Pair Distribution Function Analysis Research Articles

Pair distribution function analysis on nanocrystalline semiconductors ZnS and CdS

Nanosized Zinc sulfide (ZnS) and Cadmium sulfide (CdS) are essential materials for various applications, and understanding their atomic arrangement is critical for enhancing their performance. ZnS and CdS nanoparticles were synthesized via the chemical co-precipitation method using methacrylic acid as a surfactant. Angle dispersive x-ray diffraction (ADXRD), and pair distribution function (PDF) were utilized to evaluate structural parameters and atomic structures, respectively. It was confirmed that both samples have a Zink Blend structure. Optical properties and band gaps were estimated using UV–vis spectra. The PDF analysis provided detailed information on the Bravais lattices, lattice parameters, cation-cation, and cation–anion distances in ZnS and CdS. Our results show that methacrylic acid is an effective surfactant for synthesizing high-quality ZnS and CdS nanoparticles with well-defined atomic structures. Specifically, the cation–anion distance for Zn-S was found to be 0.2326 nm, and the cation-cation distance for Zn-Zn was 0.3798 nm, while the cation–anion distances for Cd-S and Cd-Cd were found to be 0.251 nm and 0.41 nm, respectively. Overall, our study demonstrates the effectiveness of PDF analysis in investigating the atomic structure of nanomaterials, and these findings could have important implications for the development of advanced nanomaterials for various applications.[copyright information to be updated in production process]

Detailed insights into the formation pathway of CdS and ZnS in solution: a multi-modal in situ characterisation approach.

The high stability, high availability, and wide size-dependent bandgap energy of sulphidic semiconductor nanoparticles (NPs) render them promising for applications in optoelectronic devices and solar cells. However, the tunability of their optical properties depends on the strict control of their crystal structure and crystallisation process. Herein, we studied the structural evolution during the formation of CdS and ZnS in solution by combining in situ luminescence spectroscopy, synchrotron-based X-ray diffraction (XRD) and pair distribution function (PDF) analyses for the first time. The influence of precursor type, concentration, temperature and heating program on the product formation and on the bandgap or trap emission were investigated in detail. In summary, for CdS, single-source precursor (SSP) polyol strategies using the dichlorobis(thiourea)cadmium(II) complex and double-source precursor approaches combining Cd(CH3COO)2·2H2O and thiourea led to the straightforward product at 100 °C, while the catena((m2-acetato-O,O')-(acetate-O,O')-(m2-thiourea)-cadmium) complex was formed at 25 and 80 °C. For ZnS, the reaction between Zn(CH3COO)2·2H2O and thiourea at 100 °C led to the product formation after the crystallisation and dissolution of an unknown intermediate. At 180 °C, besides an unknown phase, the acetato-bis(thiourea)-zinc(II) complex was also detected as a reaction intermediate. The formation of such reaction intermediates, which generally remain undetected applying only ex situ characterisation approaches, reinforce the importance of in situ analysis for promoting the advance on the production of tailored semiconductor materials.

Molecular dynamics simulations of GaAs crystal growth under different strains

The high-quality growth of GaAs crystals is extremely essential for the fabrication of high-performance high-frequency microwave electronic devices and light-emitting devices. In this work, the molecular dynamics (MD) simulation is used to simulate the induced crystallization of GaAs crystal along the [110] orientation. The effects of strain on the growth process and defect formation are analyzed by the largest standard cluster analysis, the pair distribution function, and visualization analysis. The results indicate that the crystallization process of GaAs crystal changes significantly under different strain conditions. At the initial stage, the crystal growth rate of the system decreases after a certain tensile strain and a large compressive strain have been applied, and the greater the strain, the lower the crystallization rate is. In addition, as the crystal grows, the system forms a zigzag interface bounded by the {111} facet, and the angle between the growth plane and the {111} facet affects the morphology of the solid-liquid interface and further affects the formation of twins. The larger the applied tensile strain and the smaller the angle, the more twin defects will form and the more irregular they will be. At the same time, a large proportion of the dislocations in the system is associated with twins. The application of strain can either inhibit or promote the nucleation of dislocations, and under an appropriate amount of strain size, crystals without dislocations can even grow. The study of the microstructural evolution of GaAs on an atomic scale provides a reference for crystal growth theory.

