High-energy X-ray Diffraction Data Research Articles

Individual phase constitutive properties of a TRIP-assisted QP980 steel from a combined synchrotron X-ray diffraction and crystal plasticity approach

Microstructure-based constitutive models for multiphase steels require accurate constitutive properties of the individual phases for component forming and performance simulations. We address this requirement with a combined experimental/theoretical methodology which determines the critical resolved shear stresses and hardening parameters of the constituent phases in QP980, a TRIP assisted steel subject to a two-step quenching and partitioning heat treatment. High energy X-Ray diffraction (HEXRD) from a synchrotron source provided the average lattice strains of the ferrite, martensite, and austenite phases from the measured volume during in situ tensile deformation. The HEXRD data was then input to a computationally efficient, elastic-plastic self-consistent (EPSC) crystal plasticity model which estimated the constitutive parameters of different slip systems for the three phases via a trial-and-error approach. The EPSC-estimated parameters are then input to a finite element crystal plasticity (CPFE) model representing the QP980 tensile sample. The predicted lattice strains and global stress versus strain curves are found to be 8% lower that the EPSC model predicted values and from the HEXRD measurements, respectively. This discrepancy, which is attributed to the stiff secant assumption in the EPSC formulation, is resolved with a second step in which CPFE is used to iteratively refine the EPSC-estimated parameters. Remarkably close agreement is obtained between the theoretically-predicted and experimentally derived flow curve for the QP980 material.

High energy X-ray diffraction and IR spectroscopy of Pt/Al2O3 during CO oxidation in a novel catalytic reactor cell

AbstractThe operando methodology dictates not only that catalysts are analysed during reaction while activity and selectivity are monitored by analytical methods, but also that the cell in which the measurement is carried out performs as a catalytic reactor. A cell (Chiarello et al., Rev. Sci. Inst. 85 (2014) 074102) used to conduct spectroscopy and diffraction measurements under operando conditions was tested for CO oxidation on a 2 wt% Pt/Al2O3 catalyst and compared with measurements in a conventional quartz catalytic reactor to demonstrate its suitability to derive kinetic data. High energy X-ray diffraction data were collected during alternate CO and O2 pulses under differential conditions to demonstrate the extent of loss of order of the Pt particles upon exposure to the O2 pulse. The presence of a surface oxide species places the catalyst in a higher activity regime compared to the fully reduced one.

The structure of molten CuCl: Reverse Monte Carlo modeling with high-energy X-ray diffraction data and molecular dynamics of a polarizable ion model.

The results of the structural properties of molten copper chloride are reported from high-energy X-ray diffraction measurements, reverse Monte Carlo modeling method, and molecular dynamics simulations using a polarizable ion model. The simulated X-ray structure factor reproduces all trends observed experimentally, in particular the shoulder at around 1 Å(-1) related to intermediate range ordering, as well as the partial copper-copper correlations from the reverse Monte Carlo modeling, which cannot be reproduced by using a simple rigid ion model. It is shown that the shoulder comes from intermediate range copper-copper correlations caused by the polarized chlorides.

Magnetic susceptibility ofYBa2Cu3O6+xcrystals: Unusual Curie behavior and small contributions from charge density waves

We report measurements of the magnetic susceptibility of twinned single crystals of YBa$_{2}$Cu$_{3}$O$_{6+x}$ from just above their superconducting transition temperatures to 300 K with magnetic fields of up to 5 T applied parallel and perpendicular to the CuO$_2$ planes at 7 values of $x$. Appropriate analysis allows the relatively small, but still important, Curie terms to be separated from other contributions to the susceptibility. Our data support a picture in which the Curie terms arise from oxygen disorder in the Cu-O chains. This agrees with published work on polycrystalline samples where the sample cooling rate was varied, but here we show that the Curie plots flatten out above 200 K. We identify small effects of charge density wave (CDW) instabilities in the temperature ($T$) derivative of the in-plane susceptibility $d\chi_{ab}(T)/dT$ and discuss their $x$-dependence. For $x=$0.67 we make a detailed comparison with published high energy X-ray diffraction data using a minimal model involving Fermi arcs, thereby obtaining values for the CDW energy gap and the Helmholtz free energy in a coherence volume. At 80 and 100 K the latter is comparable with, or smaller than $k_BT$ respectively, highlighting the probable importance of thermal fluctuations. We note that the effect of the Lorentz force on charge carriers in the Fermi arcs could provide a simple mechanism for enhancing the CDWs in high magnetic fields, as suggested by recent experiments.

