Synchrotron-based X-ray Diffraction Research Articles

Studies of intergranular and intragranular stresses in cold-rolled CuNiSi alloys

Applying cold rolling after solution treatment and before aging has been approved to be effective in increasing the strength and electrical conductivity in the Cu–Ni–Si alloys. The present work aims at identifying the evolution of the microstructures and stress states in the aging process of the cold-rolled Cu-2.29 wt%Ni-0.49 wt%Si (Cu-2.29Ni-0.49Si) by means of advanced electron microscopy analysis techniques (SEM-EBSD and TEM) and synchrotron-based high-energy x-ray diffraction techniques (ex-situ and in-situ tension test). Deep attention is paid on the evolution of intergranular and intragranular stresses during aging. A large grain-orientation-dependent intergranular stress is observed in the cold-rolled alloys, which is reduced as extending the aging time. Meanwhile, the intragranular stress is also detected, which keeps stable in the aging process. At last, the individual contributions to the overall electrical resistivity in the aging process are discussed.

In situ neutron diffraction study of a new type of stress-induced confined martensitic transformation in Fe22Co20Ni19Cr20Mn12Al7 high-entropy alloy

We successfully prepared an Fe22Co20Ni19Cr20Mn12Al7 alloy consisting of a face-center cubic (fcc) phase and body-center cubic (bcc) phase that exhibits an outstanding combination of true strength of 1430 MPa and ductility of 19.9% at room temperature (RT). The micromechanical behavior at RT and 77 K for the studied alloy during tensile deformation was investigated using in situ time-of-flight (TOF) neutron diffraction in combination with synchrotron-based high-energy X-ray diffraction (HE-XRD). Here, the striking finding of a large elastic strain of 7.0% and 5.6% is reported for the {200} bcc crystal plane, which was achieved at RT and 77 K, respectively. Such a large lattice distortion observed in the bcc phase was attributed to a new type of stress-induced confined martensitic transformation. We attributed the physical origin of this specific martensitic transformation to the intrinsic microstructural feature of a nano-scale continuous distribution of an ordered-to-disordered crystal structure within the bcc phase, i.e., the disordered A2-structure was distributed continuously in the ordered B2-structure matrix. The stress-induced martensitic transformation from the metastable nano-sized disordered A2-phase was confined by the stable B2-ordered matrix. The new findings in this study provide additional understanding of the deformation mechanisms of high-entropy alloys and insights into alloy design for further enhancement of the mechanical properties of high-performance structural materials used at cryogenic temperatures.

Enhanced Immobilization of Arsenic from Acid Mine Drainage by Detrital Clay Minerals

Arsenic (As) is a potent carcinogen and the most common metal(loid) contaminant in drinking water sources globally. In acidic, Fe-rich systems, nanocrystalline Fe(III) precipitates (Fe(III)NP) are the main scavengers of As. However, the redox cycling of Fe(III)NP highly enhances As mobility and bioavailability. Notably, the irreversible release of As in runoff resulting from reductive dissolution of Fe(III)NP makes the effective remediation of As an ongoing environmental challenge. Here, we show for the first time that detrital clay minerals originating from the partial weathering of coal mining waste substantially increased total As uptake by acid mine drainage (AMD) sediments. The As immobilization mechanisms by the AMD sediments were investigated by the combined use of microbial community structure characterization (16S rRNA), chemical extractions, and synchrotron-based X-ray fluorescence (XRF), diffraction (XRD), and absorption (XANES). The use of an X-ray spot size as small as one micrometer allowed a detailed examination of the heterogeneous AMD sediments. Our results suggest that during sustained redox cycling of iron in Fe(III)NP-clay mixed-mineral systems, the clays controlled As mobility by (1) enhancing heterogeneous precipitation of Fe(III)NP under oxic conditions, which then adsorbed or incorporated As; and (2) facilitating the transfer of As from Fe(III)NP to clay during microbially mediated reduction of Fe(III)NP coatings under anoxic conditions. Designing remediation strategies that incorporate clay could become a promising low-cost strategy for As remediation in mining-impacted areas.

