Time-resolved X-ray Powder Diffraction Research Articles

Deciphering the structural dynamics in molten salt-promoted MgO-based CO2 sorbents and their role in the CO2 uptake.

The development of effective CO2 sorbents is vital to achieving net-zero CO2 emission targets. MgO promoted with molten salts is an emerging class of CO2 sorbents. However, the structural features that govern their performance remain elusive. Using in situ time-resolved powder x-ray diffraction, we follow the structural dynamics of a model NaNO3-promoted, MgO-based CO2 sorbent. During the first few cycles of CO2 capture and release, the sorbent deactivates owing to an increase in the sizes of the MgO crystallites, reducing in turn the abundance of available nucleation points, i.e., MgO surface defects, for MgCO3 growth. After the third cycle, the sorbent shows a continuous reactivation, which is linked to the in situ formation of Na2Mg(CO3)2 crystallites that act effectively as seeds for MgCO3 nucleation and growth. Na2Mg(CO3)2 forms due to the partial decomposition of NaNO3 during regeneration at T ≥ 450°C followed by carbonation in CO2.

Monitoring polymorphic transition of a cocrystal to a salt using time-resolved X-ray powder diffraction and solid-state nuclear magnetic resonance spectroscopy

Monitoring polymorphic transition of a cocrystal to a salt using time-resolved X-ray powder diffraction and solid-state nuclear magnetic resonance spectroscopy

Kinetics in the gas adsorption process of porous coordination polymers by time-resolved X-ray powder diffraction measurement

Kinetics in the gas adsorption process of porous coordination polymers by time-resolved X-ray powder diffraction measurement

Strain wave pathway to semiconductor-to-metal transition revealed by time-resolved X-ray powder diffraction

One of the main challenges in ultrafast material science is to trigger phase transitions with short pulses of light. Here we show how strain waves, launched by electronic and structural precursor phenomena, determine a coherent macroscopic transformation pathway for the semiconducting-to-metal transition in bistable Ti3O5 nanocrystals. Employing femtosecond powder X-ray diffraction, we measure the lattice deformation in the phase transition as a function of time. We monitor the early intra-cell distortion around the light absorbing metal dimer and the long range deformations governed by acoustic waves propagating from the laser-exposed Ti3O5 surface. We developed a simplified elastic model demonstrating that picosecond switching in nanocrystals happens concomitantly with the propagating acoustic wavefront, several decades faster than thermal processes governed by heat diffusion.

Intercalates of Bi2Se3 studied in situ by time-resolved powder X-ray diffraction and neutron diffraction.

Intercalation of lithium and ammonia into the layered semiconductor Bi2Se3 proceeds via a hyperextended (by >60%) ammonia-rich intercalate, to eventually produce a layered compound with lithium amide intercalated between the bismuth selenide layers which offers scope for further chemical manipulation.

A Flow-Through Reaction Cell for Studying Minerals Leaching by In-Situ Synchrotron Powder X-ray Diffraction

A flow-through reaction cell has been developed for studying minerals leaching by in-situ time-resolved powder X-ray diffraction, allowing for a better understanding of the leaching mechanisms and kinetics. The cell has the capability of independent control of temperature (up to 95 °C) and flow rate (>0.5 mL min−1) for atmospheric pressure leaching. It was successfully tested at the powder diffraction beamline at the Australian Synchrotron. Galena powder was leached in a citrate solution under flow-through condition at a flow rate of 0.5 mL min−1, while diffraction patterns were collected during the entire leaching process, showing rapid galena dissolution without the formation of secondary mineral phases. The flow-through cell can be used to study leaching processes of other ore minerals.

In Situ Time-Resolved Decomposition of β-Hydride Phase in Palladium Nanoparticles Coated with Metal-Organic Framework

The formation of palladium hydrides is a well-known phenomenon, observed for both bulk and nanosized samples. The kinetics of hydrogen adsorption/desorption strongly depends on the particle size and shape, as well as the type of support and/or coating of the particles. In addition, the structural properties of hydride phases and their distribution also depend on the particle size. In this work, we report on the in situ characterization of palladium nanocubes coated with HKUST-1 metal-organic framework (Pd@HKUST-1) during desorption of hydrogen by means of synchrotron-based time-resolved X-ray powder diffraction. A slower hydrogen desorption, compared to smaller sized Pd nanoparticles was observed. Rietveld refinement of the time-resolved data revealed the remarkable stability of the lattice parameters of α- and β-hydride phases of palladium during the α- to β- phase transition, denoting the behavior more similar to the bulk materials than nanoparticles. The stability in the crystal sizes for both α- and β-hydride phases during the phase transition indicates that no sub-domains are formed within a single particle during the phase transition.

