X-ray Atomic Pair Distribution Function Research Articles

Structure of nanocrystalline Ti3C2 MXene using atomic pair distribution function.

The structures of nanocrystalline pristine, potassium hydroxide and sodium acetate intercalated new two-dimensional materials Ti3C2 MXenes were studied using the x-ray atomic pair distribution function technique. Pristine MXene has a hexagonal structure with a=b=3.0505(5) Å, c=19.86(2) Å (S.G. P63/mmc No.194). Both hydroxyl and fluoride terminating species are present. The intercalation of K+ or Na+ ions expands the Ti3C2 layers perpendicular to the planes but shrinks the in-plane a and b lattice parameters.

Pair distribution function computed tomography

An emerging theme of modern composites and devices is the coupling of nanostructural properties of materials with their targeted arrangement at the microscale. Of the imaging techniques developed that provide insight into such designer materials and devices, those based on diffraction are particularly useful. However, to date, these have been heavily restrictive, providing information only on materials that exhibit high crystallographic ordering. Here we describe a method that uses a combination of X-ray atomic pair distribution function analysis and computed tomography to overcome this limitation. It allows the structure of nanocrystalline and amorphous materials to be identified, quantified and mapped. We demonstrate the method with a phantom object and subsequently apply it to resolving, in situ, the physicochemical states of a heterogeneous catalyst system. The method may have potential impact across a range of disciplines from materials science, biomaterials, geology, environmental science, palaeontology and cultural heritage to health.

Confirmation of disordered structure of ultrasmall CdSe nanoparticles from X-ray atomic pair distribution function analysis

The atomic pair distribution function (PDF) analysis of X-ray powder diffraction data has been used to study the structure of small and ultra-small CdSe nanoparticles. A method is described that uses a wurtzite and zinc-blende mixed phase model to account for stacking faults in CdSe particles. The mixed-phase model successfully describes the structure of nanoparticles larger than 2 nm yielding a stacking fault density of about 30%. However, for ultrasmall nanoparticles smaller than 2 nm, the models cannot fit the experimental PDF showing that the structure is significantly modified from that of larger particles and the bulk. The observation of a significant change in the average structure at ultra-small size is likely to explain the unusual properties of the ultrasmall particles such as their white light emitting ability.

Local Structure Analysis of Bi2WO6

A local structure analysis of Bi2WO6 was performed by high-energy X-ray atomic pair-distribution function (PDF) analysis. We found a deviation between the local and average structures owing to the different coherence lengths between the Bi2O2 and WO6 layers. Bi atoms were displaced toward the b-axis of the orthorhombic Pca21 structure. The local off-center shift of Bi atoms coupled with the thermal factor but not with the average structure and thus was neglected. The coherence length of the Bi2O2 layer increased with increasing temperature and spread in the whole crystal when the average structure changed from the Pca21 structure to the Aba2 structure.

Local Structure Analysis of Bi2WO6

A local structure analysis of Bi2WO6 was performed by high-energy X-ray atomic pair-distribution function (PDF) analysis. We found a deviation between the local and average structures owing to the different coherence lengths between the Bi2O2 and WO6 layers. Bi atoms were displaced toward the b-axis of the orthorhombic Pca21 structure. The local off-center shift of Bi atoms coupled with the thermal factor but not with the average structure and thus was neglected. The coherence length of the Bi2O2 layer increased with increasing temperature and spread in the whole crystal when the average structure changed from the Pca21 structure to the Aba2 structure.

Diverse Structural and Magnetic Properties of Differently Prepared MnAs Nanoparticles

Discrete nanoparticles of MnAs with distinct magnetostructural properties have been prepared by small modifications of solution-phase arrested precipitation reactions. Rietveld and X-ray atomic pair distribution function based approaches were used to explore the evolution of the structure of the samples with temperature, and these data were compared to the magnetic response measured with ac susceptibility. Relative to a bulk standard, one type of MnAs nanoparticles was found to demonstrate similar but smaller structural transitions and corresponding magnetic changes. However, both magnetic and structural transitions in the second type of nanoparticles are strongly suppressed.

