Neutron Diffraction Analysis Research Articles

Postsynthetic Functionalization of Mg-MOF-74 with Tetraethylenepentamine: Structural Characterization and Enhanced CO2 Adsorption.

Postsynthetic functionalization of magnesium 2,5-dihydroxyterephthalate (Mg-MOF-74) with tetraethylenepentamine (TEPA) resulted in improved CO2 adsorption performance under dry and humid conditions. XPS, elemental analysis, and neutron powder diffraction studies indicated that TEPA was incorporated throughout the MOF particle, although it coordinated preferentially with the unsaturated metal sites located in the immediate proximity to the surface. Neutron and X-ray powder diffraction analyses showed that the MOF structure was preserved after amine incorporation, with slight changes in the lattice parameters. The adsorption capacity of the functionalized amino-Mg-MOF-74 (TEPA-MOF) for CO2 was as high as 26.9 wt % versus 23.4 wt % for the original MOF due to the extra binding sites provided by the multiunit amines. The degree of functionalization with the amines was found to be important in enhancing CO2 adsorption, as the optimal surface coverage improved performance and stability under both pure CO2 and CO2/H2O coadsorption, and with partially saturated surface coverage, optimal CO2 capacity could be achieved under both wet and dry conditions by a synergistic binding of CO2 to the amines as well as metal centers.

Residual stress and diffraction line-broadening analysis of Al2O3/Y-TZP ceramic composites by neutron diffraction measurement

Time-of-flight neutron diffraction and Rietveld analysis have been used to investigate the residual stresses, crystallite structure and microstructural features in Al2O3/Y-TZP ceramic composites fabricated by two different green processing techniques (a novel tape casting and conventional slip casting) and with different zirconia content (5 and 40vol.% Y-TZP). The change in lattice parameters, individual peak shifts and peak-broadening were analyzed, in order to calculate the uniform residual stress field (mean phase stresses and peak-specific stresses) and the non-uniform microstrains. Peak-specific residual stresses were calculated for different hkl reflections both for the Al2O3 matrix and the Y-TZP particulates. The sign and the magnitude of the peak-specific residual stress are highly dependent on the individual hkl reflection studied and on the volume fraction of zirconia. Peak broadening was observed in the Y-TZP reflections, due to non-uniform microstrains. Both the mean phase stress field and the non-uniform microstrains were mainly influenced by the Y-TZP content in the studied Al2O3/Y-TZP composites, irrespective of the measured direction and the fabrication process.

Neutron diffraction analysis of structural transformations in lithium-ion batteries

The possibilities of using neutron diffraction in real-time studies of structural transformations occurring in crystalline functional materials during the action of external factors are discussed. As an example, the diffraction patterns are directly collected with 5-min resolution in the course of three charge–discharge cycles of a commercial lithium-ion battery (operando mode). It is shown that the analysis of spectrum evolution allows the main processes occurring in electrode materials to be characterized, namely, to identify the structural transformations, assess the fraction of material involved in the process, follow the kinetics and the degree of symmetry of charge–discharge processes, compare the structural transformations with the charge–discharge characteristic of the battery. The high-resolution neutron diffraction in combination with X-ray diffraction and X-ray spectral elemental analysis makes it possible to elucidate the structural type and composition of the working electrode and determine its microsctructural characteristics. Neutron diffraction is shown to be a powerful method often sufficient for studying structural transformations in complex multi-component objects.

Comparative study of structural phase transitions in bulk and powdered Fe–27Ga alloy by real-time neutron thermodiffractometry

Phase transformations in an iron–gallium alloy have been analyzed by in situ real-time neutron diffraction in the temperature range from 293 to 1223 K. Two compositionally identical samples were studied: the first was in the as-cast bulk state, and the second was ground into a powdered state. In both samples, the same sequence of structural transitions was recorded on heating with a constant heating rate (D03 → A2 → L12 → D019 → A2), and the same structural state (D03 + L12) was recorded after slow cooling to room temperature. Owing to strong texture in the bulk sample, only diffraction patterns of the powdered sample were treated with the Rietveld method to determine the volume fractions of the coexisting phases, the coefficients of thermal expansion, and the thermal and static atomic disorder parameters. The occupancy of Ga positions and the ordered iron magnetic moment were refined at selected temperatures. The level of microstrain in the crystallites in the initial as-quenched state is small, but it sharply increases in the course of phase transitions when the alloy is heated. The microstrains are high and strongly anisotropic after slow cooling. Generally, phase transformations occur similarly in the powdered and bulk samples, but with a noticeable difference in details. The fulfilled analysis of the bulk and powdered samples allowed the real possibilities of the quantitative neutron diffraction analyses of phase transitions in ferromagnetic ordered alloys to be assessed.

