High-energy Synchrotron X-ray Diffraction Research Articles

Systematic Operando Diffraction Study of Nickel-Rich LiNi1-x-YMnxCoyO2 Cathodes in Full Cells: Nickel-Content, Aging, Loading, Charge Rate, and Voltage Limit

High performance, single layer full pouch cells were constructed using LiNi1-x-yMnxCoyO2 (NCM) cathodes and graphite anodes and were measured in operando using high energy synchrotron X-ray diffraction. A variety of cell build parameters were constructed using nickel-rich NCM cathodes: LiNi0.5Co0.2Mn0.3O2 (NCM523), LiNi0.6Co0.2Mn0.2O2 (NCM622), LiNi0.8Co0.1Mn0.1O2 (NCM811). Two cathode loadings were used for analysis: low loading (round 1) cells (1.2-1.3 mAh/cm2) and high loading (round 2) cells (2.2-2.3 mAh/cm2). The experiments were divided into two parts: a study of nickel content and a study of aging. The first study analyzed the effect of nickel content (NCM523/NCM622/NCM811) with varying cell loadings (round 1 and round 2), charge rates (6C and C/2), and voltage limits (4.1V and 4.4V). The most stable configuration (NCM523) was used for an aging analysis with both round 1 and round 2 loadings analyzed at the freshly formatted state and the highly aged state (>1000 cycles). Operando data were collected in sequence with C/2, 2C, 4C, and 6C charge rates and C/2 discharge rate in all cases, with a 3-4.1 V window.

Visualizing Heterogeneous Lithium Plating and Stripping during Fast Charging

Lithium plating is an obstacle for the development of fast-charge batteries and enabling of widescale electric vehicle adoption. Synchrotron high-energy X-ray diffraction was used to directly identify and track lithium plating in a full LiNi0.5Mn0.3Co0.2O2 / graphite pouch cell operated with a 6C charge rate for greater than 1200 cycles. The magnitude and spatial distribution of lithium plating, lithium stripping, and the effect of plating on lithium intercalation into graphite were quantified. For discharged cell maps, irreversible and fully lithiated graphite (LiC6) was closely correlated with lithium plating and can be considered a highly reliable indicator of lithium plating in cases where plated lithium is below the detection sensitivity. Isolated regions of slight plating initially stripped to below the detection limit, but over time the coverage and amount of plated lithium increased while the stripping efficiency decreased. Long term monitoring of lithium formation in a fast-charge battery provides important information for a better understanding of lithium plating and stripping mechanisms in practical cells.

Interface-Mediated Twinning-Induced Plasticity in a Fine Hexagonal Microstructure Generated by Additive Manufacturing.

The grain size is a determinant microstructural feature to enable the activation of deformation twinning in hexagonal close-packed (hcp) metals. Although deformation twinning is one of the most effective mechanisms for improving the strength-ductility trade-off of structural alloys, its activation is reduced with decreasing grain size. This work reports the discovery of the activation of deformation twinning in a fine-grained hcp microstructure by introducing ductile body-centered cubic (bcc) nano-layer interfaces. The fast solidification and cooling conditions of laser-based additive manufacturing are exploited to obtain a fine microstructure that, coupled with an intensified intrinsic heat treatment, permits to generate the bcc nano-layers. In situ high-energy synchrotron X-ray diffraction allows tracking the activation and evolution of mechanical twinning in real-time. The findings obtained show the potential of ductile nano-layering for the novel design of hcp damage tolerant materials with improved life spans.

Deformation kinetics of a TRIP steel determined by in situ high-energy synchrotron X-ray diffraction

The microstructure design and the development of predictive approaches exploiting the transformation-induced plasticity (TRIP) effect require a keen understanding of the kinetics governing the strain-induced martensitic transformation. In this work, in situ high-energy synchrotron X-ray diffraction is applied to track the deformation kinetics of a commercial AISI 301LN metastable austenitic stainless steel in real-time. The kinetics obtained, providing the behaviour of the bulk material during room temperature tension up to a true strain of 0.3, unambiguously reveals the transformation sequence of ε and α′ martensite which is discussed with respect to the evolution of texture and slip. These results are enhanced with microstructure analysis including electron backscattered diffraction and transmission Kikuchi diffraction. The insights provided shed light on the role of ε during α′ transformation in metastable austenitic stainless steels and show that the latter is triggered by the general activation of slip.

