Situ Synchrotron X-ray Powder Diffraction Research Articles

Control of the pore chemistry in metal-organic frameworks for efficient adsorption of benzene and separation of benzene/cyclohexane

Control of the pore chemistry in metal-organic frameworks for efficient adsorption of benzene and separation of benzene/cyclohexane

Highly Efficient Proton Conduction in the Metal-Organic Framework Material MFM-300(Cr)·SO4(H3O)2.

The development of materials showing rapid proton conduction with a low activation energy and stable performance over a wide temperature range is an important and challenging line of research. Here, we report confinement of sulfuric acid within porous MFM-300(Cr) to give MFM-300(Cr)·SO4(H3O)2, which exhibits a record-low activation energy of 0.04 eV, resulting in stable proton conductivity between 25 and 80 °C of >10–2 S cm–1. In situ synchrotron X-ray powder diffraction (SXPD), neutron powder diffraction (NPD), quasielastic neutron scattering (QENS), and molecular dynamics (MD) simulation reveal the pathways of proton transport and the molecular mechanism of proton diffusion within the pores. Confined sulfuric acid species together with adsorbed water molecules play a critical role in promoting the proton transfer through this robust network to afford a material in which proton conductivity is almost temperature-independent.

Fischer–Tropsch Synthesis: Effect of the Promoter’s Ionic Charge and Valence Level Energy on Activity

In this contribution, we examine the effect of the promoter´s ionic charge and valence orbital energy on the catalytic activity of Fe-based catalysts, based on in situ synchrotron X-ray powder diffraction (SXRPD), temperature-programmed-based techniques (TPR, TPD, CO-TP carburization), and Fischer–Tropsch synthesis catalytic testing studies. We compared the promoting effects of K (a known promoter for longer-chained products) with Ba, which has a similar ionic radius but has double the ionic charge. Despite being partially “buried” in a crystalline BaCO3 phase, the carburization of the Ba-promoted catalyst was more effective than that of K; this was primarily due to its higher (2+) ionic charge. With Ba2+, higher selectivity to methane and lighter products were obtained compared to the K-promoted catalysts; this is likely due to Ba´s lesser capability of suppressing H adsorption on the catalyst surface. An explanation is provided in terms of a more limited mixing between electron-filled Ba2+ 5p and partially filled Fe 3d orbitals, which are expected to be important for the chemical promotion, as they are further apart in energy compared to the K+ 3p and Fe 3d orbitals.

Multiple Anionic Transition-Metal Oxycarbide for Better Lithium Storage and Facilitated Multielectron Reactions.

As an important class of multielectron reaction materials, the applications of transition-metal oxides (TMOs) are impeded by volume expansion and poor electrochemical activity. To address these intrinsic limitations, the renewal of TMOs inspires research on incorporating an advanced interface layer with multiple anionic characteristics, which may add functionality to support properties inaccessible to a single-anion TMO electrode. Herein, a transition-metal oxycarbide (TMOC, M = Mo) with more than one anionic species was prepared as an interface layer on a corresponding oxide. A multiple anionic TMOC possesses advantages of structural stability, abundant active sites, and elevated metal cation valence states. Such merits mitigate volume changes and enhance multielectron reactions significantly. The TMOC nanocomposite has a well-maintained capacity after 1000 cycles at 2 A·g-1 and fully resumed rate performance. In situ synchrotron X-ray powder diffraction (SXRPD) analysis unveils negligible volume expansions occurring upon oxycarbide layer coupling, with lattice spacing variation less than 1% during cycling. The lithium storage mechanism is further inspected by combined analysis of kinetics, SXRPD, and first-principles calculations. Superior to TMO, multielectron reactions of the TMOC electrode have been boosted due to easier rupture of the metal-oxygen bond. Such improvements underscore the importance of incorporating an oxycarbide configuration as a strategy to expand applications of TMOs.

Time-Resolved Synchrotron Powder X-ray Diffraction Studies on the Synthesis of Li8SiO6 and Its Reaction with CO2.

