Oxide Ion Conductivity, Proton Conductivity, and Phase Transitions in Perovskite-Derived Ba Sr YGaO 0 ≤ ≤ 3 Materials.

We report the synthesis, structural characterization, and oxide ion and proton conductivities of the perovskite-related Ba Sr YGaO family. Single-phase samples are prepared for 0 ≤ ≤ 3 and show a complex structural evolution from 2/ to 2 space groups with an increase in . For 1.

Oxide Ion and Proton Conductivity in a Family of Highly Oxygen-Deficient Perovskite Derivatives.

Functional oxides showing high ionic conductivity have many important technological applications. We report oxide ion and proton conductivity in a family of perovskite-related compounds of the general formula AOhTdO, where Oh is an octahedrally coordinated metal ion and Td is a tetrahedrally coordinated metal ion. The high tetrahedral content in these ABO compositions relative to that in the perovskite ABO or brownmillerite ABO structures leads to tetrahedra with only three of their four vertices connected in the polyhedral framework, imparting a potential low-energy mechanism for O migration.

Detecting Framework Distortions Predicted by Hybrid-DFT: An Opportunity to Improve the M1 Catalyst.

Scanning transmission electron microscopy imaging of the MoVNbTe-oxide used as a catalyst for oxidative dehydrogenation and partial oxidation establishes anisotropic scattering projections of atom columns composed of Mo and V atoms which image the catalytically active S2 site and were predicted to be distorted by hybrid density functional theory calculations. These distortions of the S2 sites toward empty hexagonal channels created by the removal of [TeO] entities experimentally corroborate that controlled partial occupancy of (TeO) chains in the hexagonal channels of the MoVNbO-framework provides a means to introduce polarons and thereby increase the catalytic reactivity and selectivity of this catalyst.

Pressure-induced assemblies and structures of graphitic-carbon sheet encapsulated Au nanoparticles.

A novel strategy of using hydrostatic pressures to synthesize gold-carbon (Au-C) nanohybrid materials is explored. The stable face-centered-cubic (fcc) Au undergoes a structural phase transition to a mixture of primitive orthorhombic and cubic phases as the carbon phase acquires a highly ordered onion-like carbon (OLC) structure which encapsulates the Au nanoparticles, thereby exerting an additional pressure. Increasing the pressure results in a one dimensional (1-D) chain-like structure with the primitive cubic Au nanoparticles contained in an amorphous carbon matrix.

Probing Compositional Order in Atomic Columns: STEM Simulations Beyond the Virtual Crystal Approximation.

Taking advantage of recent advances in parallel computing, we studied compositional disorder along metal-oxygen atomic columns in a complex Mo,V-oxide bronze using multislice frozen-phonon calculations. Commonly, the virtual crystal approximation (VCA) is used to model compositional disorder at crystallographic sites in a unit cell for a number of different theoretical and experimental techniques. In the VCA, a weighted linear sum of atomic properties is used to approximate the model structure.

High-Pressure Phase Transitions of Morphologically Distinct ZnSnO Nanostructures.

Many aspects of nanostructured materials at high pressures are still unexplored. We present here, high-pressure structural behavior of two ZnSnO nanomaterials with inverse spinel type, one a particle with size of ∼7 nm [zero dimensional (0-D)] and the other with a chain-like [one dimensional (1-D)] morphology. We performed in situ micro-Raman and synchrotron X-ray diffraction measurements and observed that the cation disordering of the 0-D nanoparticle is preserved up to ∼40 GPa, suppressing the reported martensitic phase transformation.

Tweaking the Interplay among Galvanic Exchange, Oxidative Etching, and Seed-Mediated Deposition toward Architectural Control of Multimetallic Nanoelectrocatalysts.