Numerical and experimental investigations on shot-peened high-strength steel by means of hole drilling, X-ray, synchrotron and neutron diffraction analysis

Abstract Numerous experimental works have been devoted to studying the influence of different shot peening parameters on the surface material conditions in different metals in the last decades. Most of the research work has been focused on experimental determination of the residual stress and its depth profile by means of X-ray diffraction and corresponding electro-polishing of the surface layers or byhole drilling method. This state of knowledge has led to the development of phenomenological models to describe the surface material conditions qualitatively. Since there are quite a number of parameters, which could influence the residual stress field after shot peening, covering the whole possible process parameters combinations with the purpose of experimentally determining the residual stress profiles could be difficult. A deeper insight into the residual stress states after shot peening could be possible on the basis of sound physical principles by means of numerical approaches. In this study, shot peening of high strength steel S690QL has been modeled and simulated. The results have been compared with the residual stress depth profiles determined by X-ray, synchrotron, neutron diffraction and hole drilling method.

In-situ neutron diffraction during stress relaxation of a single crystal nickel-base superalloy

The stress relaxation behaviour of a single crystal nickel-base superalloy has been quantified using time-of-flight neutron diffraction analysis for a range of temperatures relevant to casting. A new iterative analysis methodology is described to isolate the lattice strain behaviour of the γ matrix and γ′ precipitate phases from data obtained sufficiently rapidly to help elucidate the microscopic effect of macroscopic stress relaxation. The independent response of γ and γ′ is revealed, showing the temperature sensitivity of lattice strain relaxation. The γ/γ′ response is discussed in the context of thermo-mechanical conditions that may affect the propensity for recrystallisation.

Partitioning of Co2+ and Mn2+ into meridianiite (MgSO4·11H2O): Ternary solubility diagrams at 270 K; cation site distribution determined by single-crystal time-of-flight neutron diffraction and density functional theory

We have grown single crystals of M2+SO4 hydrates at 270 K from aqueous solutions in the ternary systems CoSO4–MgSO4–H2O and MnSO4–MgSO4–H2O. These systems exhibit broad stability fields for a triclinic undecahydrate on the Mg-rich side (i.e., Co- or Mn-bearing meridianiite solid solutions) and stability fields for monoclinic heptahydrates on the Mg-poor side (i.e., Mg-bearing solid solutions of bieberite or mallardite). The solubility curves and distribution coefficients, describing the partitioning of M2+ ions between liquid and solid phases, have been determined by thermo-gravimetric and spectroscopic techniques. A subset of M2+SO4·11H2O specimens were selected for single-crystal time-of-flight neutron diffraction analysis in order to evaluate preferential occupancy of symmetry-inequivalent coordination polyhedra in the structure. Considering the nearly identical dimensions of the first coordination shells, there is a surprising difference in the distribution of Co and Mn over the two available sites.

Quartz preferred orientation in naturally deformed mylonitic rocks (Montalto shear zone–Italy): a comparison of results by different techniques, their advantages and limitations