The unique interplay between copper and zinc during catalytic carbon dioxide hydrogenation to methanol

In spite of numerous works in the field of chemical valorization of carbon dioxide into methanol, the nature of high activity of Cu/ZnO catalysts, including the reaction mechanism and the structure of the catalyst active site, remains the subject of intensive debate. By using high-pressure operando techniques: steady-state isotope transient kinetic analysis coupled with infrared spectroscopy, together with time-resolved X-ray absorption spectroscopy and X-ray powder diffraction, and supported by electron microscopy and theoretical modeling, we present direct evidence that zinc formate is the principal observable reactive intermediate, which in the presence of hydrogen converts into methanol. Our results indicate that the copper–zinc alloy undergoes oxidation under reaction conditions into zinc formate, zinc oxide and metallic copper. The intimate contact between zinc and copper phases facilitates zinc formate formation and its hydrogenation by hydrogen to methanol.

Sintering kinetics of nanocrystalline Ce0.9Zr0.1O2 prepared by gel combustion method

The sintering process of nanometric Ce0.9Zr0.1O2 mixed oxides prepared by the amino acid–nitrate gel combustion method was analyzed by dilatometry using the constant heating rate (CHR) and stepwise isothermal dilatometry (SID) methods. The morphology of the mixed oxides was studied by scanning and transmission electron microscopies. The evolution of crystallite size with temperature was analyzed by time-resolved X-ray powder diffraction with synchrotron radiation. The sintering behavior resulted dependent on the morphology of the powders. Samples with nanometric crystallite size start to sinter even 500 K before than micrometric sample. We concluded that sintering process of nanometric Ce0.9Zr0.1O2 is controlled by grain-boundary diffusion for temperatures below 1373–1573 K, depending on the morphology of the sample. At high temperature, the grain-boundary and lattice diffusion become parallel controlling mechanism for sintering.

Sub-lattice polarization states in anti-ferroelectrics and their relaxation process

We report studies of quasi-remanent polarization states in Pb0.99Nb0.02[(Zr0.57Sn0.43)0.94Ti0.06]0.98O3 (PNZST) anti-ferroelectric ceramics and investigation of their relaxation effects using unique in-situ electrically activated time-resolved Synchrotron X-ray powder diffraction (SXPD) and 119Sn Mössbauer Spectroscopy (MS). The SXPD patterns are consistent with a phase transition from quasi-tetragonal perovskite in 0 V relaxed anti-ferroelectric state to rhombohedral distortion in ferroelectric state under saturating applied voltages of ±2 kV. The observed quasi-remanent polarization relaxation processes are due to the fact that tetragonal to rhombohedral distortion does not occur at the applied voltage required to access the quasi-remanent polarization states, and the tetragonal symmetry restored after the removal of the applied electric field is preserved. Since these quasi-remanent polarization states were seen as possibly suitable for memory applications, the implications of this study are that anti-ferroelectrics are more feasible for multi-state dynamic random access memories (DRAM), while their application to non-volatile memories requires development of more sophisticated “read-out” protocols, possibly involving dc electrical biasing.

Electrospray Mass Spectrometry Investigation into the Formation of CPO-27

Electrospray ionization mass spectrometry (ESI-MS) has been utilized to investigate the self-assembly processes occurring during the formation of the microporous metal–organic framework CPO-27-M (M = Co, Ni). The mono- and dinuclear building units {M(Hxdhtp)} and {M2(Hxdhtp)}, where Hxdhtp is the organic linker HxC8O6 and fragments thereof, were identified as key species present in the reaction mixture during the product formation. Time-resolved powder X-ray diffraction analysis was used to follow the synthesis and confirmed that no other crystalline products occur in the reaction mixture prior to the crystallization of CPO-27-Ni. When equimolar reactions were performed at room temperature, compounds [(M(H2dhtp)(H2O)4·2H2O] (M = Co, Ni) crystallized instead of CPO-27 obtained at the higher temperature of the solvothermal procedure. It was confirmed that mono- and dinuclear species are key building blocks not only in the formation of CPO-27-M but also in the formation of the 1D chain structure (M(H2dhtp)(H...