Lithium oxosilicate was synthesized via the solid-state method using Li2O and SiO2 as starting reactants. In situ synchrotron powder X-ray diffraction (SPRXD) coupled with Rietveld refinement allowed describing the synthesis as a two-step process where Li2O and SiO2 react to form Li4SiO4 and, at higher temperatures, lithium orthosilicate reacts with the remaining Li2O to form Li8SiO6. Time-resolved measurements allowed determining the temperatures at which each phase transformation occurs as well as the time required to complete the synthesis. The CO2 capture properties of Li8SiO6 in the temperature range from room temperature to 770 °C were studied in detail by time-resolved in situ SPXRD. The crystallographic phases present during Li8SiO6 carbonation were identified and quantified via Rietveld analysis. Results showed that, within the temperature range from 200 to 690 °C, Li8SiO6 carbonation produces Li4SiO4 and Li2CO3, while, at temperatures from 690 to 750 °C, a secondary reaction occurs, where previously formed Li4SiO4 reacts with CO2, producing Li2SiO3 and Li2CO3. These findings allowed proposing a mechanism of reaction for Li8SiO6 carbonation in the temperature range that is of interest for high temperature solid-state sorbents.

Design and Synthesis of Layered Na2Ti3O7 and Tunnel Na2Ti6O13 Hybrid Structures with Enhanced Electrochemical Behavior for Sodium-Ion Batteries.

A novel complementary approach for promising anode materials is proposed. Sodium titanates with layered Na2Ti3O7 and tunnel Na2Ti6O13 hybrid structure are presented, fabricated, and characterized. The hybrid sample exhibits excellent cycling stability and superior rate performance by the inhibition of layered phase transformation and synergetic effect. The structural evolution, reaction mechanism, and reaction dynamics of hybrid electrodes during the sodium insertion/desertion process are carefully investigated. In situ synchrotron X‐ray powder diffraction (SXRD) characterization is performed and the result indicates that Na+ inserts into tunnel structure with occurring solid solution reaction and intercalates into Na2Ti3O7 structure with appearing a phase transition in a low voltage. The reaction dynamics reveals that sodium ion diffusion of tunnel Na2Ti6O13 is faster than that of layered Na2Ti3O7. The synergetic complementary properties are significantly conductive to enhance electrochemical behavior of hybrid structure. This study provides a promising candidate anode for advanced sodium ion batteries (SIBs).

In Situ Synchrotron X-ray Diffraction Analysis of the Setting Process of Brushite Cement: Reaction and Crystal Growth.

Brushite cements are fast self-setting materials that can be used as bone substitute materials. Although tracing their fast setting process is a challenge, it is important for the understanding of the same, which in turn is important for the material's further development and use in the clinics. In this study, the setting rate, phase formation, and crystal growth of brushite cements were quantitatively studied by in situ synchrotron powder X-ray diffraction (SXRD) on a time scale of seconds. The influence of reactant ratios and a retardant (citric acid) on the setting reaction were analyzed. To complement the in situ investigations, scanning electron microscopy was carried out for ex situ morphological evolution of crystals. The initial reaction followed a four-step process, including a fast nucleation induction period, nucleation, crystal growth, and completion of the setting. The brushite crystal size grew up to the micro scale within 1 min, and the brushite content increased linearly after the nucleation until all monocalcium phosphate monohydrate (MCPM; Ca(H2PO4)2·H2O) had dissolved within minutes, followed by a slow increase until the end of the monitoring. By adjusting the MCPM to the β-tricalcium phosphate (β-TCP, β-Ca3(PO4)2) ratio in the starting powders, the brushite/monetite ratio in the cements could be modified. In the presence of citric acid, the formation of brushite nuclei was not significantly retarded, whereas the increase in brushite content and the growth of crystal size were effectively hindered. The amount of monetite also increased by adding citric acid. This is the first time that the brushite setting process has been characterized in the first seconds and minutes of the reaction by SXRD.