Atomic structural changes in the formation of transition metal tungstates: the role of polyoxometalate structures in material crystallization.

Material nucleation processes are poorly understood; nevertheless, an atomistic understanding of material formation would aid in the design of material synthesis methods. Here, we apply in situ X-ray total scattering experiments with pair distribution function (PDF) analysis to study the hydrothermal synthesis of wolframite-type MWO4 (M : Mn, Fe, Co, Ni). The data obtained allow the mapping of the material formation pathway in detail. We first show that upon mixing of the aqueous precursors, a crystalline precursor containing [W8O27]6- clusters forms for the MnWO4 synthesis, while amorphous pastes form for the FeWO4, CoWO4 and NiWO4 syntheses. The structure of the amorphous precursors was studied in detail with PDF analysis. Using database structure mining and an automated modelling strategy by applying machine learning, we show that the amorphous precursor structure can be described through polyoxometalate chemistry. A skewed sandwich cluster containing Keggin fragments describes the PDF of the precursor structure well, and the analysis shows that the precursor for FeWO4 is more ordered than that of CoWO4 and NiWO4. Upon heating, the crystalline MnWO4 precursor quickly converts directly to crystalline MnWO4, while the amorphous precursors transform into a disordered intermediate phase before the crystalline tungstates appear. Our data show that the more disordered the precursor is, the longer the reaction time required to form crystalline products, and disorder in the precursor phase appears to be a barrier for crystallization. More generally, we see that polyoxometalate chemistry is useful when describing the initial wet-chemical formation of mixed metal oxides.

Emerging disorder in Gd2(Ti1−xZrx)2O7 pyrochlores matrices for radioactive waste disposal: symmetry lowering versus defect clustering

The structure of Gd2(Ti1−xZrx)2O7 pyrochlores was investigated by means of synchrotron radiation powder diffraction, including pair distribution function analysis, Raman spectroscopy and DFT calculations to shed light on their rich defect chemistry.

Magnetic short-range order in polycrystalline SrGd2O4 and SrNd2O4 studied by reverse Monte Carlo simulations and magnetic pair-distribution function analysis

We present a study combining total-scattering powder neutron diffraction, reverse Monte Carlo simulations, and magnetic pair-distribution function analysis to deduce both the static and dynamic short-range magnetic spin correlations in two compounds of the rare-earth strontium oxides: ${\mathrm{SrGd}}_{2}{\mathrm{O}}_{4}$ and ${\mathrm{SrNd}}_{2}{\mathrm{O}}_{4}$. Both compounds exhibit a distorted honeycomb lattice which forms a set of zigzag ladders along the crystallographic $c$ axis of space group $Pnam$. Each set consists of two one-dimensional chains separated by diagonal rungs forming triangles, thus inducing a large degree of geometrical frustration due to the antiferromagnetic exchange between the magnetic ions. Significant magnetic diffuse scattering was observed well above the respective N\'eel temperatures and analyzed with reverse Monte Carlo techniques in reciprocal space. As a complementary analysis in real space we have derived the magnetic pair-distribution function for both compounds as a function of temperature. Our results clearly indicate that the individual zigzag ladders begin ordering well above ${T}_{\mathrm{N}}$ due to the dominating nearest and next-nearest interactions, long before interladder spin correlations become significant only slightly above ${T}_{\mathrm{N}}$. Additionally, for ${\mathrm{SrNd}}_{2}{\mathrm{O}}_{4}$ we find some qualitative differences between the short-range spin correlations above ${T}_{\mathrm{N}}$ and those observed in the ordered state.