Experimental and theoretical study on elastic properties of crystalline alkali silicate hydrate

Mechanical properties of synthesized sodium silicate mineral, Na-kanemite, was investigated by synchrotron-based high-pressure x-ray diffraction experiment and first-principles calculations. Under hydrostatic pressure, the 020 interlayer peak was substantially diffused while a new 011 peak formed at 0.4 GPa due to the reduction of Pbcn symmetry. Upon unloading, the diffused interlayer peak reappeared to its original position with a less peak intensity and the newly formed peak disappeared. This temporal but reversible phase instability related to the symmetry reduction, can be induced from the vibration effect of water molecules contained in interlayer region that can more significantly affect the structural response of crystals with poor crystallinity and stacking disorder. There is a good agreement of pressure response between experimental data and calculations using GGA functional. In addition, conducted analysis on bond variation revealed that contraction of thickness and distortion of Na layer under pressure which caused partial charge redistribution. Suggested elastic properties and charge data will be used to develop reliable force-field database for further molecular dynamics simulation and diagnose macroscopic impact from alkali-silicate reaction damaged structure.

Effect of stoichiometry on the evolution of thermally annealed long-range ordering in Ni–Cr alloys

Ni-based alloys, such as alloys 690 and 625, are widely used in the nuclear industry as structural components, because of their desirable mechanical properties and resistance to stress corrosion cracking. However, in some high chromium alloys, a disorder-order phase transformation near 33 at% Cr, is known to decrease ductility and fracture toughness. In this study, the ordering transformation is investigated in Ni–Cr binary model alloys to better understand the effects of composition. Model alloys with different stoichiometries (Ni/Cr = 1.8, 2.0, 2.2, 2.4) were isothermally aged up to 10,000 h at three temperatures (373 °C, 418 °C, and 475 °C) and characterized by transmission electron microscopy (TEM), microhardness, and synchrotron-based X-ray diffraction (XRD). TEM results show the evolution of the Ni2Cr (MoPt2-type) ordered precipitates between 3000 h and 10,000 h with corresponding size of ∼10–20 nm. Microhardness testing results show that off-stoichiometry (Ni/Cr ≠ 2.0) alloys exhibit a smaller change with ordering compared to the stoichiometric (Ni/Cr = 2.0) alloy at all temperatures. XRD quantifies ordering induced lattice contraction in the matrix structure and the size of the ordered precipitates. No BCC Cr was detected by XRD or TEM during characterization in the range of 29.83–35.66 at% Cr after 10,000 h of aging, confirming that all of the hardening can be attributed to the development of Ni2Cr in alloys ranging from Ni/Cr of 1.8 to Ni/Cr of 2.4.

A study of the strain distribution by scanning X-ray diffraction on GaP/Si for III–V monolithic integration on silicon

A synchrotron-based scanning X-ray diffraction study on a GaP/Si pseudo-substrate is reported, within the context of the monolithic integration of photonics on silicon. Two-dimensional real-space mappings of local lattice tilt and in-plane strain from the scattering spot distributions are measured on a 200 nm partially relaxed GaP layer grown epitaxially on an Si(001) substrate, using an advanced sub-micrometre X-ray diffraction microscopy technique (K-Map). Cross-hatch-like patterns are observed in both the local tilt mappings and the in-plane strain mappings. The origin of the in-plane local strain variation is proposed to be a result of misfit dislocations, according to a comparison between in-plane strain mappings and transmission electron microscopy observations. Finally, the relationship between the in-plane strain and the free surface roughness is also discussed using a statistical method.

Emergence of the Vortex State in Confined Ferroelectric Heterostructures.

