistance equivalent number (PREN) for predicting austenite stability and pitting-corrosion resistance, respectively. Simultaneous neutron diffraction analyses revealed that both samples contained additional martensite phase due to strain-induced martensite transformation. The unexpectedly high martensite content (46.20 vol%) in G&H was caused by combination of lower austenite stability (CF = 17.37, p = .03), excessive cold working and inadequate thermal treatment during material processing. Together, those results assist in revealing alloying recipes and processing history, and relating these with corrosion resistance and mechanical properties. The present methodology has allowed access to unprecedented length-scale (μm to sub-nm) resolution, accessing nano- through meso-scopic properties. It is envisaged that such an approach can be extended to the study and design of other metallic (bio)materials used in medical sciences, dentistry and beyond.

Simultaneous neutron diffraction and microwave dielectric characterisation of ammine materials - a non-destructive, non-contact characterisation tool for determining ammonia content in solids.

We have investigated ammonia adsorption in group two halides (MgI2 and CaBr2) using custom-built apparatus that permits simultaneous neutron diffraction, microwave dielectric characterisation and out-gas mass spectroscopy of solid state materials during ammonia adsorption. Deuterated ammonia was flowed over the sample and the uptake - as measured by mass flow meters, mass spectroscopy and structure - compared with the change in dielectric constant. An excellent correlation between ammonia content and dielectric property was observed and, when linked to diffraction, mass flow and mass spectroscopy data, could be used to determine the amount of ammonia present within the solid. The combination of these techniques could also be used to differentiate physisorbed and metal-coordinated ammonia and explain subtleties in the observed structural transformations.

Simultaneous neutron transmission and diffraction imaging investigations of single crystal nickel-based superalloy turbine blades

The integrity of turbine blades is at the heart of every operating aerospace engine or land-based gas turbine. In the most demanding environments, they are cast as single crystals. Whereas traditional neutron imaging is an excellent tool for the non-destructive testing in search of cracks or residual core material, it is insensitive to variations in crystallographic properties. In this work we show that by simultaneous imaging of the diffracted neutrons, one can also probe variations in crystal orientation. In a matter of seconds, different dendritic growth in two industrial turbine blades could be ascertained.

Simultaneous neutron transmission and diffraction contrast tomography as a non-destructive 3D method for bulk single crystal quality investigations

Traditional neutron tomography allows to reconstruct the attenuation cross section, a measure for the material distribution, at high spatial resolution and non-destructively. However, it does not state anything about the ordering structure of the atoms inside this material. Extending the setup with a second neutron imaging detector, diffracted neutrons from the ordered crystal lattice could be captured. Emerging iterative reconstruction techniques allow reconstructing the local Bragg reflectivity in the sample, a measure for the spatial distribution in crystal quality (orientation, homogeneity of phases). Simultaneous acquisition ensures optimal use of the neutron flux and a direct comparison of different sample properties.

In situ observation of ErD2 formation during D2 loading via neutron diffraction

In an effort to better understand the structural changes occurring during hydrogen loading of erbium target materials, we have performed in situ D2 loading of erbium metal (powder) at temperature (450°C) with simultaneous neutron diffraction analysis. This experiment tracked the conversion of Er metal to the α erbium deuteride (solid-solution) phase and then into the β (fluorite) phase. Complete conversion to ErD2.0 was accomplished at 10 Torr D2 pressure with deuterium fully occupying the tetrahedral sites in the fluorite lattice.

Probing the binding and spatial arrangement of molecular hydrogen in porous hosts via neutron Compton scattering

The adsorption of molecular hydrogen (H2) in the alkali-graphite intercalate KC24 has been studied using simultaneous neutron diffraction and Compton scattering. Neutron Compton scattering data for the (H2)xKC24 system (x = 0-2.5) were measured at T = 1.5 K as a function of the relative orientation between the neutron beam and the intercalate c-axis. Synchronous with the above proton-recoil measurements, high-resolution diffraction patterns were measured in backscattering geometry. From these diffraction measurements, the intrinsic mosaicity of the Papyex-based intercalate was determined to be approximately 15 degrees half-width-at-half-maximum, in good agreement with previous studies [Finkelstein et al., Physica B, 2000, 291, 213]. Hydrogen uptake by the intercalate leads to a distinct and readily detectable broadening of the isotropic Compton profile compared to bulk H2, indicative of an enhanced interaction of the H2 molecule with the surrounding solid-state environment. Total proton-recoil intensities also scale linearly with the amount of adsorbed hydrogen. Taking as our starting point previous experimental and theoretical results, the isotropic widths of the proton momentum distributions can be explained on the basis of three energy scales, namely, intramolecular H-H vibrations, followed by H-H librations and H2 centre-of-mass translations. From the coverage dependence of these neutron data, we also establish an upper bound of approximately 10 meV for intermolecular hydrogen-hydrogen interactions. Finally, we observe a weak anisotropy of the width of the proton momentum distributions. Comparison of these experimental data with first-principles predictions indicates that subtle quantum mechanical effects associated with particle delocalisation and exchange lie at the heart of the observed behaviour. Overall, these results demonstrate the suitability and largely untapped potential of neutron Compton scattering to explore H2 uptake by solid-state hosts.