Pair distribution function analysis driven by atomistic simulations: Application to microwave radiation synthesized TiO[formula omitted] and ZrO[formula omitted

A workflow is presented for performing pair distribution function (PDF) analysis of defected materials using structures generated from atomistic simulations. A large collection of structures, which differ in the types and concentrations of defects present, are obtained through energy minimization with an empirical interatomic potential. Each of the structures is refined against an experimental PDF. The structures with the lowest goodness of fit Rw values are taken as being representative of the experimental structure. The workflow is applied to anatase titanium dioxide (a-TiO2) and tetragonal zirconium dioxide (t-ZrO2) synthesized in the presence of microwave radiation, a low temperature process that generates disorder. The results suggest that titanium vacancies and interstitials are the dominant defects in a-TiO2, while oxygen vacancies dominate in t-ZrO2. Analysis of the atomic displacement parameters extracted from the PDF refinement and mean squared displacements calculated from molecular dynamics simulations indicate that while these two quantities are closely related, it is challenging to make quantitative comparisons between them. The workflow can be applied to other materials systems, including nanoparticles.

Node Distortion as a Tunable Mechanism for Negative Thermal Expansion in Metal–Organic Frameworks

Chemically functionalized series of metal-organic frameworks (MOFs), with subtle differences in local structure but divergent properties, provide a valuable opportunity to explore how local chemistry can be coupled to long-range structure and functionality. Using in situ synchrotron X-ray total scattering, with powder diffraction and pair distribution function (PDF) analysis, we investigate the temperature dependence of the local- and long-range structure of MOFs based on NU-1000, in which Zr6O8 nodes are coordinated by different capping ligands (H2O/OH, Cl- ions, formate, acetylacetonate, and hexafluoroacetylacetonate). We show that the local distortion of the Zr6 nodes depends on the lability of the ligand and contributes to a negative thermal expansion (NTE) of the extended framework. Using multivariate data analyses, involving non-negative matrix factorization (NMF), we demonstrate a new mechanism for NTE: progressive increase in the population of a smaller, distorted node state with increasing temperature leads to global contraction of the framework. The transformation between discrete node states is noncooperative and not ordered within the lattice, i.e., a solid solution of regular and distorted nodes. Density functional theory calculations show that removal of ligands from the node can lead to distortions consistent with the Zr···Zr distances observed in the experiment PDF data. Control of the node distortion imparted by the nonlinker ligand in turn controls the NTE behavior. These results reveal a mechanism to control the dynamic structure of MOFs based on local chemistry.

Tracking Sub-Nano-Scale Structural Evolution in Zeolite Synthesis by In Situ High-Energy X-ray Total Scattering Measurement with Pair Distribution Function Analysis.

The crystallization mechanism of zeolites remains unclarified to date because of lack of effective techniques in characterizing the local structures of amorphous precursors under synthetic conditions. Herein, in situ high-energy X-ray total scattering measurement with pair distribution function analysis is performed throughout the hydrothermal synthesis of SSZ-13 zeolite to investigate the amorphous-to-crystalline transformation at the sub-nano level in real time. Ordered four-membered rings (4Rs) are dominantly formed during the induction period, prior to the significant increase in the number of symmetric six- and eight-membered rings (6Rs and 8Rs) in the crystal growth stage. These preformed ordered 4Rs contribute to the formation of d6r and cha composite building units containing 6Rs and 8Rs with the assistance of the organic structure-directing agent, leading to the construction of embryonic zeolite crystallites, which facilitate the crystal growth through a particle attachment pathway. This work enriches the toolbox for better understanding the crystallization pathway of zeolites.