Size dependence of structural parameters in fcc and hcp Ru nanoparticles, revealed by Rietveld refinement analysis of high-energy X-ray diffraction data.

To reveal the origin of the CO oxidation activity of Ruthenium nanoparticles (Ru NPs), we structurally characterized Ru NPs through Rietveld refinement analysis of high-energy X-ray diffraction data. For hexagonal close-packed (hcp) Ru NPs, the CO oxidation activity decreased with decreasing domain surface area. However, for face-centered cubic (fcc) Ru NPs, the CO oxidation activity became stronger with decreasing domain surface area. In comparing fcc Ru NPs with hcp Ru NPs, we found that the hcp Ru NPs of approximately 2 nm, which had a smaller domain surface area and smaller atomic displacement, showed a higher catalytic activity than that of fcc Ru NPs of the same size. In contrast, fcc Ru NPs larger than 3.5 nm, which had a larger domain surface area, lattice distortion, and larger atomic displacement, exhibited higher catalytic activity than that of hcp Ru NPs of the same size. In addition, the fcc Ru NPs had larger atomic displacements than hcp Ru NPs for diameters ranging from 2.2 to 5.4 nm. Enhancement of the CO oxidation activity in fcc Ru NPs may be caused by an increase in imperfections due to lattice distortions of close-packed planes and static atomic displacements.

Thermal expansion in UO2 determined by high-energy X-ray diffraction

Here we present crystallographic analyses of high-energy X-ray diffraction data on polycrystalline UO2 up to the melting temperature. The Rietveld refinements of our X-ray data are in agreement with previous measurements, but are systematically located around the upper bound of their uncertainty, indicating a slightly steeper trend of thermal expansion compared to established values. This observation is consistent with recent first principles calculations.

High energy X-ray diffraction study of the relationship between the macroscopic mechanical properties and microstructure of irradiated HT-9 steel

Samples harvested from an HT-9 fuel test assembly (ACO-3) irradiated for six years in the Fast Flux Test Facility (FFTF) reaching 2–147 dpa at 382–504 °C were deformed in-situ while collecting high-energy X-ray diffraction data to monitor microstructure evolution. With the initiation of plastic deformation, all samples exhibited a clear load transfer from the ferrite matrix to carbide particulate. This behavior was confirmed by modeling of the control material. The evolution of dislocation density in the material as a result of deformation was characterized through full pattern line profile analysis. The dislocation densities increased substantially after deformation, the level of dislocation evolution observed was highly dependent upon the irradiation temperature of the sample. Differences in both the yield and hardening behavior between samples irradiated at higher and lower temperatures suggest the existence of a transition in tensile behavior at an irradiation temperature near 420 °C dividing regions of distinct damage effects.

Structural dynamics and activity of nanocatalysts inside fuel cells by in operando atomic pair distribution studies.