The manipulation of charge and lattice degrees of freedom in atomically precise, low-dimensional ferroelectric superlattices can lead to exotic polar structures, such as a vortex state. The role of interfaces in the evolution of the vortex state in these superlattices (and the associated electrostatic and elastic boundary conditions they produce) has remained unclear. Here, the toroidal state, arranged in arrays of alternating clockwise/counterclockwise polar vortices, in a confined SrTiO3 /PbTiO3 /SrTiO3 trilayer is investigated. By utilizing a combination of transmission electron microscopy, synchrotron-based X-ray diffraction, and phase-field modeling, the phase transition as a function of layer thickness (number of unit cells) demonstrates how the vortex state emerges from the ferroelectric state by varying the thickness of the confined PbTiO3 layer. Intriguingly, the vortex state arises at head-to-head domain boundaries in ferroelectric a1 /a2 twin structures. In turn, by varying the total number of PbTiO3 layers (moving from trilayer to superlattices), it is possible to manipulate the long-range interactions among multiple confined PbTiO3 layers to stabilize the vortex state. This work provides a new understanding of how the different energies work together to produce this exciting new state of matter and can contribute to the design of novel states and potential memory applications.

Copper(I)-Based Highly Emissive All-Inorganic Rare-Earth Halide Clusters

Summary The development of new environmentally friendly luminescent materials is crucial for future solid-state lighting, sensor, and display applications. Here, a Cu(I)-based all-inorganic rare-earth halide material, Rb 8 CuSc 3 Cl 18 , has been synthesized by a solid-state reaction method. In this compound, two Cu(I) ions are connected to three rare-earth halide octahedra to form a paddle-wheel-like cluster. The Cu(I) coordinated rare-earth halide clusters contribute to a strong blue photoluminescence emission. This Cu(I)-regulated emission can be extended to other isostructural compounds, such as Rb 8 CuY 3 Cl 18 . Moreover, the crucial role of Cu(I) has been illustrated by the isostructural non-emissive Rb 8 AgSc 3 Cl 18 . On the basis of comprehensive spectroscopy studies and density functional theory calculations, we found that Cu(I) photo-oxidation and correct orbital-energy-level alignment are crucial for the observed bright-blue emission through a proposed metal (Cu)-to-octahedra ([ScCl 6 ] 3− ) charge-transfer mechanism. The discovery of Cu(I)-based all-inorganic rare-earth halide clusters establishes a new strategy for constructing promising emissive halide materials.

Phase stability and electronic structure of iridium metal at the megabar range

The 5d transition metals have attracted specific interest for high-pressure studies due to their extraordinary stability and intriguing electronic properties. In particular, iridium metal has been proposed to exhibit a recently discovered pressure-induced electronic transition, the so-called core-level crossing transition at the lowest pressure among all the 5d transition metals. Here, we report an experimental structural characterization of iridium by x-ray probes sensitive to both long- and short-range order in matter. Synchrotron-based powder x-ray diffraction results highlight a large stability range (up to 1.4 Mbar) of the low-pressure phase. The compressibility behaviour was characterized by an accurate determination of the pressure-volume equation of state, with a bulk modulus of 339(3) GPa and its derivative of 5.3(1). X-ray absorption spectroscopy, which probes the local structure and the empty density of electronic states above the Fermi level, was also utilized. The remarkable agreement observed between experimental and calculated spectra validates the reliability of theoretical predictions of the pressure dependence of the electronic structure of iridium in the studied interval of compressions.

Structural, magnetic and dielectric properties of vanadium substituted four layered Aurivillius Bi5FeTi3O15 ceramics

Abstract The present work reports the study of four layer Aurivillius compound Bi 5 FeTi 3 O 15 (BFTO) with V 5+ (≤50%) doping at B-site ( F e 3 + , T i 3 + ). This is considered to be equivalent of increasing the magnetic ion ( F e 3 + ) concentration from 25% to 37.5%. Phase purity of the samples is confirmed with lab and synchrotron based x-ray diffraction measurements. The temperature dependent magnetization measurements indicate the paramagnetic nature of BFTO down to 2 K and the development of long-range antiferromagnetic (AFM) ordering with V 5+ doping. It is observed that the AFM Neel transition temperature ( T N ) decreases with increase of V 5+ doping. The presence of iron oxide impurity phases is excluded from the 57 Fe Mossbauer spectroscopy measurements. Temperature dependent dielectric constant measurements show the relaxation behaviour in highly doped samples.