Separating plasticity-induced closure and residual stress contributions to fatigue crack retardation following an overload

The introduction of an overload or underload within a constant amplitude loading fatigue test leads to a retardation or acceleration of the Fatigue Crack Growth Rate (FCGR). The understanding of the causes of these effects is essential in the context of variable amplitude fatigue loading, since in principle any loading history can be represented as a sequence of overloads and underloads. In the case of overload, along with some other minor causes, the residual stress changes at the crack tip and crack closure behind the tip can be thought of as the main factors that affect the fatigue crack growth rate. Whilst this has been recognised and accepted for many decades, controversy persists regarding the relative significance and presence of these two effects, and consensus is yet to emerge. The effect of crack closure, when the baseline loading ratio is high enough, can be inhibited so that the main cause of retardation becomes doubtless the residual stress present ahead the crack tip.In the present paper we report our attempt to deconvolve the contributions of crack closure and residual stress on crack retardation following an overload. To accomplish this task we analyse the results of fatigue tests run at two baseline load ratios, namely R=0.1 and R=0.7. At the load ratio of R=0.7 the crack closure effect is not operative, as confirmed by Digital Image Correlation analysis of the crack flanks close to the tip, and post mortem fractographic analysis of crack surfaces. Therefore, for R=0.7 the compressive residual stress region created by the overload ahead of the crack tip is the sole mechanism causing crack retardation. Therefore, for R=0.7 the focus must be placed entirely on the strain field around the crack tip. To this end, line profiles along the crack bisector of elastic strain in the crack opening direction were collected at several stages of crack propagation past the overload using in situ Synchrotron X-ray Powder Diffraction (SXRPD) technique.By performing comparison between the two loading conditions (R=0.7 and R=0.1), information was extracted regarding the role of residual stress alone, and then, by subtracting this effect for the R=0.1 sample, for crack closure alone. To enable this analysis, we propose a introducing the concept of equivalent effective stress intensity factor range, ∆Keq,eff proposed by Walker. Afterwards, the SIF range reduction ratio, β, which represents the “knock down” factor with respect to the steady state growth was assessed. It is in terms of these newly introduced parameters that the magnitude and extent of the overload-induced crack growth rate retardation can be plotted, fitted and decomposed into closure and residual stress effects, respectively. It is concluded that although the residual stress effect is present at all values of the load ratio R, its effect is relatively short-lived, whilst the closure effect that is dominant at low values of R causes longer range retardation.

Insights into formation and stability of τ-MnAlZx (Z = C and B)

The τ-phase MnAl alloys are promising candidate for rare earth free permanent magnets. In this study, In order to better understand the MnAl ε→τ phase transition mechanism in a continuous cooling process and metastable MnAl τ-phase high temperature stability, Mn0.54Al0.46, Mn0.55Al0.45C0.02 and Mn0.55Al0.45B0.02 alloys were systematically studied by in situ synchrotron X-ray powder diffraction (SR-XRD). The relationship between τ-phase formation tendency and different cooling rates of Mn0.55Al0.45C0.02 was investigated. Besides, the high temperature stabilities of undoped τ-MnAl and carbon/boron doped τ-MnAl were studied. Differential thermal analysis (DTA) was also employed to study the phase transformation as well. The research results show that a high cooling rate of 600 °C/min leads to a 50/50 wt% mixture of ε- and τ-phase; almost pure τ-phase was obtained when cooled at a moderate cooling rate of 10 °C/min; while for a slow cooling rate of 2 °C/min, the τ-phase partially decomposed into β and γ2 phases. No intermediate ε’-phase was observed during the ε→τ phase transition during the experiments. For the boron and carbon doped τ-MnAl, the 800 °C high temperature stability experiments reveal that C stabilizes the τ-MnAl while doped B destabilises the tetragonal structure and it decomposes into β- and γ2-phases.