Alternate Synthesis Method for High‐Performance Manganese Rich Cation Disordered Rocksalt Cathodes

AbstractCation‐disordered rocksalt (DRX) cathodes have recently emerged as a promising class of cobalt‐free, high‐capacity cathodes for lithium‐ion batteries. To facilitate their commercialization, the development of scalable synthesis techniques providing control over composition and morphology is critical. To this end, a sol‐gel synthesis route to prepare Mn‐rich DRX cathodes with high capacities is presented here. Several compositions with varied Mn content and nominal F doping are successfully prepared using this technique. In‐situ X‐ray diffraction measurements demonstrate that DRX formation proceeds at moderate temperature (800 °C) through the sol‐gel route, which enables intimate mixing among reactive intermediate phases that form at lower temperatures. All synthesized compositions possess cation short‐range order, as evidenced by neutron pair distribution function and electron diffraction analysis. These DRX materials demonstrate promising electrochemical performance with reversible capacities up to 275 mAh g. Compared to the baseline oxide (Li1.2Mn0.4Ti0.4O2), the Mn‐rich compositions exhibit improved cycling stability, with some showing an increase in capacity upon cycling. Overall, this study demonstrates the feasibility of preparing high‐capacity DRX cathodes through a sol‐gel based synthesis route, which may be further optimized to provide better control over the product morphology compared to traditional synthesis methods.

Bibliometric review and recent advances in total scattering pair distribution function analysis: 21 years in retrospect

Bibliometric review and recent advances in total scattering pair distribution function analysis: 21 years in retrospect

Special quasirandom structures description of the local structure of disordered Bi0.5K0.5TiO3

Polar nanoregions (PNRs) are believed to play a decisive role in the local and macroscopic polarization in relaxor ferroelectrics. The limited microscopic understanding of the structure and dynamics of PNRs hampers the rational design of new lead-free materials. Here, the local structure of A-site disordered Bi0.5K0.5TiO3 (BKT) is investigated using synchrotron x-ray and neutron pair distribution function (PDF) analysis and density functional theory (DFT) optimized special quasirandom structures (SQSs). DFT-relaxed SQS with a 4 × 4 × 4 supercell size can reproduce the experimental PDFs of disordered BKT, as well as the partial PDFs and total polarization, with comparable results to those reported from a combined analysis of x-ray and neutron PDF data with large-box reverse Monte Carlo methods. We find that small Bi3+-rich polar clusters are likely to be the microscopic origin of relaxor behavior in disordered BKT, and that the existence of large polar nanoregions (PNRs) is not necessary to explain the relaxor properties. Our results also highlight the great potential of the SQS approach to gain a nanoscale-to-microscopic understanding of other relaxor solid solutions.

Synthesis of Catalytic Precursors Based on Mixed Ni-Al Oxides by Supercritical Antisolvent Co-Precipitation

Mixed Ni-Al oxide catalytic precursors with different elemental ratios (20, 50, and 80 wt.% Ni0) were synthesized using green supercritical antisolvent co-precipitation (SAS). The obtained oxide precursors and metal catalysts were characterized in detail by X-ray diffraction (XRD) analysis, atomic pair distribution function (PDF) analysis, CO adsorption, and high-resolution transmission electron microscopy (HRTEM). It was found that the composition and structure of the Ni-Al precursors are related to the Ni content. The mixed Ni1−xAlxO oxide with NiO-based crystal structure was formed in the Ni-enriched sample, whereas the highly dispersed NiAl2O4 spinel was observed in the Al-enriched sample. The obtained metal catalysts were tested in the process of anisole H2-free hydrogenation. 2-PrOH was used as a hydrogen donor. The catalyst with 50 wt.% Ni0 demonstrated the highest activity in the hydrogenation process.

Unravelling the convoluted and dynamic interphasial mechanisms on Li metal anodes.

