Atomic Pair Distribution Function Research Articles

Analyzing the atomic pair distribution function of BMT-based nanopowders via X-ray diffraction

In this study, we investigate the three-dimensional atomic structure of 0.65[Ba(Mg1/3, Ti2/3)]−0.35[BaTiO3] (BMT-BT) using x-ray diffraction (XRD) with molybdenum radiation (MoKα 1), Rietveld refinement, and the atomic pair distribution function (PDF) technique. We provide an analysis of the advantages of the PDF method for studying the unit cell of electroceramics. The XRD results show that BMT has a bulk crystal structure with a cubic perovskite structure. The new structural information enhances our understanding of the dielectric properties of BMT. The PDF analysis reveals that the average interatomic bond distance in the octahedral TiO6 atomic bond is around 2.8 Å, and the first peak at r = 1.39 Å corresponds to the nearest neighbor M-O distance (M = Ti, Mg, Nb). Additionally, the peak at r = 2.4 Å corresponds to the Ba-O and O-O distances in the MO6 octahedron. Peaks in the PDF data below 1 Å are ignored as they have no physical implications.

3D Covalent Polyoxovanadate‐Organic Framework as an Anode for High‐Performance Lithium‐Ion Batteries

AbstractPolyoxometalates (POMs), as a unique class well‐defined metal‐oxo clusters with excellent multielectron redox properties, have attracted extensive attention in the field of energy storage and conversion, but it is still challenging to achieve their highly uniform and stable monodispersed. In this study, for the first time, polyoxovanadate (POV) is used, (NH4)2[VIV3VV3O10{NH2C(CH2O)3}3] (tris‐V6O19), as nodes and successfully obtain a 3D covalent polyoxovanadate‐organic framework through a green hydrothermal synthesis method, termed POF‐1. Total scattering atomic pair distribution function analysis confirms that POF‐1 has a noninterpenetrated diamond‐like framework, fully exposing the monodispersed tris‐V6O19, effectively utilizing the active components of VIV/VV and enhancing surface mass transfer. Notably, POF‐1 demonstrates exceptional performance in lithium‐ion batteries, achieving a high reversible capacity of 887.4 mAh g−1 at 0.1 A g−1 and retaining over 92% capacity at 1 C during 1000 cycles. Electrochemistry mechanism and density functional theory calculations reveal that V centers in tris‐V6O19 and carbonyls (C═O) in BDOEB linkers are the main active sites, with each POF‐1 fragment capable of storing up to 14 Li+. This study opens a new pathway for the efficient and green synthesis of new 3D well‐defined POM‐organic frameworks, and shows great application prospect in the field of energy storage.

Origin of medium-range atomic correlation in simple liquids: Density wave theory

The atomic pair-distribution function of simple liquid and glass shows exponentially decaying oscillations beyond the first peak, representing the medium-range order (MRO). The structural coherence length that characterizes the exponential decay increases with decreasing temperature and freezes at the glass transition. Conventionally, the structure of liquid and glass is elucidated by focusing on a center atom and its neighboring atom shell characterized by the short-range order (SRO) and describing the global structure in terms of overlapping local clusters of atoms as building units. However, this local bottom-up approach fails to explain the strong drive to form the MRO, which is different in nature from the SRO. We propose to add an alternative top-down approach based upon the density wave theory. In this approach, one starts with a high-density gas state and seeks to minimize the global potential energy in reciprocal space through density waves using the pseudopotential. The local bottom-up and global top-down driving forces are not mutually compatible, and the competition and compromise between them result in a final structure with the MRO. This even-handed approach provides a more intuitive explanation of the structure of simple liquid and glass.

Towards scanning nanostructure X-ray microscopy.