Size, Shape, and Internal Atomic Ordering of Nanocrystals by Atomic Pair Distribution Functions: A Comparative Study of γ-Fe2O3 Nanosized Spheres and Tetrapods

Due to their limited length of structural coherence nanocrystalline materials show very diffuse powder X-ray diffraction patterns that are difficult to interpret unambiguously. We demonstrate that a combination of high-energy X-ray powder diffraction and atomic pair distribution function analysis can be used to both assess the geometry (i.e., size and shape) and determine the internal atomic ordering of nanocrystalline materials in a straightforward way. As an example we consider cubic gamma-Fe(2)O(3) nanosized crystals shaped as spheres and tetrapods.

Atomic-Scale Structure of Biogenic Materials by Total X-ray Diffraction: A Study of Bacterial and Fungal MnOx

Biogenic materials are produced by microorganisms and are typically found in a nanophase state. As such, they are difficult to characterize structurally. In this report, we demonstrate how high-energy X-ray diffraction and atomic pair distribution function analysis can be used to determine the atomic-scale structures of MnO(x) produced by bacteria and fungi. These structures are well-defined, periodic, and species-specific, built of Mn-O(6) octahedra forming birnessite-type layers and todorokite-type tunnels, respectively. The inherent structural diversity of biogenic material may offer opportunities for practical applications.

X-Ray pair distribution function analysis of a metakaolin-based, KAlSi2O6·5.5H2O inorganic polymer (geopolymer)

The atomic structure of geopolymers is often described as amorphous with a local structure that is equivalent to that of crystalline zeolites. However, this structural relationship has never been quantified beyond a first-nearest-neighbor bonding environment. In this study, the short to medium range (∼1 nm) structural order of metakaolin-based KAlSi2O6·5.5H2O geopolymer was quantified and compared to zeolitic tetragonal leucite (KAlSi2O6) using the X-ray atomic pair distribution function technique. Unheated KAlSi2O6·5.5H2O was found to be structurally similar to leucite out to a length of ∼8 A, but had increased medium range disorder over the 4.5 A 300 °C, changes in the short to medium range structure were observed due to dehydration and removal of chemically bound water. Crystallization of leucite occurred in samples heated beyond 1050 °C. Refinements of a leucite model against the PDF data for geopolymer heated to 1100 °C for 24 h yielded a good fit.

Atomic-Scale Structure of Nanosized Titania and Titanate: Particles, Wires, and Tubes

The atomic-scale structure of nanosized “TiO2-type” materials of different morphologies, including particles, wires. and tubes, has been determined by total X-ray diffraction and atomic pair distribution function analysis. Atoms in dense-filled materials such as nanoparticles and nanowires are found to form a three-dimensional network of TiO6 octahedra, similar to that occurring in bulk TiO2. Atoms in hollow materials such as nanotubes are arranged in corrugated layers of TiO6 octahedra. The study calls attention to the often overlooked fact that a materialʼs morphology and atomic ordering may be strongly correlated at the nanoscale.

Structure of nanosized materials by high-energy X-ray diffraction: study of titanate nanotubes

High-energy X-ray diffraction and atomic Pair Distribution Function analysis are employed to determine the atomic-scale structure of titanate nanotubes. It is found that the nanotube walls are built of layers of Ti–O6 octahedra simular to those observed in crystalline layered titanates. In the nanotubes, however, the layers are bent and not stacked in perfect registry as in the crystal.

Three-dimensional structure of CdX (X=Se,Te) nanocrystals by total x-ray diffraction

The three-dimensional structure of oleic acid-capped CdSe and thiol-capped CdTe nanocrystals used as quantum dots has been determined by total synchrotron radiation x-ray diffraction and atomic pair distribution function analysis. Both CdSe and CdTe are found to exhibit the zinc-blende-type atomic ordering. It is only slightly distorted in CdSe implying the presence of nanosize domains and very heavily distorted in CdTe due to the presence of distinct core-shell regions. The results well demonstrate the great potential of the experimental approach and thus encourage its wider application in quantum dot research.

PbZr1−xTixO3by soft synthesis: Structural aspects

The structural aspects of a soft synthetic route employed to obtain fine crystallite $\mathrm{Pb}{\mathrm{Zr}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{x}{\mathrm{O}}_{3}$ $(x=0,0.5,1)$ powders are revealed by total x-ray diffraction and atomic pair distribution function analysis. It is found that the atomic-scale structure of the intermediate, highly disordered phase the route passes through resembles but is not exactly of the targeted, perovskite-type structure. It is suggested that future synthesis efforts are directed toward closing the observed ``structure gap'' as much as possible.