In the geologic record, the quartz c-axis patterns are widely adopted in the investigation of crystallographic preferred orientations (CPO) of naturally deformed rocks. To this aim, in the present work, four different methods for measuring quartz c-axis orientations in naturally sheared rocks were applied and compared: the classical universal stage technique, the computer-integrated polarization microscopy method (CIP), the time-of-flight (TOF) neutron diffraction analysis , and the electron backscatter diffraction (EBSD). Microstructural analysis and CPO patterns of quartz, together with the ones obtained for feldspars and micas in mylonitic granitoid rocks, have been then considered to solve structural and geological questions related to the Montalto crustal scale shear zone (Calabria, southern Italy). Results obtained by applying the different techniques are discussed, and the advantages as well as limitations of each method are highlighted. Importantly, our findings suggest that patterns obtained by means of different techniques are quite similar. In particular, for such mylonites, a subsimple shear (40% simple shear vs 60% pure shear) by shape analysis of porphyroclasts was inferred. A general tendency of an asymmetric c-maximum near to the Z direction (normal to foliation) suggesting dominant basal slip, consistent with fabric patterns related to dynamically recrystallization under greenschist facies, is recognized. Rhombohedral slip was likely active as documented by pole figures of positive and negative rhombs (TOF), which reveal also potential mechanical Dauphine twinning. Results showed that the most complete CPO characterization on deformed rocks is given by the TOF (from which also other quartz crystallographic axes can be obtained as well as various mineral phases may be investigated). However, this use is restricted by the fact that (a) there are very few TOF facilities around the world and (b) there is loss of any domainal reference, since TOF is a bulk type analysis. EBSD is a widely used technique, which allows an excellent microstructural control of the user covering a good amount of investigated grains. CIP and US are not expensive techniques with respect the other kind of investigations and even if they might be considered obsolete and/or time-consuming, they have the advantage to provide a fine and grain by grain “first round” inspection on the investigated rock fabric.

Neutron diffraction and finite element analysis of the residual stress distribution of copper processed by equal-channel angular pressing

Residual stress remaining after plastic deformation significantly affects the physical and chemical behaviors of materials. In this work, the residual stress distribution in Cu after single-pass equal-channel angular pressing (ECAP) was evaluated using neutron diffraction and the finite element method (FEM). The residual stress distributions simulated using the FEM are in good agreement with the experimental results measured using the neutron diffraction method. The workpiece had non-uniform distribution of residual stresses from bottom to top region of a rod specimen with circular cross-section. The axial residual stress in the top region of the workpiece was highly tensile; while it was only slightly tensile in the bottom region. On the other hand, the radial and hoop residual stresses were tensile in the bottom region, whereas they were compressive in the top region. Despite such non-uniformity of residual stresses, the middle region of the workpiece had relatively homogeneous tensile residual stresses. This investigation on the residual stress distribution in the ECAP-processed material provides a new window from which engineering problems in related with residual stress can be issued and solved.

Empirically testing vaterite structural models using neutron diffraction and thermal analysis.

Otoliths, calcium carbonate (CaCO3) ear bones, are among the most commonly used age and growth structures of fishes. Most fish otoliths are comprised of the most dense CaCO3 polymorph, aragonite. Sturgeon otoliths, in contrast, have been characterized as the rare and structurally enigmatic polymorph, vaterite—a metastable polymorph of CaCO3. Vaterite is an important material ranging from biomedical to personal care applications although its crystal structure is highly debated. We characterized the structure of Lake Sturgeon otoliths using thermal analysis and neutron powder diffraction, which is used non-destructively. We confirmed that while Lake Sturgeon otoliths are primarily composed of vaterite, they also contain the denser CaCO3 polymorph, calcite. For the vaterite fraction, neutron diffraction data provide enhanced discrimination of the carbonate group compared to x-ray diffraction data, owing to the different relative neutron scattering lengths, and thus offer the opportunity to uniquely test the more than one dozen crystal structural models that have been proposed for vaterite. Of those, space group P6522 model, a = 7.1443(4)Å, c = 25.350(4)Å, V = 1121.5(2)Å3 provides the best fit to the neutron powder diffraction data, and allows for a structure refinement using rigid carbonate groups.

Neutron Diffraction Analysis of Light Alloys: A Review

The development and application of low density alloys, such as Al and Mg alloys, has rapidly increased in the automotive sector in recent years. This necessitates advanced characterization techniques to assess the evolution of microstructure and phases during casting and processing. Further, understanding the mechanism of evolution of the defects is important in ensuring their minimization. Neutron diffraction has provided a method to determine the factors that trigger hot tearing in Al and Mg alloys as well as determining factors compromising integrity of powertrain components. In addition, neutron diffraction has been applied to examine the phase evolution during solidification of Al and Mg alloys enabling a better understanding of the effect of inoculants and solute additions on the solidification characteristics, resulting in improved castability. This paper highlights the frontiers of neutron diffraction analysis undertaken by the Centre for Near-Net-Shape Processing of Materials, Ryerson University and the CNL-Canadian Neutron Beam Centre.