This article demonstrates spatial mapping of the local and nanoscale structure of thin film objects using spatially resolved pair distribution function (PDF) analysis of synchrotron X-ray diffraction data. This is exemplified in a lab-on-chip combinatorial array of sample spots containing catalytically interesting nanoparticles deposited from liquid precursors using an ink-jet liquid-handling system. A software implementation is presented of the whole protocol, including an approach for automated data acquisition and analysis using the atomic PDF method. The protocol software can handle semi-automated data reduction, normalization and modeling, with user-defined recipes generating a comprehensive collection of metadata and analysis results. By slicing the collection using included functions, it is possible to build images of different contrast features chosen by the user, giving insights into different aspects of the local structure.

Combined atomic pair distribution function and EXAFS analysis of local structural study of MoTe2

Combined atomic pair distribution function and EXAFS analysis of local structural study of MoTe₂

Ceria–Zirconia Supported Platinum Catalysts for Water Gas Shift Reaction: Influence of Support Composition

The study is presented on the influence of the composition of a ceria-zirconia support on the structure and the activity in water gas shift reaction of platinum catalysts (Pt/Ce0.75Zr0.25O2 и Pt/Ce0.4Zr0.5Y0.05La0.05O2). The structure diagnostics of the samples were performed using high-resolution transmission electron microscopy, powder X-ray diffraction, CO chemisorption and X-ray atomic pair distribution function method. It was shown that the catalysts contain highly dispersed platinum particles not exceeding 2 nm in size. Platinum particles supported on Ce0.75Zr0.25O2 are smaller due to the higher specific surface area of the support. The catalysts Pt/Ce0.75Zr0.25O2 and Pt/Ce0.4Zr0.5Y0.05La0.05O2 proved to have similar efficiency while having the same platinum content. It was assumed that the catalysts supported on Ce0.4Zr0.5Y0.05La0.05O2 demonstrate a slightly higher turnover frequency per platinum surface atom, but it is likely compensated by the difference in the supported metal particle size.

Exploring the impact of incoherent Compton scattering on X-ray pair distribution function analysis of disordered materials

X-ray atomic pair distribution function (XPDF) measurements using a two-dimensional area detector have been of great value in studying atomic structures of materials with varying degrees of disorder. However, an area detector does not have energy resolution. Thus, incoherent inelastic Compton scattering and fluorescence are not discriminated, contaminating coherent elastic scattering. This paper investigates the effects of random noise from incoherent scattering on XPDF analysis. To conduct the study, the elastic scattering, Compton scattering and fluorescence of In0.33Ga0.67As alloy were separately measured using an intrinsic Ge solid-state detector with energy resolution. It is found that the addition of Compton scattering with a noise-to-signal ratio of about 0.8% results in the smearing of diffuse scattering in the high-Q region. Moreover, adding extra noise from fluorescence increases the smearing, overwhelming the diffuse scattering. Additionally, simulated data of elastic and Compton scattering on ferroelectric Ba(Ti0.8Zr0.2)O3 were used to investigate the evolution of noise fluctuation and its effects on the XPDF as a function of total intensity.

Ethanol-water motifs-A re-interpretation of the double-difference pair distribution functions of aqueous iron oxide nanoparticle dispersions.

In dispersion, nanoparticles can interact with the surrounding dispersion medium, such that an interfacial region with a structure differing from that of the bulk exists. Distinct nanoparticulate surfaces induce specific degrees of interfacial phenomena, and the availability of surface atoms is a crucial prerequisite for interfacial restructuring. Here, we investigate the nanoparticle-water interface of 0.5-10 wt. % aqueous iron oxide nanoparticle dispersions of 6nm diameter in the presence of 6 vol. % ethanol with x-ray absorption spectroscopy (XAS) and atomic pair distribution function (PDF) analysis. The absence of surface hydroxyl-groups in XAS spectra is in accordance with the double-difference PDF (dd-PDF) analysis, due to a fully covered surface from the capping agent. The previously observed dd-PDF signal is not stemming from a hydration shell, as postulated in Thomä et al. [Nat Commun. 10, 995 (2019)], but from the residual traces of ethanol from nanoparticle purification. With this article, we provide an insight into the arrangement of EtOH solutes in water at low concentration.