Here we present the results from a study aimed at clarifying the relationship between the atomic structure and activity of nanocatalysts for chemical reactions driving fuel cells, such as the oxygen reduction reaction (ORR). In particular, using in operando high-energy X-ray diffraction (HE-XRD) we tracked the evolution of the atomic structure and activity of noble metal-transition metal (NM-TM) nanocatalysts for ORR as they function at the cathode of a fully operational proton exchange membrane fuel cell (PEMFC). Experimental HE-XRD data were analysed in terms of atomic pair distribution functions (PDFs) and compared to the current output of the PEMFC, which was also recorded during the experiments. The comparison revealed that under actual operating conditions, NM-TM nanocatalysts can undergo structural changes that differ significantly in both length-scale and dynamics and so can suffer losses in their ORR activity that differ significantly in both character and magnitude. Therefore we argue that strategies for reducing ORR activity losses should implement steps for achieving control not only over the length but also over the time-scale of the structural changes of NM-TM NPs that indeed occur during PEMFC operation. Moreover, we demonstrate how such a control can be achieved and thereby the performance of PEMFCs improved considerably. Last but not least, we argue that the unique capabilities of in operando HE-XRD coupled to atomic PDF analysis to characterize active nanocatalysts inside operating fuel cells both in a time-resolved manner and with atomic level resolution, i.e. in 4D, can serve well the ongoing search for nanocatalysts that deliver more with less platinum.

Sequence-Dependent Structure/Function Relationships of Catalytic Peptide-Enabled Gold Nanoparticles Generated under Ambient Synthetic Conditions.

Peptide-enabled nanoparticle (NP) synthesis routes can create and/or assemble functional nanomaterials under environmentally friendly conditions, with properties dictated by complex interactions at the biotic/abiotic interface. Manipulation of this interface through sequence modification can provide the capability for material properties to be tailored to create enhanced materials for energy, catalysis, and sensing applications. Fully realizing the potential of these materials requires a comprehensive understanding of sequence-dependent structure/function relationships that is presently lacking. In this work, the atomic-scale structures of a series of peptide-capped Au NPs are determined using a combination of atomic pair distribution function analysis of high-energy X-ray diffraction data and advanced molecular dynamics (MD) simulations. The Au NPs produced with different peptide sequences exhibit varying degrees of catalytic activity for the exemplar reaction 4-nitrophenol reduction. The experimentally derived atomic-scale NP configurations reveal sequence-dependent differences in structural order at the NP surface. Replica exchange with solute-tempering MD simulations are then used to predict the morphology of the peptide overlayer on these Au NPs and identify factors determining the structure/catalytic properties relationship. We show that the amount of exposed Au surface, the underlying surface structural disorder, and the interaction strength of the peptide with the Au surface all influence catalytic performance. A simplified computational prediction of catalytic performance is developed that can potentially serve as a screening tool for future studies. Our approach provides a platform for broadening the analysis of catalytic peptide-enabled metallic NP systems, potentially allowing for the development of rational design rules for property enhancement.

Electric-field-induced strain contributions in morphotropic phase boundary composition of (Bi1/2Na1/2)TiO3-BaTiO3 during poling

The microscopic contributions to the electric-field-induced macroscopic strain in a morphotropic 0.93(Bi1/2Na1/2TiO3)−0.07(BaTiO3) with a mixed rhombohedral and tetragonal structure have been quantified using full pattern Rietveld refinement of in situ high-energy x-ray diffraction data. The analysis methodology allows a quantification of all strain mechanisms for each phase in a morphotropic composition and is applicable to use in a wide variety of piezoelectric compositions. It is shown that during the poling of this material 24%, 44%, and 32% of the total macroscopic strain is generated from lattice strain, domain switching, and phase transformation strains, respectively. The results also suggest that the tetragonal phase contributes the most to extrinsic domain switching strain, whereas the lattice strain primarily stems from the rhombohedral phase. The analysis also suggests that almost 32% of the total strain is lost or is a one-time effect due to the irreversible nature of the electric-field-induced phase transformation in the current composition. This information is relevant to on-going compositional development strategies to harness the electric-field-induced phase transformation strain of (Bi1/2Na1/2)TiO3-based lead-free piezoelectric materials for actuator applications.