Quantifying a partial polyamorphic transition in a cerium-based metallic glass during cooling

Cerium-based metallic glasses are prototype polyamorphous systems with pressure-induced polyamorphic transitions extensively reported. Cooling typically has a similar effect on materials as compression with regard to reducing volume. However, previous studies show dramatically different behavior of Ce-based metallic glasses between cooling and compression, whose origin remains unclear. Here, using in situ low-temperature synchrotron high-energy x-ray diffraction, the structural evolution of a Ce68Al10Cu20Co2 metallic glass is accurately determined and analyzed by a structure factor and a reduced pair distribution function (PDF) during cooling from 298 to 83 K. An unusually large linear thermal expansion coefficient is revealed, which is associated with both continuous but inconsistent structural changes between the two subpeaks of the first atomic shell in terms of average bond lengths and coordination numbers. These phenomena are suggested to be attributed to a gradual 4f electron delocalization of only a minimal amount (∼2.6% at 83 K) of Ce atoms by quantitative analysis of the PDF data. However, a previously expected global polymorphic transition from a low-density amorphous state to a high-density amorphous state with an abrupt volume collapse is not observed. Moreover, electrical resistivity also shows a continuous increase during cooling without any sharp change. It is clarified that cryogenic temperatures could facilitate but are not powerful enough alone to trigger a global polymorphic transition in the Ce68Al10Cu20Co2 metallic glass, suggesting a wide distribution of its local atomic environment.

In-situ quantification and density functional theory elucidation of phase transformation in carbon steel during quenching and partitioning

Phase transformation in low alloyed Fe-C steels during quenching and partitioning (Q&P), though authentically attributed to carbon diffusion, is scarcely quantified experimentally in terms of microstructural evolution and lack of fundamental backing at a quantum mechanics level. Herein, we report on a combined in-situ high energy synchrotron X-ray diffraction and density functional theory (DFT) study to unveil the physical mechanism of phase transformation in a Q&P processed advanced Fe-C steel. Beside a small fraction of bainite, a low air-quenching rate of ∼6 °C/s in the Ms to quenching temperature range leads to carbon enrichment into the untransformed austenite, which simultaneously turns up with the later stage of martensitic transformation at the existing austenite/martensite interfaces. The resulting transformations are ascertained by DFT results and attributed to a second energy barrier in ferrite/martensite facilitation to carbon diffusion to austenite at elevated temperatures, along with the well-known carbon solubility difference/equilibrium in austenite and martensite. The development of cubic martensite in the carbon steel is theoretically elucidated and attributed to more probable hopping sites and diffusion paths of carbon in the ferrite/martensite than in the austenite.

In situ high-energy X-ray diffraction of precipitation and dissolution reactions during heating of Al alloys

During heating of Al alloys, typically a sequence of precipitation and dissolution reactions occurs and the single (partly opposing) reactions superimpose. Differential scanning calorimetry (DSC) is one common technique to analyse the kinetic development of precipitation and dissolution in Al alloys, but the superposition of the exothermic precipitation and endothermic dissolution reactions complicates the DSC signal interpretation, as DSC measures the sum of any heat effect. Synchrotron high-energy X-ray diffraction (HEXRD) allows the kinetic development of phase transformations to be obtained and can support the separation of superimposed DSC signals. HEXRD results from this work offer a new approach to separate part of the superimposed reactions and their kinetic development for the equilibrium phases β-Mg2Si in EN AW-6082 and η-Mg(Zn,Cu,Al)2 in EN AW-7150. Comparing DSC and HEXRD results confirms serious overlap issues. Common DSC evaluation methods alone, using zero crossing between endothermic and exothermic heat flow or peak positions can be misleading regarding individual reaction start and finish temperatures as well as regarding reaction intensities, which can be unambiguously determined by in situ HEXRD.