Thermal stability of the layered modification of Cu0.5ZrTe2 in the temperature range 25–900 °C

The thermal stability of the layered modification of the Cu0.5ZrTe2 polycrystalline intercalation compound, synthesized at room temperature, has been studied in the temperature range 25-900 °C. A change in the occupation of the octahedral and tetrahedral coordinated sites in the interlayer space of the zirconium ditelluride was observed using in-situ time-resolved synchrotron X-ray powder diffraction experiments. The formation of the rhombohedral CuZr2Te4 phase, which is stable in the temperature range 300-700 °C, has been observed. The copper intercalation at room temperature leads to the formation of a phase in which the Cu atoms occupy only octahedral sites in the interlayer space. At temperatures above the decay temperature of the rhombohedral CuZr2Te4, a layered phase with Cu atoms uniformly distributed between octahedral and tetrahedral sites in the interlayer space is stable. The changes in the crystal structure independent of temperature are in agreement with the previously proposed model, according to which the stability of the layered or the rhombohedral phase is determined by the entropy factor associated with the distribution of the intercalated atoms between the octahedral and tetrahedral sites in the interlayer space.

Time-Resolved Powder X-ray Diffraction of the Solvothermal Crystallization of Cobalt Gallate Spinel Photocatalyst Reveals Transient Layered Double Hydroxides

High energy X-ray diffraction is used to follow in situ the crystallization of a cobalt gallate from metallic gallium under solvothermal conditions in an aminoalcohol, revealing the formation and decay of transient metastable layered double hydroxides. Photocatalytic studies show the spinel product has activity as a water oxidation catalyst for oxygen evolution.

Time-Resolved X-Ray Powder Diffraction Study of Photoinduced Phase Transitions in Ti3 O5 Nanoparticles.

Nanoparticles of Ti3 O5 have been reported to show a permanent photoinduced phase transition at room temperature. This suggests that light-induced phase transformations of Ti3 O5 nanoparticles may be promising for technological applications. Here, we report a photoinduced semiconductor-to-metal phase transition from β-Ti3 O5 to λ-Ti3 O5 nanoparticles at room temperature observed directly by time-resolved X-ray powder diffraction in a pump-probe setup. The results show a partial structural change, limited by differences between pumped and probed volumes, which persists a few microseconds after excitation. The first step in the relaxation back to the ground state can be described by a single exponential decay with time constant within microsecond timescales. Analysis of the change in lattice constants enables us to estimate an average temperature increase across the phase transition, consistent with a thermally driven process.

Application of combined multivariate techniques for the description of time-resolved powder X-ray diffraction data

In this work, multivariate statistical techniques are employed to determine patterns and conversion curves from time-resolved X-ray powder diffraction data. For these purposes, time-window statistical total correlation spectroscopy is introduced for the pattern matching of the crystalline phase and is shown to be effective even in the case of overlapping peaks. When combined with evolving factor analysis and multivariate curve resolution–alternating least squares, this technique allows a definite estimation of patterns and conversion curves. The procedure is applied to in situ synchrotron powder diffraction patterns to monitor the setting reaction of magnesium potassium phosphate ceramic (MKP) from magnesia (MgO) and potassium dihydrogen phosphate. It is shown that the phases involved in the reaction are clearly distinguished and their evolution is correctly described. The conversion curves estimated with the proposed procedure are compared with the ones determined with the peak integration method, leading to an excellent agreement (Pearson's correlation coefficient equal to 0.9995 and 0.9998 for MgO and MKP, respectively). The approach also allows for the detection and description of the evolution of amorphous phases that cannot be described through conventional analysis of powder diffraction data.