Topological ordering in liquid UO2

A molecular dynamics model of liquid UO2 that is in good agreement with recent high-energy x-ray diffraction data has been analyzed using the Bhatia–Thornton formalism. A pre-peak appears in the topological structure factor SNN(Q) at Q = 1.85(1)Å−1 which is not present in the more common, element specific Faber–Ziman partial structure factors. A radical Voronoi tessellation of the 3D molecular dynamics model shows the presence of a wide distribution of clusters, consistent with presence of highly mobile oxygen atoms. However, 4-fold Voronoi polyhedra (n4) are found to dominate the structure and the majority of clusters can be described by the distribution n3 ⩽ n4 ⩾ n5. It is argued that an open network of 4-fold Voronoi polyhedra could explain the origin of the pre-peak in SNN(Q) and the topological ordering observed in liquid UO2.

Pressure-induced collapsed-tetragonal phase inSrCo2As2

We present high-energy x-ray diffraction data under applied pressures up to $p=29\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$, neutron diffraction measurements up to $p=1.1\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$, and electrical resistance measurements up to $p=5.9\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$, on ${\mathrm{SrCo}}_{2}{\mathrm{As}}_{2}$. Our x-ray diffraction data demonstrate that there is a first-order transition between the tetragonal (T) and collapsed-tetragonal (cT) phases, with an onset above approximately 6 GPa at $T=7\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. The pressure for the onset of the cT phase and the range of coexistence between the T and cT phases appears to be nearly temperature independent. The compressibility along the $a$ axis is the same for the T and cT phases, whereas, along the $c$ axis, the cT phase is significantly stiffer, which may be due to the formation of an As-As bond in the cT phase. Our resistivity measurements found no evidence of superconductivity in ${\mathrm{SrCo}}_{2}{\mathrm{As}}_{2}$ for $p\ensuremath{\le}5.9$ GPa and $T\ensuremath{\ge}1.8$ K. The resistivity data also show signatures consistent with a pressure-induced phase transition for $p \ensuremath{\gtrsim}5.5$ GPa. Single-crystal neutron diffraction measurements performed up to 1.1 GPa in the T phase found no evidence of stripe-type or A-type antiferromagnetic ordering down to 10 K. Spin-polarized total-energy calculations demonstrate that the cT phase is the stable phase at high pressure with a $\frac{c}{a}$ ratio of 2.54. Furthermore, these calculations indicate that the cT phase of ${\mathrm{SrCo}}_{2}{\mathrm{As}}_{2}$ should manifest either A-type antiferromagnetic or ferromagnetic order.

Novel uses of SiO2 nanolubrication in end milling of medium carbon steel for higher compressive residual stress measured by high-energy X-ray diffraction data

Milling is a machining process that removes any desired material from the surface by using relative motion between a work piece and a rotating cutter where the cutting tool intermittently enters and leaves the work piece. The milling process operates in two modes, namely, conventional (up) mode and climb (down) mode. Both modes are known for their significant effects on surface integrity due to the entering movement of the cutting tool and the formation of the chips during cutting process. Use of flood lubrication can improve the residual stress and surface quality of the component. It controls the temperature in cutting zone, reduces the power required, washes away chips, and reduces friction between chips, tools, and workpieces. Moreover, it has a great effect on the environment too. Minimum quantity lubrication can be used as an alternative of lubrication for clean machining. With an addition of nanoparticles into the minimum quantity lubrication, it is expected to enhance the machining performance that meets the environmental friendly purposes. Residual stresses remain in a solid material in the absence of external loading or thermal gradients, which is sometimes undesirable. The presence of compressive residual stresses is beneficial, while the presence of tensile stresses is detrimental. In order to study the residual stress and its relation with the surface quality (after milling process), the effects of reduced oil consumption in minimum quantity lubrication and the addition of SiO2 nanoparticles in minimum quantity lubrication for clean machining are presented in this research. Results indicate that there is an improvement in residual stresses and surface quality especially during conventional (up) milling under minimum quantity lubrication and minimum quantity lubrication–SiO2 nanolubrication condition.