Correlation of Optical, Structural, and Compositional Properties with V-Pit Distribution in InGaN/GaN Multiquantum Wells.

InGaN/GaN double heterostructures and multiquantum wells (MQWs) have been successfully developed since more than 20 years for LED lightning applications. Recent developments show that state-of-the-art LEDs benefit from artificially generated V-pit defects. However, the control of structural and chemical properties plays a tremendous role. In this paper, we report on the lateral distribution of V-pit defects and photoluminescence of InGaN/GaN MQWs grown on thick GaN on patterned sapphire substrates. The synchrotron-based scanning X-ray diffraction microscopy technique K-map was employed to locally correlate these properties with the local tilt, strain, and composition of the InGaN/GaN MQW. Compositional fluctuation is the main factor for the variation of photoluminescence intensity and broadening. In turn, V-pit defects align along small-angle grain boundaries and their strain fields are identified as a reason for promoting the InGaN segregation process on a microscale.

Quantitative analysis of lattice plane microstructure in the growth direction of a modified Na-flux GaN crystal using nanobeam X-ray diffraction

We quantitatively evaluated lattice plane microstructure, which includes lattice plane tilt, spacing, twist, and their fluctuations, in a modified Na-flux GaN bulk single crystal using the synchrotron-based nanobeam X-ray diffraction method. The GaN crystal was fabricated by two-step growth; the first layer had coalescence boundaries as a consequence of faceted growth from the multipoint-seed GaN template, and the second layer grew on the first without faceted growth. Position-dependent ω-2θ-φ mapping analysis revealed in-plane distribution of local lattice plane microstructure along with dislocation morphology around the coalescence boundary and the growth-stage boundary (GSB). Faceted growth from the multipoint seed template led to concentration of a-type dislocations at the coalescence boundary. These dislocations would glide widely on basal planes above the GSB, and then homogeneously propagate toward the surface. As a result, the modified Na-flux GaN crystal had a homogeneous lattice plane microstructure with little bunching of threading dislocations.

The effects of swift Xe ion bombardment on the amorphous structure of a VITROPERM type alloy

Influence of swift Xe ion irradiation (ion energy of 11.1 MeV/u, ion fluences from 2.5 × 1012 to 1.0 × 1013 ions/cm2) on the local structural arrangement of a VITROPERM alloy is investigated using synchrotron-based X-ray diffraction, Fe and Nb K-edge X-ray absorption spectroscopy, and 57Fe Mössbauer spectroscopy techniques. The obtained data show an increase of structural disordering due to ion bombardment. However, no alterations in pairwise interatomic lengths are observed. The irradiation-induced structural modifications can be removed by an appropriate post-irradiation heat treatment. We suggest that the microscopic origin of changes induced by the swift heavy ions could be similar to the structural modifications caused by severe plastic deformation.

Structural behavior of a stuffed derivative of α-quartz, Mg0.5AlSiO4, at high temperature: an in situ synchrotron XRD study

High-temperature structural behavior of a stuffed derivative of α-quartz, Mg0.5AlSiO4, has been investigated using in situ synchrotron-based angle-dispersive powder X-ray diffraction (XRD) from 299 to 1273 K. Rietveld analysis of the XRD data indicates that the framework of Mg0.5AlSiO4 remains isostructural with α-quartz throughout the temperature range tested. As in α-quartz, unit-cell parameters a and c and cell volume V of Mg0.5AlSiO4 increase with increasing temperature, primarily due to progressive tilting of [(Al,Si)O4] tetrahedra along the a axes. However, the rates of increase in the cell parameters and the rate of decrease in the tetrahedral tilt angle (δ) are much smaller for Mg0.5AlSiO4 than for α-quartz. This behavior can be attributed to the occupancy of Mg2+ over the octahedral channel sites in the α-quartz-type framework, effectively hindering the [(Al,Si)O4] tetrahedral tilting. As a result, the α- to β-quartz phase transformation, which exists in silica at 846 K, does not occur in Mg0.5AlSiO4 up to 1273 K, and probably beyond, to its melting point.