Accurate Crystal Structure Refinement of La3Ta0.25Zr0.50Ga5.25O14

An accurate X-ray diffraction study of a La3Ta0.25Zr0.50Ga5.25O14 single crystal (a = 8.2574(4) A, c = 5.1465(4) A, sp. gr. P321, Z = 1, R/Rw = 0.62/0.57% for 4144 unique reflections and 91 parameters) has been performed with a simultaneous neutron diffraction analysis. Tantalum, zirconium, and gallium atoms are found to occupy the mixed octahedral position (symmetry 32). Gallium atoms and a few zirconium atoms are in the position on axis 2 in the tetrahedron. The tetrahedral position on axis 3 is completely occupied by gallium atoms, while the large polyhedron on axis 2 is occupied by lanthanum atoms. The high resolution and averaging of the results obtained in two independent X-ray experiments with the same sample provided accu- rate structural data, in particular, on the anharmonicity of thermal atomic vibrations (atomic displacements). The X-ray and neutron diffraction data on the atomic displacements are compared.

Bainitic transformation behavior studied by simultaneous neutron diffraction and dilatometric measurement

Bainitic transformation behavior has firstly been observed using in situ neutron diffraction with an angular dispersive method for a hard bainite steel. The dilatometric measurement was carried out simultaneously with the neutron experiment where changes in (1 1 1) austenite and (1 1 0) ferrite diffraction profiles were monitored during heating, cooling and holding at a transformation temperature. The neutron experiments results agree with dilatometry results. They appear to have found that the austenite peak broadening occurs after the onset of bainitic transformation but not before.

A high temperature cell for simultaneous electrical resistance and neutron diffraction measurements

An in situ cell that allows the electrical resistance of a sample pellet to be measured while performing neutron diffraction experiments has been developed at the ISIS pulsed neutron source. The sample is held between two spring loaded platinum electrodes embedded in a boron nitride clamp assembly with the resistance measured using the four-probe method. An outer quartz glass jacket allows the atmosphere within the sample enclosure to be controlled, and the entire device can be accommodated within a standard ISIS neutron furnace for measurements at temperatures up to 1270 K. The operation of this cell is illustrated using data for the structural, magnetic, and electrical properties of chalcopyrite CuFeS(2) collected over the temperature range of 398-873 K on the Polaris powder diffractometer at ISIS.

Simultaneous thermogravimetric and neutron diffraction characterization of hydrogen stores

Simultaneous thermogravimetric and neutron diffraction characterization of hydrogen stores

Ground state magnetic structure of Ce2Ni3Ge5

Abstract We have carried out neutron diffraction experiments on Ce2Ni3Ge5 single crystal. Ce2Ni3Ge5 orders antiferromagnetically below TN = 5 K and exhibits a successive transition at T* = 4.3 K. We have confirmed that the ground state antiferromagnetic structure is characterized with the propagation vector q = [0 1 0]. We have revealed that this magnetic structure stabilizes only below T* = 4.3 K from the simultaneous neutron diffraction and electrical resistivity measurements, contrary to the previously reported neutron powder diffraction result. From the analysis of magnetic reflection intensities, we suggest that the ground state magnetic structure is a canted AF structure, where the moments orient about 20° tilted from the a-axis in the ab-plane. The obtained AF components are 0.45 μB/Ce along the a-axis and 0.15 μB/Ce along the b-axis. It is suggested that the high temperature phase is characterized with another magnetic phase having a different propagation vector, which is not determined in the present study.

Proton-Containing Yttrium-Doped Barium Cerate: A Simultaneous Structural and Dynamic Study by Neutron Scattering

The structural response to proton incorporation in a yttrium-doped barium cerate (BCY), a perovskite exhibiting high protonic and low oxide ion conductivity, and the proton motion therein are investigated in situ as a function of temperature and surrounding atmosphere (flow of moist or dry air). Undoped barium cerate (BC) is taken as a nonproton-conducting reference. Using simultaneous neutron diffraction and quasielastic neutron scattering measurements, we determine and correlate the phase transitions in the BCY lattice, the hydrogen content, and the relative mean square displacement (MSD) of hydrogen atoms over the temperature range of 150-900 C. Presence of OH groups in the BCY system affects the temperature of the high-temperature rhombohedral-cubic phase transition. Uptake of hydrogen occurs from room temperature up to 500-600 C, beyond which the system dehydrates. Onset of dehydration is observed before the rhombohedral-cubic phase transition at 700 C. The relative MSD follows the trend of hydrogen content, peaking also at 500-600 C. Decrease in MSD over a large range of temperatures (500-800 C) suggests a corresponding significant variation of the bonding strengths between the hydrogen atoms and the lattice.