Inter-molecular correlations in liquid Se2Br2

The structure of molecular liquid Se2Br2 was analyzed by means of reverse Monte Carlo structural modeling, using a calculation based on high-energy x-ray diffraction data. It was found that, between the optical isomers of L and D types, the number of L–D neighboring molecular pairs increases, while that of the L–L and D–D pairs decreases with increasing temperature. From this temperature dependence and from the relaxation mode analysis of quasi-elastic neutron scattering spectra, it is reasonable to assume that the presence of L–D pairs relates to genuine inter-molecular interactions while the L–L and D–D pairs appear due to geometrical packing of the gauche-shaped molecules.

Competitive I2 Sorption by Cu-BTC from Humid Gas Streams

Competitive sorption of molecular iodine gas from a mixed stream containing iodine and water vapor is identified and characterized for the hydrophilic Cu-BTC metal–organic framework. By combining simulation (Grand Canonical Monte Carlo and molecular dynamics simulations) with crystallography (high-energy synchrotron-based powder X-ray diffraction data and pair distribution function analyses), we show that I2 substantially adsorbs, in preference to water vapor, into two principal areas. First, it adsorbs in the smallest cage close to the copper paddle wheel. Second, it adsorbs within the main pore with close interactions with the benzene tricarboxylate organic linker. Analysis suggests that I2 forms an effective hydrophobic barrier to minimize water sorption. The finding is relevant to mixed gas streams in nuclear energy industrial processes and accident remediation. This also represents the highest reported I2 sorption by a metal–organic framework (175 wt % I2 or 3 I/Cu).

Effects of rare-earth co-doping on the local structure of rare-earth phosphate glasses using high and low energy X-ray diffraction

Rare-earth co-doping in inorganic materials has a long-held tradition of facilitating highly desirable optoelectronic properties for their application to the laser industry. This study concentrates specifically on rare-earth phosphate glasses, (R2O3)x(R'2O3)y(P2O5)(1-(x+y)), where (R, R') denotes (Ce, Er) or (La, Nd) co-doping and the total rare-earth composition corresponds to a range between metaphosphate, RP3O9, and ultraphosphate, RP5O14. Thereupon, the effects of rare-earth co-doping on the local structure are assessed at the atomic level. Pair-distribution function analysis of high-energy X-ray diffraction data (Q(max) = 28 Å(-1)) is employed to make this assessment. Results reveal a stark structural invariance to rare-earth co-doping which bears testament to the open-framework and rigid nature of these glasses. A range of desirable attributes of these glasses unfold from this finding; in particular, a structural simplicity that will enable facile molecular engineering of rare-earth phosphate glasses with 'dial-up' lasing properties. When considered together with other factors, this finding also demonstrates additional prospects for these co-doped rare-earth phosphate glasses in nuclear waste storage applications. This study also reveals, for the first time, the ability to distinguish between P-O and P[double bond, length as m-dash]O bonding in these rare-earth phosphate glasses from X-ray diffraction data in a fully quantitative manner. Complementary analysis of high-energy X-ray diffraction data on single rare-earth phosphate glasses of similar rare-earth composition to the co-doped materials is also presented in this context. In a technical sense, all high-energy X-ray diffraction data on these glasses are compared with analogous low-energy diffraction data; their salient differences reveal distinct advantages of high-energy X-ray diffraction data for the study of amorphous materials.