Effect of transition metal substitution on structural and dielectric properties of Mg0.5Zn0.5−xCrxCo2O4 (0.0 ≤ x ≤ 0.5) cobaltite

We report the impact of Cr ion doping on structural and dielectric properties of Mg0.5Zn0.5−xCrxCo2O4 (0.0 ≤ x ≤ 0.5). All the samples were prepared by high-temperature solid-state reaction route. X-ray diffraction patterns reveal that Mg0.5Zn0.5−xCrxCo2O4 (0.0 ≤ x ≤ 0.5) crystallizes into more than one phase. Rietveld analysis of Synchrotron-based X-ray diffraction also confirms the existence of secondary phases corresponding to the cubic structure with Fd-3m and Fm3m space group. Scanning electron microscopy (SEM) images confirm the growth in grain size as a result of high sintering temperature. The FTIR spectra of doped cobaltites show two strong peaks at ~ 665 and 563 cm− 1 due to the presence of metal–oxygen bond. Variation in the dielectric constant and dielectric loss with frequency have also been investigated. Both decreases with increasing frequency of the applied alternating field and becomes constant at high frequencies that signify the substantial role of interfacial polarisation. It is also noted that the material having the smallest crystallite size (~ 29.16 nm) has high dielectric constant (~ 1.07 × 105) value. Cole–Cole plot indicates that all the samples of cobaltite show dominant grain capacitance.

Effect of Tensile Strength on the Microstructure of Graphite Impregnated with Salt Revealed by In Situ Synchrotron-Based Two-Dimensional X-ray Diffraction

Owing to the inhomogeneous distribution of FLiNaK salt impregnated into graphite which is observed by scanning electron microscopy and an element probe micro-analyzer, a map scan of in situ real-time tensile synchrotron-based two-dimensional X-ray diffraction (2D-XRD) at several fixed external forces was implemented to reveal the local microstructure evolution of graphite and FLiNaK salt. Notably, a stress concentration area (SCA), that is, the main interaction area between graphite and salt, was found and then transformed from one region to another region because of the unbalanced squeeze interaction between graphite and FLiNaK salt with the increase of external force. During the external stress load process, a smaller grain size, poorer crystallinity of graphite and a larger grain size, better crystallinity of FLiNaK salt appear in the SCA; meanwhile, the changes of crystallographic preferred orientation of FLiNaK salt domains in SCA imply that the external load force makes better the ordered stacking of the larger crystal grains of the FLiNaK salt impregnated into graphite. Most importantly, we have found for the first time that the fracture position of graphite impregnated with FLiNaK salt always occurs near the SCA rather than at a fixed region under the external stress load. Thus, the present study not only helps to reveal the interaction mechanism between graphite and FLiNaK salt under the external stress load but also contributes to accurately predict and analyze the stress state of components, which would have an effective impact on the design of a molten salt reactor and the reliability of the component safety assessment.

Prediction of Carbon Partitioning and Austenite Stability via Non-equilibrium Thermodynamics in Quench and Partition (Q&P) Steel

Thermodynamics-based predictive modeling for phase characteristics after the quench and partition (Q&P) process is key to the design of new alloys and processing cycles with the best combination of mechanical properties. The austenite carbon content influences its phase stability during mechanical deformation and thus determines the improvement to total elongation from transformation-induced plasticity. The current article describes a carbon partition model based on para-equilibrium simulations with the addition of a temperature-dependent effective stored energy model that predicts carbon enrichment in austenite after Q&P processing. A retained austenite stability model is also proposed that uses the predicted carbon in austenite to quantify the austenite stability in terms of the Msσ temperature. The developed models were calibrated and subsequently validated using measurements from advanced characterization techniques such as local electrode atom probe tomography, synchrotron-based x-ray diffraction and uniaxial tensile tests at varying test temperatures.