Long Duration Studies of Li-Ion Battery Materials Using Synchrotron X-Ray Powder Diffration

The Long Duration Experiment (LDE) Facility on Beamline I11 at Diamond Light Source is the first of its kind, allowing in situ synchrotron X-ray powder diffraction (SXPD) data to be collected on a weekly basis for extended periods of time (a few months up to a few years). The facility is capable of housing multiple experiments simultaneously, and even though data are only collected at weekly intervals the experiments remain in place and all sample environments (high/low temperature, humidity, electrochemical cycling) are maintained throughout the duration of the experiment. The increasing demand for large-scale energy storage (e.g. electric vehicles) means that new materials, with much higher Li+ storage capabilities and longer lifetimes than are currently available are required to meet this demand. Many promising candidates for such materials are known but before these can become commercially available their chemical/structural stability and electrochemical cycling performance need to be well understood. In-situ powder diffraction has proven to be an extremely useful technique for just this, providing an insight into the complex chemical process that take place during charge/discharge cycling. Standard in situ experiments using existing facilities are, however, often limited to short periods of time, from a few hours up to a few (2-3) days, and therefore, only allow the first few cycles (often at accelerated charging rates) of the material to be observed. The result is that the material characteristics may be well understood for the first cycle but little is known about the long term processes that ultimately lead to failure of the cell over longer timescales. With a specially designed coin cell holder (Figure 1 inset) and dedicated multi-channel Arbin battery cyclers it is an ideal facility for the long term study of both existing and novel battery materials. This setup allows data to be collected over many hundreds of cycles at slower, more realistic, rates without the need for accelerated cycling therefore better simulating battery use under real-life conditions. To achieve this, a new in situ cell was developed through the modification of a standard CR2032 coin cell which allows for the transmission of X-rays while retaining the integrity and impermeability of the stainless steel case and therefore allowing the cell to perform well for long periods of time. Details of the facility and the modified coin cells will be presented along with preliminary results of the first long term battery studies, of a selection of Li-based electrodes (commercial and novel materials), to demonstrate the capabilities of this facility and the quality of the data produced. Figure 1

Phase equilibria of Ce–Mg–Ni ternary system at 673 K and hydrogen storage properties of selected alloy

The isothermal section of Ce–Mg–Ni ternary system at 673 K was constructed through thermodynamic calculation coupled with experimental verification. Under guidance of the phase diagram in Mg-rich corner, Ce2.92Mg91.84Ni5.24 was designed to investigate its hydrogen storage properties. Moreover, the mechanism of α-to-β (α: diluted phase and β: hydride) phase transformation in the Ce2.92Mg91.84Ni5.24–H2 system was elucidated by in situ synchrotron powder X-ray diffraction (SR-PXRD). The alloy showed a good activated ability and displayed two plateaus in the pressure–composition–temperature curves. The kinetic mechanisms of hydriding and dehydriding reactions were analyzed by Chou model. The rate-controlling steps were the diffusion for the initial stage in hydriding reaction and the surface penetration for dehydriding reaction. SR-PXRD patterns indicated that the activated Ce2.92Mg91.84Ni5.24 gradually transformed into CeH2.51, (Mg) (with solid solution of H atoms) and Mg2NiH0.3, finally transformed into CeH2.51, MgH2 and Mg2NiH4 during the first hydriding process.

Dynamic strain propagation in nanoparticulate zirconia refractory

Residual and intrinsic strains in granular materials have been studied extensively. However, understanding the dynamic strains that cause these resultant residual strains is key to developing better strain-resistant materials. This investigation demonstrates a method for characterizing dynamic strain propagation in granular materials. The specimen is a zirconia-based refractory composed of sol–gel-derived zirconia nanoparticles in a potassium silicate glass binder.In situsynchrotron X-ray powder diffraction in flat-plate geometry is used to characterize the sample structure on timescales of the order of 1 ms. A 125 W CO2laser is used to strain the sample with a 25 ms pulse length. To compensate for the poor flux on this timescale, a pump–probe method is repeated 1000 times and the resulting data are subsequently re-binned to improve statistics. A Gaussian weighting function is also used to introduce better contrast between strained and unstrained frames.TOPAS Academicis used for fitting with a Le Bail model in `batch mode'. Lattice parameters and sample height are refined during fitting, along with a Lorentzian line width for extracting microstrain broadening. Microstrains, ∊, in the range of 1.01 < ∊ < 1.46% are reported on a 1 ms timescale.