Solidification texture, variant selection, and phase fraction in a spot-melt electron-beam powder bed fusion processed Ti-6Al-4V

The effect of a spot melt strategy on the solidification texture, variant selection, phase fraction, and their variations along the build height was investigated in comparison to a conventional linear melt strategy. Ti-6Al-4V alloy samples were manufactured by an electron-beam powder bed fusion process using two different melt strategies and characterized using high-energy synchrotron x-ray diffraction. The linear and spot melt cases resulted in β<100> cube and fiber textures, respectively, with the cube/fiber axis nearly parallel to the build direction. The α phase exhibited Burgers orientation relationship (BOR) with the parent β phase for both melt strategies. Although all of the key texture components and the BOR between the α and β phases were consistently observed in both cases along the build height, there were several measurable differences between the two. At the top of the build height, the β<100> build texture intensity was stronger in the linear case. However, the texture intensity in the linear case decreased gradually from the top to near the substrate, whereas the spot melt case did not show this trend. Moreover, the BOR was examined along the build height and the results showed that there is a distinct variant selection in the spot melt case, unlike the linear case. Specifically, the planar variants sharing ( 1 ̅ 01 ) β || ( 0002 ) α with [ 2 ̅ 2 ̅ 2 ̅ ] β and [ 2 2 ̅ 2 ] β were the most prominent in the spot melt, but no preference was identified in the directional variants. The β phase fraction was slightly lower in the spot melt case compared to the linear case. In both the cases, the β phase fraction decreased moving towards the substrate but remained significantly higher than that of the powder feedstock. Overall, the novel spot melt strategy produced a more homogeneous microstructure in terms of both the phase fraction and texture across the build height.

Refinements in phase fraction determination of textured alloys from transmission diffraction data

The use of high-energy synchrotron X-ray diffraction sources has become increasingly common for high-quality phase fraction measurements and microstructural evolution experiments. While the high flux, large volume illuminated and large number of diffraction vectors should reduce common sources of uncertainty and bias, the distribution of the diffraction vectors may still cause bias in the phase fraction measurement. This hypothesis of bias was investigated with example experimental data and synthetic data. The authors found that there may be bias depending on the sample texture, the distribution of diffraction vectors and the hkl planes used in the phase fraction measurement, even for nearly complete coverage of a pole figure. The authors developed a series of geometry-based correction values that reduced the measurement bias due to sampling scheme and texture in the phase fraction measurement by an order of magnitude. The efficacy of these corrections was demonstrated with application to both experimental and synthetic data.

On the thermodynamics and its connection to structure in the Pt-Pd-Cu-Ni-P bulk metallic glass forming system

Contrary to basic hard sphere structure models, recent studies revealed, significant structural differences between Pt-Cu-Ni-P and Pd-Cu-Ni-P metallic glass-forming liquids with the same stoichiometry. To cover the compositional space between both systems, platinum is subsequently replaced by palladium in the composition (Pt/Pd)42.5Cu27Ni9.5P21. For this systematic set of alloys, the thermodynamic properties, such as isobaric heat capacity, enthalpy and Gibbs free energy are assessed. A systematic drop of the Gibbs free energy difference between crystal and liquid, providing a lower estimate of the driving force for crystallization was observed, underlining the high glass-forming ability of the Pd-rich systems. Contrary to kinetic fragility data, a change of the thermodynamic fragility can be observed, drawing the picture of an increasing thermodynamically strong behavior with rising Pd-content. Further, the temperature induced changes of the total structure factors S(Q) were monitored using high-energy synchrotron X-ray diffraction. Focus was laid on the changes on the medium-range length scale, by analyzing changes of the first sharp diffraction peak. Here a good correlation of the changes in peak-width and the thermodynamic fragility was found. From the determination of the excess enthalpy, large amounts of residual enthalpy in the glassy state were observed for the Pt-rich alloys, supporting the increased ductility of these alloys. The current findings further carve out the different roles of the topologically similar Pt and Pd in the Pt/Pd-Cu-Ni-P alloy system and how the change of the structural motifs on the medium range order is influencing thermal properties such as enthalpy and heat capacity.