Crystal and local structures of La2Co7H obtained by synchrotron X-ray total scattering

We investigated the crystal and local structures of La2Co7Hx using synchrotron X-ray diffraction (SXRD) in the first absorption process. La2Co7 with a Ce2Ni7-type structure was transformed into La2Co7H7.4 with an orthorhombic structure (space group: Pbcn), determined by Rietveld refinement, through the formation of La2Co7H4.1. The expansions of the lattice parameters of La2Co7H7.4 from the original alloy were Δa = −3.2 %, Δb = −3.4 %, and Δc = 29.2 %. The unit cell expanded anisotropically. The local structure of La2Co7Hx (x = 0, 4.1, and 7.4) was determined by performing an atomic pair distribution function (PDF) analysis. The results showed no significant difference between the crystal and local structures of La2Co7 and La2Co7H4.1. The refined structural parameters of La2Co7H7.4 obtained by the PDF analysis were inconsistent with the Rietveld analysis results. The local distortion was not negligible, and the local atomic positions of the metal atoms deviated from the crystal structure. The local distortion of the CaCu5-type cell of La2Co7H7.4 was greater than that of the MgZn2-type cell.

Three-dimensional charge density wave in the dual heavy fermion system UPt2Si2

Heavy fermion liquids offer via their Kondo lattice diverse possibilities for exotic ground states. Using variable-temperature atomic pair distribution function analysis, we study the local atomic structure of the ``dual'' heavy fermion liquid $\mathrm{U}{\mathrm{Pt}}_{2}{\mathrm{Si}}_{2}$, which exhibits antiferromagnetism consistent with localized $5f$-electron states and transport properties characteristic to itinerant $5f$-``$spd$'' hybridized electron systems. We show that $\mathrm{U}{\mathrm{Pt}}_{2}{\mathrm{Si}}_{2}$ exhibits periodic lattice distortions (PLDs) involving both uranium and platinum atoms that are characteristic to three-dimensional charge density waves. The temperature evolution of the PLDs tracks that of the transport and magnetic properties, suggesting the presence of little-known $5f$-electron-lattice interactions. We argue that PLDs in heavy fermion liquids in general, and in particular in $\mathrm{U}{\mathrm{Pt}}_{2}{\mathrm{Si}}_{2}$, appear as new degrees of freedom that entangle competing electronic states and, as such, must be accounted for when their rich physics is considered.

Chemical compression and ferroic orders in La substituted BiFeO3

Chemical compression effects on the ferroic orders in La substituted $\mathrm{BiFe}{\mathrm{O}}_{3}$ are studied by atomic pair distribution function analysis and structure modeling. While rhombohedral $\mathrm{BiFe}{\mathrm{O}}_{3}$ exhibits ferroelectricity and antiferromagnetism (AF) with a cycloidal Fe spin arrangement leading to zero magnetization, La substituted $\mathrm{BiFe}{\mathrm{O}}_{3}$ exhibits a reduced lattice polarization, strengthened AF order, and an apparently suppressed spin cycloid leading to nonzero magnetization. The observed changes in the ferroic orders arise from the chemical compression induced changes in the octahedral rotation and ferroelectric displacement of Bi atoms, which appear as lattice degrees of freedom entangling the electronic and magnetic orders in $\mathrm{BiFe}{\mathrm{O}}_{3}$.