Development of an in situ neutron-scattering facility for research and education in the mechanical behavior of materials

The present work is to establish a suite of instruments for studying the mechanical behavior of advanced materials using in situ neutron-scattering at the impending Spallation Neutron Source (SNS, The Oak Ridge National Laboratory), which will provide the most intense pulsed-neutron source in the world. The state-of-the-art in situ and real-time characterization instrumentation will be developed for VULCAN at SNS. The VULCAN diffractometer is designed to conduct fundamental studies in materials science and engineering with a focus on the mechanical behavior. The instrumentation described here will enable VULCAN to fulfill its full potential. The characterization capabilities to be developed will far surpass anything else available in the world. The simultaneous neutron diffraction and small-angle neutron-scattering (SANS) during mechanical testing will have a tremendous impact on the fundamental understanding of the mechanical behavior of materials. The successful development of the present instrumentation will give materials scientists many new and valuable capabilities for the fundamental study of advanced materials with complex multi-phase/-scale microstructures and various sizes/types (1) under large static/dynamic mechanical loads (including tension, compression, and torsion, i.e., real-world conditions), (2) at high temperatures, and/or (3) under chemical environments. Moreover, such capabilities will allow engineers to probe the behavior of materials and components under realistic operating and processing conditions.

Nuclear ordering and excitations in [formula omitted

The energy splitting of Nd nuclear levels and Nd nuclear polarization in NdFeO 3 have been studied by using high resolution inelastic neutron backscattering with simultaneous neutron diffraction at temperatures between 100 mK and 15 K. Inelastic peaks are observed below 4.5 K with a corresponding energy splitting Δ E = 1.24 μ eV below 0.9 K. The Nd nuclear magnetic moments are polarized below 1 K with a maximal polarization of 17% observed at 100 mK. Both these phenomena directly observed in NdFeO 3 are described by assuming a magnetic hyperfine coupling model. It is found that the present experimental data on NdFeO 3 and the literature data concerning Nd 2 CuO 4 can be consistently described by using the same value of the magnetic hyperfine coupling constant A = 1.10 ( 5 ) μ eV / μ B .

Neutron diffraction study of the contribution of grain contacts to nonlinear stress‐strain behavior

Repeatable, hysteretic loops in quasi‐static loading measurements on rocks are well known; the fundamental processes responsible for them are not. The grain contact region is usually treated as the site of these processes, but there is little supporting experimental evidence. We have performed simultaneous neutron diffraction and quasi‐static loading experiments on a selection of rocks to experimentally isolate the response of these contact regions. Neutron diffraction measures strain in the lattice planes of the bulk of the grain material, so differences between this strain and the macroscopic response yield information about grain contact behavior. We find the lattice responds linearly to stress in all cases, oblivious to the macroscopic unrecoverable strains, curvature, and hysteresis, localizing these effects to the contacts. Neutron diffraction shows that the more granular rocks appear to distribute stresses so that the same strain appears in all the grains, independent of crystallographic orientation.

Anin situneutron diffraction mechanical study of superelastic NiTi and NiTi-TiC composites

Superelastic NiTi and NiTi-TiC composites were subjected to static uniaxial compressive loading while neutron diffraction spectra were simultaneously acquired. A methodology was established to obtain quantitative strain, texture and phase volume fraction information during the forward and reverse stress-induced martensitic transformation. Despite the presence of 10 vol.% of stiff TiC particles, a macroscopic compressive strain of 3% was obtained in the composite on loading and was fully recovered on unloading. The observed behavior suggests that the martensite accommodates the mismatch with the transforming austenite (while they co-exist) and the TiC particles (in the case of the composite). Superelastic NiTi was also subjected to simultaneous neutron diffraction and uniaxial compressive cycling. The average phase strain in the mechanically-loaded austenite (at a given stress) remained unaltered during the load-unload cycles. However, differences in both volume fraction and texture of austenite and martensite were noted as cycling progressed, suggesting that these factors are responsible for the changes in the macroscopic stress-strain response of NiTi with mechanical cycling.

Neutron Scattering Study of Sodium Ammonium Sulphate Dihydrate

A simultaneous neutron diffraction and neutron inelastic scattering experiment on sodium ammonium sulphate dihydrate has been carried out in the temperature range 300 to 20 K. The neutron powder diffraction (NPD) spectra correlate with those found previously using X-ray diffraction dilatometry. The IINS spectra are reported for the first time. For the temperature range from 160 to 200 K, they indicate the existence of a glassy transition or an instability caused by soft optic modes. The generalized phonon density of states G(ω) is also discussed. The observed bands are ascribed to particular vibrational modes of the crystal as a whole and of NH4+, SO42— and H2O groups.

Texture, strain, and phase-fraction measurements during mechanical cycling in superelastic NiTi

Superelastic NiTi was subjected to simultaneous neutron diffraction and uniaxial compressive cycling between 10 and 980 MPa. The objective was an in-situ investigation of the evolution of the stress-induced, reversible transformation between austenite and martensite, to determine the cause of the changes in the macroscopic stress-strain response with cycling. Rietveld refinement was used to analyze the neutron spectra and quantify the phase fraction, texture, and elastic strain. The average phase strain in the mechanically loaded austenite (at a given stress) remained unaltered during the 100 load-unload cycles. However, differences in both the volume fraction and texture of austenite and martensite were noted as cycling progressed, suggesting that these factors are responsible for the changes in the macroscopic stress-strain response of NiTi with mechanical cycling.