Dissimilar laser welding of a CoCrFeMnNi high entropy alloy to 316 stainless steel

In this work, laser welding of a rolled CoCrFeMnNi high entropy alloy to 316 stainless steel was performed. Defect-free joints were obtained. The microstructure evolution across the welded joints was assessed and rationalized by coupling electron microscopy, high energy synchrotron X-ray diffraction, mechanical property evaluation, and thermodynamic calculations. The fusion zone microstructure was composed of a single FCC phase, and a hardness increase at this location was observed. Such results can be attributed to the formation of a new solid solution (arising from the mixing of the two base materials). Moreover, the incorporation of carbon in the fusion zone upon melting of the stainless steel also aids in the strengthening effect observed. The welded joints presented good mechanical properties, with fracture occurring at the fusion zone. This can be ascribed to the non-favourable, i.e., large grain size, microstructure that developed at this location.

Revealing causes of macroscale heterogeneity in lithium ion pouch cells via synchrotron X-ray diffraction

Heterogeneous battery performance is a critical issue for maximization of cell lifetime capacity and safety. Using high energy synchrotron X-ray diffraction, the influence of charge rate, voltage limit, uneven stack pressure, and gas generation on the lithium transport properties was quantified in single-layer graphite/LiNi 0.5 Mn 0.3 Co 0.2 O 2 pouch cells. A freshly formatted cell tracked in operando during initial fast charge cycles indicated variable position-dependent performances, while lateral mapping showed a significant fast charge (6C) heterogeneity compared to slow charge (C/2). Pressure effects were non-dominant compared to charge rate. Maps of previously aged and rested cells indicate that lateral heterogeneity slowly equilibrates at rest, but regenerates upon further cycling at fast charge rate. Furthermore, an unformatted cell was mapped at charge and discharge during its first formation cycle to analyze the effect of byproduct gases on the heterogeneous lithium transport. Gas was observed as randomly interspersed “bubbles” which locally hindered lithium intercalation and caused significant heterogeneity. Electrode architectures and charging protocols that promote homogeneous intercalation are critical for predictable high-performance and long-life batteries. • In situ diffraction mapping elucidates lateral lithium heterogeneity in batteries. • Fast charging causes substantial heterogeneity in both anode and cathode. • Anode and cathode heterogeneity are inversely correlated in the early cycles. • Lithium heterogeneity is metastable and will equilibrate over time at rest. • Trapped gas during formation cycling creates electrochemically inert regions.

The boson peak and the first sharp diffraction peak in (As2S3)x(GeS2)1–x glasses

The parameters of the boson peak (BP) and the first sharp diffraction peak (FSDP) in (As2S3)x(GeS2)1x glasses measured using high-resolution Raman spectroscopy and high-energy synchrotron X-ray diffraction measurements are examined as a function of x. It has been found that there is no correlation between the positions of BP and FSDP. The BP position shows a nonlinear composition behavior with a maximum at about x = 0.4, whereas the FSDP position changes virtually linearly with x. The intensities of both BP and FSDP show nonlinear composition dependences with the slope changes at x = 0.4, although there is no direct proportionality. Analysis of the partial structure factors for the glasses with x = 0.2, 0.4 and 0.6 obtained in another study has shown that the cation-cation atomic pairs of Ge–Ge, Ge–As and As–As make the largest contribution to FSDP, where the Ge–Ge and Ge–As pairs are dominant.