Crystallization characteristics in Co-based magnetic amorphous nanocomposites

Examination of the devitrification behavior of amorphous melt spun Co(78-x)Fe2MnxB14Si2Nb4 (x = 0.5 and 6.0%) alloys has been undertaken. These materials offer promising properties for use in high-power electronic systems where the microstructural evolution from processing is critical to developing permeability engineered, low-loss components. Transmission electron microscopy (TEM) and atom probe tomography (APT) reveal the precipitation of crystallites in the as-cast Mn 0.5% alloy, while such crystallites were absent in the as-cast Mn 6.0% alloy. After annealing at 400 °C for 10 min and 2 h, both alloys exhibit Co-rich nanocrystallites that are ≈3–5 nm in diameter while exhibiting little change in their crystal structure, morphology, and/or chemical partitioning behavior between each alloy or between the two annealing times. Short range ordering measurements determined from the atomic pair distribution function by electron diffraction reveals a modification of the second nearest neighbor bonding in these crystallites that is explained by the metastable incorporation of Fe into the crystallite. TEM and X-ray diffraction analyses reveal that annealing at longer times at 400 °C, i.e., for 3 h and 6 h for Mn 0.5% and Mn 6.0% respectively, results in a secondary precipitation of a transition metal (TM) boride phase, TM23B6, which is hundreds of nanometers in size.

Structural Analysis and Intrinsic Enzyme Mimicking Activities of Ligand‐Free PtAg Nanoalloys (Small 19/2023)

Ligand-Free PtAg Nanoalloys In article number 2206772, Indranath Chakraborty and co-workers use the atomic pair-distribution function combined with powder X-ray diffraction and transmission electron microscopy for structural analysis of ligand-free PtAg nanoclusters (NCs). They further investigate the intrinsic enzyme-mimicking properties of these ligand-free NCs and explored the mechanistic details.

Extended q-Range X-Ray Scattering Reveals High-Resolution Structural Details of Biomacromolecules in Aqueous Solutions.

We communicate a feasibility study for high-resolution structural characterization of biomacromolecules in aqueous solution from X-ray scattering experiments measured over a range of scattering vectors (q) that is approximately two orders of magnitude wider than used previously for such systems. Scattering data with such an extended q-range enables the recovery of the underlying real-space atomic pair distribution function, which facilitates structure determination. We demonstrate the potential of this method for biomacromolecules using several types of cyclodextrins (CD) as model systems. We successfully identified deviations of the tilting angles for the glycosidic units in CDs in aqueous solutions relative to their values in the crystalline forms of these molecules. Such level of structural detail is inaccessible from standard small angle scattering measurements. Our results call for further exploration of ultra-wide-angle X-ray scattering measurements for biomacromolecules.

Pair distribution function analysis of nano-object assemblies

The atomic pair distribution function (aPDF) analysis technique, also known as the total scattering method, which considers both Bragg and diffuse scattering, has been used extensively to probe local atomic arrangements in crystalline and disordered materials. In contrast, there have been limited applications of the PDF in self-assembled nanomaterials, which represent a class of materials built from nanoscale objects, such as nano-colloids, micelles and proteins. As distinguished from atoms, nano-objects have polydispersity in size and shape, and such form-factor effects complicate the application of PDF analysis to nano-systems. Herein, the application of the PDF is extended to spherical nano-object assemblies and the formulae for the nano-PDF (nPDF) are derived, showing some differences from the aPDF. By numerical simulations, the properties of the nPDF (peak broadening and pattern profile) are studied systematically as a function of structural features, such as nano-object parameters (size and size polydispersity) and assembly structural features (size, shape, structure type and lattice disorder), and of data processing parameters (q cut-off and `missing' data in ultra-small-angle regions). The nPDF analysis method is found to provide an effective route to revealing not only nanoscale but also mesoscale structural properties, for example the morphology of a nano-assembly.