X-ray nanotomography of coccolithophores reveals that coccolith mass and segment number correlate with grid size

Coccolithophores of the Noëlaerhabdaceae family are covered by imbricated coccoliths, each composed of multiple calcite crystals radially distributed around the periphery of a grid. The factors that determine coccolith size remain obscure. Here, we used synchrotron-based three-dimensional Coherent X-ray Diffraction Imaging to study coccoliths of 7 species of Gephyrocapsa, Emiliania and Reticulofenestra with a resolution close to 30 nm. Segmentation of 45 coccoliths revealed remarkable size, mass and segment number variations, even within single coccospheres. In particular, we observed that coccolith mass correlates with grid perimeter which scales linearly with crystal number. Our results indirectly support the idea that coccolith mass is determined in the coccolith vesicle by the size of the organic base plate scale (OBPS) around which R-unit nucleation occurs every 110–120 nm. The curvation of coccoliths allows inference of a positive correlation between cell nucleus, OBPS and coccolith sizes.

Phase transition and thermoelastic behavior of barite-group minerals at high-pressure and high-temperature conditions

Experimental studies on the phase transition and thermoelastic behavior of barite-group minerals are crucial to understand the recycle of sulfur in Earth’s interior. Here, we present a high-pressure and high-temperature (high P–T) study on two barite-group minerals—barite (BaSO4) and celestite (SrSO4) up to ~ 59.5 GPa 700 K and ~ 22.2 GPa, 700 K, respectively, using in situ synchrotron-based X-ray diffraction (XRD) combined with diamond anvil cells (DACs). Our results show that BaSO4 undergoes a pressure-induced phase transition from Pbnm to P212121 at ~ 20.3 GPa, which is different from the previous results. Upon decompression, the high-pressure phase of BaSO4 transforms back into its initial structure, which indicates a reversible phase transition. However, no phase transitions have been detected in SrSO4 over the experimental P–T range. In addition, fitting a third-order Birch–Murnaghan equation of state to the pressure–volume data yields the bulk moduli and their pressure derivatives of BaSO4 and SrSO4. Simultaneously, the thermal expansion coefficients of BaSO4 and SrSO4 are also obtained, by fitting the temperature-volume data to the Fei-type thermal equation of state. Furthermore, the compositional effects on the phase transformation and thermoelastic behavior of barite-group minerals are also discussed, and the results suggest that the bond length of (M=Ba, Sr, Pb) is an important factor that causes the phase transition pressure of SrSO4 to be the largest, PbSO4 is the second, and BaSO4 is the lowest.

Structural Correlation of Ferroelectric Behavior in Mixed Hafnia-Zirconia High-k Dielectrics for FeRAM and NCFET Applications

ABSTRACTThe recent discovery of ferroelectric behavior in doped hafnia-based dielectrics, attributed to a non-centrosymmetric orthorhombic phase, has potential for use in attractive applications such as negative differential capacitance field-effect-transistors (NCFET) and ferroelectric random access memory devices (FeRAM). Alloying with similar oxides like ZrO2, doping with specific elements such as Si, novel processing methods, encapsulation and annealing schemes are also some of the techniques that are being explored to target structural modifications and stabilization of the non-centrosymmetric phase. In this study, we utilized synchrotron-based x-ray diffraction in the grazing incidence in plane geometry (GIIXRD) to determine the crystalline phases in hafnia-zirconia (HZO) compositional alloys deposited by atomic layer deposition (ALD). Here we compare and contrast the structural phases and ferroelectric properties of mechanically confined HZO films in metal-insulator-metal (MIM) and metal-insulator-semiconductor (MIS) structures. Both MIM and MIS structures reveals a host of reflections due to non-monoclinic phases in the d-spacing region between 1.75Å to 4Å. The non-monoclinic phases are believed to consist of tetragonal and orthorhombic phases. Compared to the MIS structures a suppression of the monoclinic phase in MIM structures with 50% zirconia or less was observed. The correlation of the electrical properties with the structural analysis obtained by GIIXRD highlights the importance of understanding the effects of the underlying substrate (metal vs. Si) for different target applications.