Accurate understanding of the chemistry of solid-electrolyte interphase (SEI) is key to developing new electrolytes for high-energy batteries using lithium metal (Li0) anodes1. SEI is generally believed to be formed by the reactions between Li0 and electrolyte2,3. However, our new study shows this is not the whole story. Through synchrotron-based X-ray diffraction and pair distribution function analysis, we reveal a much more convoluted formation mechanism of SEI, which receives considerable contributions from electrolyte, cathode, moisture and native surface species on Li0, with highly dynamic nature during cycling. Using isotope labelling, we traced the origin of LiH to electrolyte solvent, moisture and a new source: the native surface species (LiOH) on pristine Li0. When lithium accessibility is very limited as in the case of anode-free cells, LiOH develops into plate-shaped large crystals during cycling. Alternatively, when the lithium source is abundant, as in the case of Li||NMC811 cells, LiOH reacts with Li0 to form LiH and Li2O. While the desired anion-derived LiF-rich SEI is typically found in the concentrated electrolytes or their derivatives, we found it can also be formed in low-concentration electrolyte via the crosstalk effect, emphasizing the importance of formation cycle protocol and opening up opportunities for low-cost electrolyte development.

Etched Silicon Planar CRL Optics for the High-Energy X-ray Diffraction Beamlines 11-ID-B and 11-ID-C at the APS

The focusing of high-energy X-rays is most commonly achieved by commercially available compound refractive lenses (CRL), which are added together in larger structures. There is a need for high-energy X-ray beamlines to enable focusing in only one dimension down to a few micrometers to study layered materials and thin films. High-energy X-rays above 50 keV require often 100 lenses or more, therefore it is more efficient to etch the complete arrays of lenses into a monolithic substrate like a silicon wafer. Custom lens arrays were fabricated for the high-energy x-ray beamlines 11-ID-B, and 11-ID-C at the Argonne National Laboratory. The fabrication required tuning parameters of the Bosch process to optimize the etching of deep vertical sidewalls at a reasonable speed without overheating. The beamline 11-ID-B is equipped with lens arrays of 85-110 lenses for 59 keV and 190-250 lenses for 87 keV photon energy, focusing the beam vertically below 5.0 µm at the sample positions between 1600 mm to 2100 mm. 11-ID-C has received arrays of 435 lenses that focus 106 keV X-rays to a vertical height of 2.0 µm at the sample position. In both cases, the flux density gain in the focal spot is larger than a factor of 20, relative to using slits to cut the beam size. The lens setup is permanently installed and can be moved in and out of the beam during the experiment without further alignment. The lenses have enabled operando diffraction studies on interfaces in batteries and the development of pair distribution function (PDF) analysis using grazing incidence geometry.

Designing Glass and Crystalline Phases of Metal-Bis(acetamide) Networks to Promote High Optical Contrast.

Owing to their high tunability and predictable structures, metal-organic materials offer a powerful platform to study glass formation and crystallization processes and to design glasses with unique properties. Here, we report a novel series of glass-forming metal-ethylenebis(acetamide) networks that undergo reversible glass and crystallization transitions below 200 °C. The glass-transition temperatures, crystallization kinetics, and glass stability of these materials are readily tunable, either by synthetic modification or by liquid-phase blending, to form binary glasses. Pair distribution function (PDF) analysis reveals extended structural correlations in both single and binary metal-bis(acetamide) glasses and highlights the important role of metal-metal correlations during structural evolution across glass-crystal transitions. Notably, the glass and crystalline phases of a Co-ethylenebis(acetamide) binary network feature a large reflectivity contrast ratio of 4.8 that results from changes in the local coordination environment around Co centers. These results provide new insights into glass-crystal transitions in metal-organic materials and have exciting implications for optical switching, rewritable data storage, and functional glass ceramics.

Enhanced Catalytic Performance of a Ce/V Oxo Cluster through Confinement in Mesoporous SBA-15.