Local and average structures of BaTiO3-Bi(Zn1/2Ti1/2)O3

The complex crystallographic structures of (1−x)BaTiO3-xBi(Zn1/2Ti1/2)O3 (BT-xBZT) are examined using high resolution synchrotron X-ray diffraction, neutron diffraction, and neutron pair distribution function (PDF) analyses. The short-range structures are characterized from the PDFs, and a combined analysis of the X-ray and neutron diffraction patterns is used to determine the long-range structures. The results demonstrate that the structure appears different when averaged over different length scales. In all compositions, the local structures determined from the PDFs show local tetragonal distortions (i.e., c/a > 1). However, a box-car fitting analysis of the PDFs reveals variations at different length scales. For 0.80BT-0.20BZT and 0.90BT-0.10BZT, the tetragonal distortions decrease at longer atom-atom distances (e.g., 30 Å vs. 5 Å). When the longest distances are evaluated (r > 40 Å), the lattice parameters approach cubic. Neutron and X-ray diffraction yield further information about the long-range structure. Compositions 0.80BT-0.20BZT and 0.90BT-0.10BZT appear cubic by Bragg diffraction (no peak splitting), consistent with the PDFs at long distances. However, these patterns cannot be adequately fit using a cubic lattice model; modeling their structures with the P4mm space group allows for a better fit to the patterns because the space group allows for c-axis atomic displacements that occur at the local scale. For the compositions 0.92BT-0.08BZT and 0.94BT-0.06BZT, strong tetragonal distortions are observed at the local scale and a less-distorted tetragonal structure is observed at longer length scales. In Rietveld refinements, the latter is modeled using a tetragonal phase. Since the peak overlap in these two-phase compositions limits the ability to model the local-scale structures as tetragonal, it is approximated in the refinements as a cubic phase. Collectively, the results demonstrate that alloying BT with BZT results in increased disorder and disrupts the long-range ferroelectric symmetry present in BT, while the large tetragonal distortion present in BZT persists at the local scale.

Neutron diffraction analysis of the microstructure of dispersion-hardening steels

Neutron diffraction was employed in order to determine microdeformations in samples of stainless austenitic dispersion-hardened steels subjected to the action of high temperatures (to 700°С) during different times (up to 12 h). Experiments were conducted on a high-resolution neutron diffractometer using the timeof- flight method. The analysis performed showed systematic changes in the parameters and microdeformations of the crystal lattice. The high level of the diffractometer resolving power made it possible to reveal some important additional details of the microstructure of dispersion-hardened steels as compared to the results obtained earlier on a diffractometer with monochromatic neutron beam.

Unraveling Crystal Structure and Transport Properties of Fast Ion Conducting SrCo0.9Nb0.1O3−δ

SrCo0.9Nb0.1O3−δ (SCN) has been investigated for oxygen transport membrane and solid oxide fuel cell applications as it is more stable than the state-of-the-art Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) material. Here, the crystal structure and transport properties of SCN were systematically investigated. Combined neutron and high-temperature X-ray powder diffraction analyses over the temperature range of 25–800 °C showed that the crystal structure of SCN belongs to the tetragonal space group P4/mmm with the unit cell ac × ac × 2ac, where ac is the lattice parameter of the cubic perovskite at temperatures <160 °C. The tetragonal (P4/mmm) to cubic (Pm3m) phase transition occurred in SCN with increasing temperature. This phase transition affected the electrical conductivity, whereas the impact on the magnetic susceptibility was not significant. The surface exchange and diffusion coefficients of SCN in the temperature range of 600–850 °C were characterized by electrical conductivity relaxation and oxygen permeation m...