In Situ Scattering Studies of Crystallization Kinetics in a Phase-Separated Zr–Cu–Fe–Al Bulk Metallic Glass

Thermal stability and the crystallization kinetics of a phase-separated Zr–Cu–Fe–Al bulk metallic glass were investigated using in situ high-energy synchrotron X-ray and neutron diffraction, as well as small-angle synchrotron X-ray scattering. It was revealed that this glass with excellent glass-forming ability possesses a two-step crystallization behavior. The crystalline products and their evolution sequence are more complicated than a homogeneous Zr–Cu–Al glass with average glass-forming ability. The experimental results indicate that a finely distributed nanometer-sized cubic Zr2Cu phase forms first and then transforms to a tetragonal Zr2Cu phase, while the matrix transforms to an orthorhombic Zr3Fe phase. The strength of the Zr–Cu–Fe–Al composite containing cubic Zr2Cu phase and glass matrix increases, and the plasticity also improves compared to the as-cast Zr–Cu–Fe–Al bulk metallic glass. Our results suggest that the formation of multiple and complex crystalline products would be the characteristics of the Zr–Cu–Fe–Al glass with better glass-forming ability. Our study may shed light on the synthesis of bulk-sized glass–nanocrystals composites of high strength and good plasticity.

Nanoscale structural analysis of Bi0.5Na0.5TiO3 in high-temperature phases

We performed a local structure analysis of the ferroelectric perovskite Bi0.5Na0.5TiO3 (BNT) in high-temperature tetragonal and cubic phases by combining high-energy synchrotron X-ray diffraction and atomic pair-distribution function. BNT is a promising lead-free piezoelectric material, although it has the problem of narrow working temperature range due to its low depolarization temperature. Since the depolarization temperature of BNT is caused by a diffuse order-disorder phase transition similar to a relaxer ferroelectrics, local structural analysis over a wide temperature range is required to elucidate the depolarization phenomenon. Using this approach, we found that the local structure is largely contributed by the diffuse component, and the deviation from the average structure is caused by the shift of Bi atoms. The amount of shift increased with increasing temperature. Changes in nanoscale structure with distance are closely related to BNT depolarization phenomena. The results show the model needed to develop highly functional piezoelectric materials.

Revealing intrinsic and extrinsic piezoelectric contributions in phase coexistence system of PbTiO3-BiScO3

PbTiO3-BiScO3 ceramics possess high piezoelectricity and high Curie temperature simultaneously, presenting a very promising candidate for high-temperature actuators and transducers. Figuring out the underlying piezoelectric mechanisms is of great importance for its application. Herein, we reveal the quantified intrinsic and extrinsic contributions to the high electrostrain of the morphotropic composition with phase coexistence by employing the advanced in situ electrical biasing high-energy synchrotron X-ray diffraction combined with the STRAP (strain, texture, and Rietveld analysis for piezoceramics from diffraction) methodology. An electric field-induced phase transformation is observed between the coexisting tetragonal and rhombohedral phases. It is found that the tetragonal phase contributes most of the domain switching strain, while the predominant lattice strain is from the rhombohedral phase. With phase fraction changes, the quantitative results demonstrate that the field-induced electrostrain is mainly contributed by the intrinsic lattice strain. In contrast, the high irreversible domain switching strain dominates the large remanent strain. It implies that transforming the large remanent strain into reversible strain would be a strategic direction to improve the piezoelectric response. The present results provide a further understanding of the high piezoelectricity and could help to advance the application of PbTiO3-BiScO3.

Step-wise R phase transformation rendering high-stability two-way shape memory effect of a NiTiFe-Nb nanowire composite