To increase catalytic efficiency, mesoporous supports have been widely applied to immobilize well-defined metal oxide clusters due to their ability to stabilize highly dispersed clusters. Herein, a redox-active heterometallic Ce12V6-oxo cluster (CeV) was first presynthesized and then incorporated into mesoporous silica, SBA-15, via a straightforward impregnation method. Scanning transmission electron microscopy (STEM) and Fourier transform infrared spectroscopy (FTIR), in concert with scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS), verified the successful introduction of the CeV cluster inside the pore of SBA-15. The 51V magic angle spinning solid-state nuclear magnetic resonance (51V MAS NMR) spectroscopy and differential pair distribution function (dPDF) analysis confirmed the structural integrity of the CeV cluster inside the SBA-15. The composite was then benchmarked for liquid-phase oxidation of 2-chloroethyl ethyl sulfide (CEES) under mild conditions and gas-phase oxidative dehydrogenation (ODH) of propane under high temperatures (up to 550 °C). The catalytic reactivity results demonstrated 8- and 14-fold increase in turnover frequency (TOF) values of the composite (CeV@10SBA-2) than the bulk CeV cluster under the same conditions for CEES oxidation and ODH, respectively. These results highlight the improved reactivity of the catalytically active CeV cluster as attributed to the higher dispersion of the discrete cluster upon immobilization within the SBA-15 support.

Size and Strain of Zinc Sulfide Nanoparticles Altered by Interaction with Organic Molecules.

Nanosized zinc sulfides (nano-ZnS) have size-dependent and tunable physical and chemical properties that make them useful for a variety of technological applications. For example, structural changes, especially caused by strain, are pronounced in nano-ZnS < 5 nm in size, the size range typical of incidental nano-ZnS that form in the environment. Previous research has shown how natural organic matter impacts the physical properties of nano-ZnS but was mostly focused on their aggregation state. However, the specific organic molecules and the type of functional groups that are most important for controlling the nano-ZnS size and strain remain unclear. This study examined the size-dependent strain of nano-ZnS synthesized in the presence of serine, cysteine, glutathione, histidine, and acetate. Synchrotron total scattering pair distribution function analysis was used to determine the average crystallite size and strain. Among the different organic molecules tested, those containing a thiol group were shown to affect the particle size and size-induced strain most strongly when added during synthesis but significantly reduced the particle strain when added to as-formed nano-ZnS. The same effects are useful to understand the properties and behavior of natural nano-ZnS formed as products of microbial activity, for example, in reducing environments, or of incidental nano-ZnS formed in organic wastes.

Mechanochemical Synthesis and Study of the Local Structure of NaGaS2 Glass and Glass-Ceramics.

NaGaS2 is a newly discovered compound that has already shown great promise for a variety of applications because of its layered structure and ion exchange properties. In this work, crystalline NaGaS2 has been synthesized by an alternative method to what has been previously published, namely, by mechanochemistry, either by a direct one-step process or by a two-step process. In the one-step process, crystalline NaGaS2 is directly formed by milling sodium sulfide Na2S and gallium(III) sulfide Ga2S3. However, an amorphous material is present in majority together with the crystalline phase. In the two-step process, amorphous NaGaS2 is first obtained by mechanical milling and then heated above its glass transition temperature to obtain a glass-ceramic mainly composed of crystalline NaGaS2. For the two-step process, changes of the local atomic-level structure in amorphous NaGaS2 and after crystallization were analyzed by high-field solid-state nuclear magnetic resonance (NMR) spectroscopy as well as by X-ray total scattering and pair distribution function (PDF) analysis. Based on quantitative analysis on the 23Na NMR spectra, modifying the annealing treatment can promote the formation of the crystalline phase up to a molar fraction of 83.8%.

Partial breakdown of translation symmetry at a structural quantum critical point associated with a ferroelectric soft mode

We report that complete suppression of a phonon-driven structural phase transition causes partial breakdown of a three-dimensional translation symmetry in a well-defined sublattice. This state is revealed for a dielectric compound, ${\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{Al}}_{2}{\mathrm{O}}_{4}$, that comprises an ${\mathrm{AlO}}_{4}$ network incorporated into a hexagonal Ba(Sr) sublattice. Pair distribution function analyses and inelastic neutron scattering experiments provide clear-cut evidence of the ${\mathrm{AlO}}_{4}$ network forming a continuum of Al-O short-range correlations similar to glasses, whereas the Ba(Sr) sublattice preserves the original translational symmetry. This glassy network significantly dampens the phonon spectrum and transforms it into the broad one resembling those typically observed in glass materials.