Carbonado revisited: Insights from neutron diffraction, high resolution orientation mapping and numerical simulations

One of the most controversial diamond types is carbonado, as its origin and geological history are still under debate. Here, we investigate selected carbonado samples using neutron diffraction and high resolution orientation mapping in combination with numerical simulations. Neutron diffraction analyses show that fine grained carbonado samples exhibit a distinct lack of crystallographic preferred orientation. Quantitative crystallographic orientation analyses performed on transmission electron microscope (TEM) sections reveal that the 2–10μm grains exhibit locally significant internal deformation. Such features are consistent with crystal plastic deformation of a grain aggregate that initially formed by rapid nucleation, characterized by a high number of nucleation sites and no crystallographic preferred orientation. Crystal plastic deformation resulted in high stress heterogeneities close to grain boundaries, even at low bulk strains, inducing a high degree of lattice distortion without significant grain size reduction and the development of a crystallographic preferred orientation. Observed differences in the character of the grain boundary network and internal deformation structures can be explained by significant post-deformation annealing occurring to variable degrees in the carbonado samples. Differences in intensity of crystal bending and subgrain boundary sharpness can be explained by dislocation annihilation and rearrangement, respectively. During annealing grain energy is reduced resulting in distinct changes to the grain boundary geometry. Grain scale numerical modelling shows that anisotropic grain growth, where grain boundary energy is determined by the orientation of a boundary segment relative to the crystallographic orientation of adjacent grains results in straight boundary segments with abrupt changes in orientation even if the boundary is occurring between two triple junctions forming a “zigzag” pattern. In addition, in diamond anisotropic grain growth results in triple junctions that rarely show 120° angles.Our results support the interpretation that carbonados may have undergone at least 2 or 3 stages of development with rapid nucleation, crystal plastic deformation to low strains and variable degrees of post-deformation annealing. Such a history is commonly observed in Earth's crustal or mantle rocks. Hence, for carbonados it is not necessary to invoke an extraordinary and/or extraterrestrial origin and history.The combination of methods utilized here, promises to help advance our understanding of diamond and diamond aggregates in the future.

Time and Voltage Resolved Investigation of Lithium Plating on Graphite Anodes By Operando Electron Paramagnetic Resonance (EPR) Spectroscopy

Graphite is the standard anode material in Li-ion cells due to its high capacity of 372 mAh g-1, good cycling stability and low price. Lithium ions can reversibly intercalate into the graphite host structure at low potentials of 80 – 120 mV vs. Li/Li+. While the low intercalation potential is favorable in terms of energy density, it can cause lithium plating if cells are charged at high rates or at low temperatures. Lithium metal plating adversely affects the cell life due to the loss of active lithium and electrolyte and also poses a serious safety hazard because of internal short circuiting of the cell. For the development of fast and safe charging protocols, a detailed understanding of the plating mechanism is necessary, as lithium plating is the rate limiting step during the charge of Li-ion cells. Unfortunately, there are no analytical techniques available to directly monitor the occurrence of lithium plating on graphite anodes during cell operation, expect for a recent operando neutron diffraction analysis.[1] In general, lithium plating is only indirectly observed based on specific features in the subsequent discharging profile[2] or on the observation of decreasing Coulombic efficiencies[3]. Both methods are elegant and simple, but also have specific limitations: the former fails to detect electrochemically inactive “dead” lithium, while the latter cannot distinguish whether the missing lithium is present in the metallic state (dead lithium) or in ionic form (SEI components). Additionally, microscopic techniques can yield valuable structural and morphological information regarding lithium metal deposits, but are limited to post-mortem analysis of cycled electrodes. In a previous publication,[4] we showed that operando electron paramagnetic resonance (EPR) spectroscopy can be used for the detection of mossy lithium formation on lithium metal anodes. In the present work we extend this concept and suggest to also use operando EPR spectroscopy for the time/voltage resolved and semi-quantitative detection of lithium metal plating on graphite anodes upon cell charge. The spectro-electrochemical cell design has been adapted to implement a reference electrode for the precise determination of the graphite electrode potential. Firstly, the good homogeneity of the electrochemical processes in the EPR cell design are demonstrated, exploiting the characteristic color change of the graphite electrode as a function of the state of charge. In the next step, lithium plating is forced on a fully lithiated graphite electrode. The upper panel in Figure 1 shows the typical voltage profile for a galvanostatically controlled lithium plating process. The exemplary EPR spectra (Figure 1b), measured at positions as indicated in Figure 1a, show two distinct features which differ in signal width and can therefore be discriminated. The broader signal can be assigned to lithium intercalated in graphit (LiCx) and the very narrow signal to metallic lithium. The nearly linear increase of the lithium metal signal intensity (lower panel in Figure 1a) nicely displays the semi-quantitative nature of the EPR technique. Then, the influence of the charging rate on both the amount and the reversibility of lithium metal plating is investigated. It is found, that the amount of plated lithium increases with the charging rate whereas the reversibility decreases. According to a comparison of the EPR results with the Coulombic inefficiency, the majority of the “missing” lithium is “dead” lithium, i.e., it remains trapped in the graphite anode in its metallic form without electrical contact to the electrode. Lastly, the lithium plating process is also investigated at sub-ambient temperatures and in the presence of electrolyte additives. The results are discussed in the context of designing a fast and safe charging protocol.