Tracking the structural changes in pure and heteroatom substituted aluminophosphate, AIPO-18, using synchrotron based X-ray diffraction techniques

We report the structural changes that occur during the thermal removal of organic template molecules that occlude the pores of small pore nanoporous zeolitic solids, AlPO-18, SAPO-18, CoAlPO-18, ZnAlPO-18 and CoSAPO-18. The calcination process is a necessary step in the formation of active catalysts. The studies performed using time-resolved High Resolution Powder Diffraction (HRPD) and High Energy X-ray Diffraction (HEXRD) techniques at various temperatures reveal that changes that take place are dependent on the type of heteroatom present in the nanoporous solids. While time-resolved HRPD shows clear changes in lattice parameters during the removal of physisorbed water molecules and subsequent removal of the organic template, HEXRD data show changes in various near neighbour distances in AlPO-18, SAPO-18, CoAlPO-18, CoSAPO-18 and ZnAlPO-18 during the calcination process. In particular HEXRD reveals the presence of water molecules coordinated to Al(III) ions in the as-synthesised materials. Upon removal of the template and water, these solids show contraction in the cell volume at elevated temperatures while first and second neighbour distances remained almost unchanged.

Large enhancements of magnetic anisotropy in oxide-free iron nanoparticles

Magnetic characterization of spherical, oxide-free, bcc iron nanoparticles synthesized with β-diketone surfactants has been performed. The results of this characterization, which included particles with diameters ranging between 2 and 5nm show that the nanoparticles have an average anisotropy of 1.9×106±0.3×106J/m3, which is more than an order of magnitude greater than the magnetocrystalline anisotropy of bulk iron. Despite their unusually large anisotropy, these particles can have saturation magnetizations of up to 210Am2/kg (slightly lower than bulk iron). High-energy X-ray diffraction data indicates that the Fe particles have a distorted bcc lattice, which could, at least in part, explain the magnetic behavior of these nanoparticles. Dipolar coupling between particles, while present, is weak and cannot account for the high anisotropy of these nanoparticles.

Medium range order in Zr-noble metal eutectic liquids

The medium range order (MRO) in containerless-processed Zr-noble metal eutectic liquids has been measured using the Beamline Electrostatic Levitation (BESL) technique. High energy X-ray diffraction data were obtained for equilibrium and supercooled Zr75.5Pd24.5 and Zr80Pt20; Zr77Rh23 and Zr82Ir18; and Zr81Au19 liquids. When Zr is alloyed with 5d transition metals (Ir, Pt, Au) a prominent pre-peak in the X-ray static structure factor appears, indicating the presence of extended order. However, the position of the pre-peak is not consistent with size considerations alone. Given the similarities between the 4d and 5d alloying elements in atomic size and enthalpy of mixing with Zr, extended MRO likely exists in all of the compositions studied.

A two-scale methodology for determining the residual stresses in polycrystalline solids using high energy X-ray diffraction data

This paper presents a new method for ascertaining residual stress fields in engineering components. Diffraction data are employed with a finite element discretization to determine the macroscopic (continuum) residual stress field over the workpiece simultaneously with the crystal-scale distribution of elastic strains at each diffraction measurement point. Stress equilibrium and traction free boundary conditions constrain the solution at the continuum scale. The thousands of lattice strain measurements made at each diffraction volume ensure that the stress solution is consistent with crystal-scale elastic distortions. Finally, integrated over all orientations within each aggregate, the crystal-scale stresses must match the continuum stress. The method was demonstrated using a shrink fit specimen with a nickel-base superalloy disk fit over a stainless steel shaft. High energy synchrotron X-ray diffraction experiments conducted at the Advanced Photon Source, Argonne National Laboratory, provided nearly 1 million lattice strain measurements. Using these data, the new methodology produced a stress field that satisfied the macroscopic constraints and matched the crystal-scale distortions at each diffraction volume as manifest by spherical harmonic expansions of the lattice strain tensor over orientation space. The residual stress distribution exhibits the general features of an axisymmetric analytical approximation, but also contains details that likely arise from the pre-existing material state and fabrication of the shrink fit assembly. Projections of the spherical harmonic expansions of the crystal-scale lattice strain tensor matched the experimental lattice strain pole figures. Issues related to diffraction volume spacing (spatial resolution) and specimen shadowing are also discussed.