High-pressure structural properties of naphthalene up to 6 GPa

The elastic and structure behavior of solid naphthalene (C10H8) was studied byin situsynchrotron powder X-ray diffraction up to 5.6 GPa in a diamond anvil cell. Rietveld refinements were applied to obtain atomic coordinates and lattice parameters as a function of pressure. Within the studied pressure range, the intramolecular C—C and C—H distances decrease by 3.5%, whereas intermolecular distances within and between the herringbone layers decrease by 18 and 10%, respectively. Noindication of a symmetry change (space groupP21/a) was observed. A markedly anisotropic compression is preserved up to 5.6 GPa, with linear compressibilities βa:βb:βc:β[200]≃ 7:5:3:10. Fitting of theP–Vexperimental data to the Vinet equation of state yieldsK0= 7.9 (3) GPa andK′ = 7.5 (3) atV0= 361 Å3. At the highest pressure of 5.6 GPa, the unit-cell volume is decreased by 23%. The overall regularity of compression confirms the absence of major structural transformations in naphthalene up to 5.6 GPa. However, a distinct bend of the pressure dependence of the interlayer C...C distances observed at 2 GPa suggests a minor structural irregularity, which is apparently associated with spectroscopic anomalies observed previously.

Halide Substitution in Magnesium Borohydride

The synthesis of halide-substituted Mg(BH4)2 by ball-milling, and characterization with respect to thermodynamics and crystal structure, has been addressed. The ball-milled mixture of Mg(BH4)2 and MgX2 (X = Cl, Br) has been investigated by in situ/ex situ synchrotron powder X-ray diffraction (SR-PXD), differential scanning calorimetry (DSC), and infrared and Raman spectroscopy. High resolution SR-PXD patterns reveal that the unit cell volume of β-Mg(BH4)2 in milled and annealed mixtures of Mg(BH4)2 with MgCl2/MgBr2 is smaller than that of pure β-Mg(BH4)2. This is due to substitution of BH4– by Cl–/Br– ions which have ionic radii smaller than that of BH4–. For comparison, ab initio calculations were run to simulate Cl substitution in α-Mg(BH4)2. The α-polymorph was used rather than the β-polymorph because the size of the unit cell was more manageable. Electronic energy data and thermodynamic considerations confirm the miscibility of MgCl2 and Mg(BH4)2, both in α- and β-polymorphs.

Selective hydrogen absorption from gaseous mixtures by BCC Ti-V alloys

Hydrogen absorption behaviour of the BCC Ti-V alloys has been studied as related to their potential application for the selective hydrogen absorption from mixtures with active gases containing CO and steam at high temperatures. Alloys and their hydrides were characterised using Scanning Electron Microscopy (SEM), Thermal Desorption Spectroscopy (TDS), Temperature Programmed Reaction (TPR) and in situ synchrotron X-ray powder diffraction (SR-XRD). BCC Ti0.8V0.2 and Ti0.9V0.1 were able to absorb 3.95 wt.% H by forming a FCC type hydride γ−(Ti,V)H2. Nanoparticles of Pd and Pd/Pt were electroless deposited on the surface of the hydrides to catalyse hydrogen absorption. TPR tests showed that such alloys were capable of absorbing hydrogen even when substantial amounts of CO and H2O were present in the gas stream. Nanoparticles of Pd/Pt provide a better performance as compared to Pd alone. In situ SR-XRD has been used to probe the mechanisms of hydrogenation and dehydrogenation.

Anin situsynchrotron X-ray powder diffraction study of size dependent phase transitions in nanostructured ZrO2-Sc2O3solid solutions

An<i>in situ</i>synchrotron X-ray powder diffraction study of size dependent phase transitions in nanostructured ZrO₂-Sc₂O₃solid solutions

Real-time synchrotron powder X-ray diffraction study of the antisite defect formation during sub- and supercritical synthesis of LiFePO4and LiFe1−xMnxPO4nanoparticles