Targeting transthyretin amyloidosis: joint neutron and X-ray diffraction analysis of a pathogenic protein

Targeting transthyretin amyloidosis: joint neutron and X-ray diffraction analysis of a pathogenic protein

Real-time observations of lithium battery reactions-operando neutron diffraction analysis during practical operation.

Among the energy storage devices for applications in electric vehicles and stationary uses, lithium batteries typically deliver high performance. However, there is still a missing link between the engineering developments for large-scale batteries and the fundamental science of each battery component. Elucidating reaction mechanisms under practical operation is crucial for future battery technology. Here, we report an operando diffraction technique that uses high-intensity neutrons to detect reactions in non-equilibrium states driven by high-current operation in commercial 18650 cells. The experimental system comprising a time-of-flight diffractometer with automated Rietveld analysis was developed to collect and analyse diffraction data produced by sequential charge and discharge processes. Furthermore, observations under high current drain revealed inhomogeneous reactions, a structural relaxation after discharge, and a shift in the lithium concentration ranges with cycling in the electrode matrix. The technique provides valuable information required for the development of advanced batteries.

Determination of Elemental Ratio in an Atomic Column by Electron Energy Loss Spectroscopy.

Atomic-resolution quantification of the elemental ratio of Fe to Mn at the octahedral and tetrahedral sites in brownmillerite Ca2Fe1.07Mn0.93O5 was determined using electron energy-loss spectroscopy combined with aberration-corrected scanning transmission electron microscopy. The combined techniques revealed that oversampling of the spectral imaging data yielded a spatially resolved area that very nearly reflects atomic resolution (∼1.2 Å radius). The average experimental ratios of Fe to Mn within this region were 17.5:82.5 for the octahedral sites and 81.6:18.4 for the tetrahedral sites. The elemental ratio in an octahedral atomic column was successfully extracted by estimating the mixing of signals from nearest neighbor columns. The results indicated that the ratio of Fe to Mn was 13:87 at the octahedral site, which is in good agreement with the results of neutron diffraction analysis. In addition, the uncertainty of experimental results obtained by using an average 1.2 Å radius was less than 10% at octahedral sites, depending on the sample thickness. In contrast, the experimental error due to dechanneling of incident electrons was larger at the tetrahedral sites. This experimental procedure has wide application for determining the spatially resolved composition ratio of elements in perovskite-like compounds.

Residual stresses evolution in Cu tubes, cold drawn with tilted dies – Neutron diffraction measurements and finite element simulation

The use of cold drawing processes for tubes is a flexible and well-established technology to reduce tube dimensions and improve their surface quality. However, wall thickness deviations over the circumference in the semi-finished goods – eccentricity – and residual stresses can be disadvantageous. Nevertheless, drawing with die tilting is clearly affecting the eccentricity as well as the residual stress development. In this paper the evolution of residual stresses over the wall thickness in cold drawn copper tubes was measured from the as-received state over the condition in the deformation zone with tilted dies and finally to the drawn tubes by means of neutron diffraction analysis at SALSA facility in Institut Laue-Langevin (ILL), Grenoble. A model was developed and the behavior of the residual stresses was simulated using the finite element method (FEM). The information about the evolution was necessary for the model and its verification. With this model – which is taking into account the influence of eccentricity on the residual stress development – the cost intensive neutron diffraction measurements can be reduced strongly. The verified model was used to calculate the residual stresses for standard drawn tubes and compared to tilted ones.