Structural and Thermodynamic Behaviors of CumAgn (m + n = 144–147) Nanoalloys during Cooling: Implications for Nanoparticle Structure Control

Molecular dynamics simulations are performed to explore the structural and thermodynamic changes of four nanoalloys with the addition or removal of one atom during cooling. The simulation results reveal that there are significant differences in the structural diagrams of the nanoalloys from potential energy, free energy, and entropy as well as visually atomic packing images and pair distribution functions. There are apparent effects of compositions and sizes on the structural transitions as well as the transition process. The results also show that during the cooling processes, there are multi-structural transition processes for the nanoalloys having different compositions, and most of the nanoalloys show a transition from a liquid state to a core–shell metastable packing structure and then to an Ih packing structure. The compositions and atom numbers as well as the shape also affect the thermodynamic quantities. The findings contribute to the understanding of fundamental issues involved in alloying between Cu and Ag metals and are important for the precise control of the preparation of Cu–Ag nanoalloys with specific structures.

Recognizing the Minimum Structural Units Driving the Crystallization of SAPO-34 in a Top-Down Process.

Recognizing the structure and nature of the nuclei for zeolites crystallization on an atomic level is of great importance, which can provide guidance on the control of crystallization kinetics and the rational synthesis of zeolites. However, it remains a long-standing challenge due to the difficulty in characterization of amorphous precursor with limited crystal nuclei. Herein, a top-down synthesis system was designed for SAPO-34 molecular sieve and well investigated. A clear precursor solution with abundant SAPO-34 crystal nuclei was obtained under a depolymerization-dominant condition. The species in the liquid precursor were identified by FT-ICR MS, solid-state MAS NMR and atomic pair distribution function analyses. In combination with various designed experiments, it is revealed that both the formation of small species containing Si-O-Al bonds and reaching a certain concentration, is crucial for driving the crystallization of SAPO-34, rather than structural units with specific spatial conformation. This work provides an important understanding on the (pre)nucleation of SAPO-34 and sheds light on the synthesis control of SAPO molecular sieves.

Structural Analysis and Intrinsic Enzyme Mimicking Activities of Ligand-Free PtAg Nanoalloys.

Nanozymes are nanomaterials with biocatalytic properties under physiological conditions and are one class of artificial enzymes to overcome the high cost and low stability of natural enzymes. However, surface ligands on nanomaterials will decrease the catalytic activity of the nanozymes by blocking the active sites. To address this limitation, ligand-free PtAg nanoclusters (NCs) are synthesized and applied as nanozymes for various enzyme-mimicking reactions. By taking advantage of the mutual interaction of zeolitic imidazolate frameworks (ZIF-8) and Pt precursors, a good dispersion of PtAg bimetal NCs with a diameter of 1.78±0.1nm is achieved with ZIF-8 as a template. The incorporation of PtAgNCs in the voids of ZIF-8 is confirmed with structural analysis using the atomic pair-distribution function and powder X-ray diffraction. Importantly, the PtAgNCs present good catalytic activity for various enzyme-mimicking reactions, including peroxidase-/catalase- and oxidase-like reactions. Further, this work compares the catalytic activity between PtAg NCs and PtAg nanoparticles with different compositions and finds that these two nanozymes present a converse dependency of Ag-loading on their activity. This study contributes to the field of nanozymes and presents a potential option to prepare ligand-free bimetal biocatalysts with sizes in the nanocluster regime.

A spherical harmonics method for processing anisotropic X-ray atomic pair distribution functions

In this work, a general spherical harmonics method for the extraction of anisotropic pair distribution functions (PDFs) is described. In the structural study of functional crystallized materials, there is an urgent need for investigation of local structures under the application of external stimuli, such as an electric field and stress. A well established technique for local structural studies is PDF analysis, but the extraction of X-ray PDF data is usually based on angular integrations of isotropic X-ray structure functions, which is no longer valid for the anisotropic responses of materials under orientation-dependent stimuli. Therefore, an advanced spherical harmonics method has been developed, to transform 2D X-ray total-scattering data into anisotropic PDF data on the basis of the 3D diffraction geometry and a Fourier transform. The electric-field-induced local structural change in PbZr0.54Ti0.46O3 ceramics is presented to demonstrate the effectiveness of this method.

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.