Titania Polymorphs by Soft Chemistry: Is There a Common Structural Pattern?

The structural aspects of a soft chemical route1 employed to obtain nitrogen-doped brookite, rutile, or anatase fine crystallite powders are revealed by total X-ray diffraction and atomic pair distribution function analysis. It is found that the route first passes through a heavily disordered phase consisting of nanosize layers of TiO6 octahedra, similar to those occurring in the lepidocrocite-type structure. That phase is then transformed into a particular titania polymorph by rearranging the layers in a controlled way. The lepidocrocite-type structure thus again proves to be a very useful template in the soft chemistry of titania.

Atomic-scale structure of nanocrystallineCeO2–ZrO2 oxides by total x-ray diffraction and pair distribution function analysis

Total x-ray diffraction and atomic pair distribution function analysishave been used to determine the atomic ordering in nanocrystalline(∼1.5 nm insize) CeO2–ZrO2 prepared by a sol–gel route. Experimental data show that the oxides are a structurally andchemically inhomogeneous mixture of nanoscale domains with cubic-type andmonoclinic-type atomic ordering, predominantly occupied by Ce and Zr atomicspecies, respectively. The study is another demonstration of the great potential ofnon-traditional crystallography in studying the structure of nanocrystalline materials.

Atomic-Scale Structure of Nanocrystals by High-Energy X-ray Diffraction and Atomic Pair Distribution Function Analysis: Study of FexPd100-x (x = 0, 26, 28, 48) Nanoparticles

Knowledge of the atomic-scale structure is an important prerequisite to understanding and predicting properties of materials. With bulk crystals it is routinely obtained by X-ray diffraction. With nanocrystals, however, traditional X-ray crystallography fails because of their substantially limited length of structural coherence. Here we illustrate, step by step, how a nontraditional approach involving high-energy X-ray diffraction and atomic pair distribution function analysis is applied to determine the atomic-scale structure of a typical nanocrystalline materialFexPd100-x (x = 0, 26, 28, 48) nanoparticles exhibiting useful magnetic properties.

D014 Three-dimensional structure of nanophase materials from high-energy X-ray diffraction and atomic pair distribution function analysis

D014 Three-dimensional structure of nanophase materials from high-energy X-ray diffraction and atomic pair distribution function analysis

Crystallization process of ferroelectric Bi4Ti3O12 from amorphous state

A glass sample with the composition Bi4Ti3O12 (BiT) was prepared by the conventional quenched-melt technique. The as-quenched sample was confirmed to be amorphous by synchrotron x-ray diffraction measurements. Scanning electron microscopy showed no sign of coarse grain growth. The crystallization temperature was determined by differential thermal analysis. Amorphous BiT first crystallized at Tcryst1 to a metastable crystalline phase and then transformed irreversibly to the stable crystalline phase at Tcryst2. We also established the structural relationship between the amorphous and the crystalline state by high-energy x-ray diffraction and atomic pair distribution function analyses.

Structure of nanocrystalline GaN from X-ray diffraction, Rietveld and atomic pair distribution function analyses

The three-dimensional structure of nanocrystalline GaN has been studied by X-ray diffraction, Rietveld and atomic pair distribution function (PDF) analyses. The material is of very limited structural coherence, yet possess a well-defined atomic arrangement resembling the wurtzite structure. The study demonstrates the great power of X-ray diffraction and the PDF approach in determining the three-dimensional structure of nanocrystalline materials.

Structure of Nanocrystalline Alkali Metal Manganese Oxides by the Atomic Pair Distribution Function Technique

The atomic scale structures of two nanocrystalline K−Li−Mn−O−I materials obtained through Chimie Douce route in aqueous and acetone solutions have been determined using X-ray diffraction and atomic Pair Distribution Function technique. Both samples have been found to possess a layered-type structure, where the layers are made of edge-shared MnO6 octahedra. With the sample prepared in aqueous solution, the layers are well separated and the interlayer space is occupied by both Li and K atoms. With the sample prepared in acetone solution the Mn−O layers are not so well separated and encapsulate mostly Li atoms. This material exhibits some Li/Mn substitutional disorder as well. The new structural information has been used to explain the electrochemical behavior of the two nanocrystalline materials. Some methodological aspects of the atomic pair distribution function technique and its applicability to study the structure of crystalline and nanocrystalline materials have been discussed as well.