In Situ Observation of Polymorphic Transition during Crystallization of Organic Compounds Showing Preferential Enrichment By Means Of Temperature-Controlled Video-Microscopy and Time-Resolved X-ray Powder Diffraction

A solvent-assisted solid-to-solid polymorphic transition, which was assumed to be one of the key processes for the occurrence of preferential enrichment (PE), has been proven to occur by means of temperature-controlled video-microscopy (TCVM) and time-resolved in situ X-ray powder diffraction (XRPD) measurement during crystallization of two typical first-generation chiral racemic compounds (1 and 2) showing an excellent PE phenomenon.

Mythen detector for X-ray diffraction at the Beijing synchrotron radiation facility

ABSTRACTTime-resolved X-ray powder diffraction may be used to elucidate the structure of polycrystalline matter, but a fast-response full-profile detector is often necessary. This article describes a Mythen detector incorporated in beamline 4B9A of the Beijing Synchrotron Radiation Facility. Basic parameters of this detector are reported, and flat-field correction, angular calibration, eccentric error, and other data treatment for this detector are discussed. X-ray diffraction measurement of lanthanum boride demonstrates that this detector provides high-quality, time-resolved X-ray powder diffraction measurements.

Combining high time and angular resolutions: time-resolved X-ray powder diffraction using a multi-channel analyser detector

The design and testing of the new MAD-STROBO data acquisition system are reported. The system realizes stroboscopic collection of high-resolution X-ray powder diffraction profiles under a dynamically applied electric field. It synchronizes an externally applied stimulus and detected X-ray photons. The feasibility of detecting sub-millidegree shifts of powder diffraction profiles with microsecond time resolution is demonstrated. MAD-STROBO may be applied for the investigation of various macroscopic and domain-related processes induced by an external perturbation, such as elasticity or piezoelectricity.

Phase transition of nanoparticulate LiFePO4during high rate cycling

A fundamental understanding of an electrode material requires the elucidation of its phase transformation mechanism during charge and discharge. Ex situ methods, which are carried out under equilibrium condition, have been widely used in charactering the thermodynamic phases at different states of charge, from which a thermodynamic phase transformation pathway can be constructed. However, ex situ measurements do not always reflect the process occurred in an operating battery as the non-equilibrium operating condition might result in deviations from the thermodynamic process, especially for high-rate materials, such as LiFePO4, which is predicted to exhibit a fundamentally different phase transformation process at high rates [1,2]. To probe the process at high rate, an in situ method with reasonable temporal resolution must be employed. In this work, the high rate galvanostatic cycling process of LiFePO4 nanoparticle electrode in a customised AMPIX cell [3] was investigated in situ by time-resolved synchrotron X-ray powder diffraction. Formation of continuous non-equilibrium solid solution phases between LiFePO4 and FePO4 was observed at 10 C rate. The in situ diffraction patterns were analysed by a refinement strategy that accounts for the asymmetrical diffraction peak profiles due to Li composition variations.

In situ synchrotron X-ray powder diffraction study of the early age hydration of cements blended with zeolitite and quartzite fines and water-reducing agent

A comparison was made between the early-age hydration of cements blended with micronized zeolitite and quartzite powders. The Portland cement replacement in the mixes was 30%, and the effect of introducing a superplasticiser to lower the required water to solid ratio was assessed. The cement pastes were hydrated at 40°C and monitored in situ by time-resolved synchrotron X-ray powder diffraction combined with Rietveld quantitative phase analysis.The quantitative evolution of phase weight fractions showed that the addition of the zeolite tuff accelerated the hydration rate of the main C3S cement component. Blending with the quartzite powder of similar fineness did not affect the C3S hydration rate. Reduction of the water to solid ratio by introduction of the superplasticiser had a retarding effect on the hydration of the zeolitite-blended cement over the early hydration period up to 3days.The AFt or ettringite reaction products, formed promptly after the addition of water to the mixtures, underwent a crystal structural modification over the induction period up to 4 to 6hours of reaction. The continuous contraction of the c-cell parameter and expansion of the a-cell parameter towards the ideal values for AFt or ettringite reflects the structural adaptation of the AFt to the changing availability of sulphate over the course of the first hours of hydration. The observed structural changes were less pronounced in the zeolitite blended cement. This is related to the dilution of the overall sulphate content in the blended cement and highlights the need to control and optimise sulphate additions in blended cements.