In this work, we designed a NiTiFe-Nb nanowire composite to achieve a high-stability and small-hysteresis R phase two-way shape memory effect (TWSME). The R-phase TWSME was achieved in the composite in an annealed state without thermomechanical training due to the inherent internal stresses associated with the Nb nanowires, as demonstrated by in situ synchrotron high-energy X-ray diffraction. Transmission electron microscopic analysis also revealed some details of the R-phase transformation process, which render an explanation of the high cyclic stability of the R-phase TWSME. The R-phase transformation in this NiTiFe-Nb nanowire composite was found to proceed over several stages, including the formation of precursor nanodomains of partial lattice distortion for the R phase, the formation of R phase particles of coordinated orientations, the coalescence of the R phase particles into selected plate variants of preferential orientations for TWSME, and the continued evolution of the R phase crystallographic structure for further TWSME with zero hysteresis. Such step-wise process of the R-phase transformation divides the total TWSME strain into segments of smaller magnitudes in the macroscopic behavior, and more importantly reduces the discrete lattice distortion mismatch at the transformation interface on the microscopic scale. This drastically reduces the chances of generating dislocations during the transformation process, thus rendering the high cyclic stability of the R-phase TWSME. Such intricate behavior may be closely related to the unique NiTiFe matrix – Nb nanowire microstructure and its unique inherent internal stress condition.

Cycling Rate-Induced Spatially-Resolved Heterogeneities in Commercial Cylindrical Li-Ion Batteries.

Synchrotron high-energy X-ray diffraction computed tomography has been employed to investigate, for the first time, commercial cylindrical Li-ion batteries electrochemically cycled over the two cycling rates of C/2and C/20. This technique yields maps of the crystalline components and chemical species as a cross-section of the cell with high spatiotemporal resolution (550 × 550 images with 20 × 20 × 3 µm3 voxel size in ca. 1 h). The recently developed Direct Least-Squares Reconstruction algorithm is used to overcome the well-known parallax problem and led to accurate lattice parameter maps for the device cathode. Chemical heterogeneities are revealed at both electrodes and are attributed to uneven Li and current distributions in the cells. It is shown that this technique has the potential to become an invaluable diagnostic tool for real-world commercial batteries and for their characterization under operating conditions, leading to unique insights into "real" battery degradation mechanisms as they occur.

Microscopic Structural Evolution during Ultrastable Metallic Glass Formation.

By decreasing the rate of physical vapor deposition, ZrCuAl metallic glasses with improved stability and mechanical performances can be formed, while the microscopic structural mechanisms remain unclear. Here, with scanning transmission electron microscopy and high-energy synchrotron X-ray diffraction, we found that the metallic glass deposited at a higher rate exhibits a heterogeneous structure with compositional fluctuations at a distance of a few nanometers, which gradually disappear on decreasing the deposition rate; eventually, a homogeneous structure is developed approaching ultrastability. This microscopic structural evolution suggests the existence of the following two dynamical processes during ultrastable metallic glass formation: a faster diffusion process driven by the kinetic energy of the depositing atoms, which results in nanoscale compositional fluctuations, and a slower collective relaxation process that eliminates the compositional and structural heterogeneity, equilibrates the deposited atoms, and strengthens the local atomic connectivity.

Temperature-dependent structure of 1-propanol/water mixtures: X-ray diffraction experiments and computer simulations at low and high alcohol contents

Aqueous mixtures of 1-propanol have been investigated by high-energy synchrotron X-ray diffraction upon cooling. X-ray weighted total scattering structure factors of 6 mixtures, from 8 mol% to 89 mol% alcohol content, as well as that of pure 1-propanol are reported from room temperature down to the freezing points of the liquids. Molecular dynamics simulations have been performed, in order to interpret measured data. The all atom OPLS-AA potential model was used for 1-propanol, combined with both the SPC/E and the TIP4P/2005 water models: both combinations provide a semi-quantitative description of the measured total structure factors at low and high alcohol contents, while the agreement is qualitative for the mixture with 71 mol% of 1-propanol. From the simulated particle configurations, partial radial distribution functions were calculated. Furthermore, detailed description of the hydrogen bonded network is provided, in terms of hydrogen bond numbers, analysis of proton donor–acceptor ratios, size distributions of hydrogen bonded clusters and ring size statistics. Strong temperature dependence of the percolation threshold, as well as of the participation of the number of doubly hydrogen bonded molecules in cyclic entities, has been found for the mixture with 89 mol% of 1-propanol. Above an alcohol content of 20 mol%, 5-fold rings are the most frequent cyclic entities, with a strong temperature dependence in terms of the number of rings.