In situsynchrotron powder X-ray diffraction (PXRD) is used to study the formation of LiFePO4nanoparticles during hydrothermal synthesis from LiOH, H3PO4, and two different iron precursors, FeSO4and (NH4)2Fe(SO4)2. Furthermore, the synthesis of Li(Fe1−xMnx)PO4(x= 0.25, 0.50 and 0.75) from LiOH, H3PO4and FeSO4/MnSO4is studied. The reactions involve an unknown intermediate phase, which is not the previously observed intermediate NH4FePO4·H2O. The intermediate phase quickly transforms into LiFePO4and Li(Fe1−xMnx)PO4even at rather low temperatures. The presence of ammonium enhances the formation of LiFePO4, and it also leads to a significant reduction in the concentration of Li–Fe antisite defects. Thein situPXRD technique allows one to follow the influence of time, temperature and manganese doping on the antisite defect concentration, and it is shown that even under supercritical conditions a reaction time of several minutes is required to suppress the defects. This makes flow synthesis of defect-free LiFePO4and Li(Fe1−xMnx)PO4nanoparticles challenging.

Structural and microstructural changes during anion exchange of CoAl layered double hydroxides: anin situX-ray powder diffraction study

Anion-exchange processes in cobalt–aluminium layered double hydroxides (LDHs) were studied byin situsynchrotron X-ray powder diffraction (XRPD). The processes investigated were CoAl–CO3→ CoAl–Cl → CoAl–CO3, CoAl–Cl → CoAl–NO3and CoAl–CO3→ CoAl–SO4. The XRPD data show that the CoAl–CO3→ CoAl–Cl process is a two-phase transformation, where the amount of the CoAl–CO3phase decreases exponentially while that of the CoAl–Cl phase increases exponentially. Energy-dispersive X-ray spectroscopy (EDXS) studies of a partially chloride-exchanged CoAl–CO3LDH sample along within situXRPD data suggested that the individual particles in the CoAl–CO3sample are generally anion-exchanged with chloride one at a time. In contrast with the CoAl–CO3→ CoAl–Cl transformation, the XRPD data show that the reverse CoAl–Cl → CoAl–CO3process is a one-phase transformation. Rietveld refinements indicate that the occupancy factors of the carbon and oxygen sites of the carbonate group increase, while that of the chloride site decreases. In the CoAl–Cl → CoAl–NO3anion-exchange reaction, the XRPD patterns reveal the existence of two intermediate phases in addition to the initial CoAl–Cl and final CoAl–NO3phases. Thein situdata indicate that one of these intermediates is a mixed nitrate- and chloride-based LDH phase, where the disorder decreases as the nitrate content increases. The XRPD data of the partial CoAl–CO3→ CoAl–SO4anion-exchange reaction show that the process is a two-phase transformation involving a sulfate-containing LDH with a 1H polytype structure.

In situsynchrotron powder X-ray diffraction studies of catalytic materials

<i>In situ</i>synchrotron powder X-ray diffraction studies of catalytic materials

Experimental studies of α-AlD3 and α′-AlD3versus first-principles modelling of the alane isomorphs

The thermal phase behaviour of cryomilled α′-AlD3 and α-AlD3 was investigated by in situsynchrotron powder X-ray diffraction (SR-PXD), differential scanning calorimetry and first principles atomic modelling. In situ measurements showed that α′-AlD3 decomposes directly into Al and D2 at around 80 °C during heating at 1 °C min−1. At higher temperatures the transformation of α′-AlD3 to α-AlD3 was observed by DSC measurements at 5 °C min−1, and tentatively by in situSR-PXD at 1 °C min−1. Atomic modelling was carried out to investigate possible structural relationships and transformation pathways between the α- and α′-phase. Group–subgroup relation analyses and direct method lattice dynamics were used to rule out a possible displacive transformation pathway between the α′- and α-phases. The likelihood of a reconstructive transformation was demonstrated by partial transformation of an interface between α′ and α domains during elevated temperature molecular dynamics. Such an α′- to α-phase transformation may be possible when kinetic barriers can be overcome at elevated temperatures or during long time periods. These insights are also relevant to the transformation mechanisms of the β-AlD3 and γ-AlD3 isomorphs to the α-phase.