Nanoscale galvanic exchange confined by metallic nanoparticles is an intriguing structure-remodeling process that transforms geometrically simple solid nanoparticles into multimetallic hollow nanoparticles with increased structural complexity and compositional diversity. Using liquid polyols with intrinsic reducing capabilities as the reaction medium for nanoparticle-templated galvanic exchange represents an interesting paradigm shift, allowing us to interface galvanic exchange with oxidative etching and seed-mediated deposition without introducing any additional oxidizing or reducing agents. By kinetically maneuvering the interplay among galvanic Cu-Pt exchange, oxidative Cu etching, and seed-mediated Pt deposition, we have been able to selectively transform AuCu alloy nanoparticles into two architecturally distinct multimetallic heteronanostructures, namely, Au-Pt alloy skin-covered spongy nanoparticles and Pt nanodendrite-covered hollow nanoparticles, both of which exhibit unique structural features highly desirable for high-performance electrocatalysis.

Pressure-driven phase transitions and reduction of dimensionality in 2D silicon nanosheets.

In-situ high-pressure synchrotron X-ray powder diffraction studies up to 21 GPa of CVD-grown silicon 2D-nanosheets establish that the structural phase transitions depend on size and shape. For sizes between 9.3(7) nm and 15.

Multi-slice frozen phonon simulations of high-angle annular dark field scanning transmission electron microscopy images of the structurally and compositionally complex Mo-V-Nb-Te oxide catalyst.

We report frozen phonon multi-slice image simulations for the complex oxidation catalyst M1. Quantitative analysis of the simulations suggests that the detailed order of the cations along the electron propagation direction in a [001] zone axis orientation can lead to different high-angle annular dark field signals from atomic columns with identical composition. The annular dark field signal varies linearly with atomic percent V, and the spread of intensities due to the atomic species order is of similar magnitude to the intensity difference due to ± 5% V.

Ethylene Epoxidation Catalyzed by Ag Nanoparticles on Ag-LSX Zeolites formed by Pressure- and Temperature-Induced Auto-Reduction.

Ag -Exchanged LSX (Ag-LSX: Ag Al Si O ⋅n H O), a large pore low silica analogue (Si/Al=1.0) of faujasite, was prepared and post-synthetically modified using pressure and temperature in the presence of various pore-penetrating fluids. Using high-resolution synchrotron X-ray powder and single crystal diffraction we derive structural models of the as-prepared and post-synthetically modified Ag-LSX materials.

Gel permeation chromatography as a multifunctional processor for nanocrystal purification and on-column ligand exchange chemistry.

This article illustrates the use of gel permeation chromatography (GPC, organic-phase size exclusion chromatography) to separate nanocrystals from weakly-bound small molecules, including solvent, on the basis of size. A variety of colloidal inorganic nanocrystals of different size, shape, composition, and surface termination are shown to yield purified samples with greatly reduced impurity concentrations. Additionally, the method is shown to be useful in achieving a change of solvent without requiring precipitation of the nanocrystals.

Facet Control of Gold Nanorods.

While great success has been achieved in fine-tuning the aspect ratios and thereby the plasmon resonances of cylindrical Au nanorods, facet control with atomic level precision on the highly curved nanorod surfaces has long been a significantly more challenging task. The intrinsic structural complexity and lack of precise facet control of the nanorod surfaces remain the major obstacles for the atomic-level elucidation of the structure-property relationships that underpin the intriguing catalytic performance of Au nanorods. Here we demonstrate that the facets of single-crystalline Au nanorods can be precisely tailored using cuprous ions and cetyltrimethylammonium bromide as a unique pair of surface capping competitors to guide the particle geometry evolution during nanorod overgrowth.

High-pressure and high-temperature transformation of Pb(II)-natrolite to Pb(II)-lawsonite.

We report on high-pressure and high-temperature chemical transformations of Pb(2+)-exchanged natrolite (Pb-NAT, Pb8Al16Si24O80·16H2O) using a combination of in situ synchrotron X-ray powder diffraction and ex situ HAADF-STEM real space imaging. Three high-pressure polymorphs of natrolites (Pb-NAT-I, II, III) are observed via step-wise pressure-induced hydrations (PIH) up to 4.5 GPa, during which the number of H2O molecules located inside the natrolite channel increases from 16 to 40 H2O per unit-cell.

Pressure-Induced Amorphization of Small Pore Zeolites-the Role of Cation-H2O Topology and Anti-glass Formation.

Systematic studies of pressure-induced amorphization of natrolites (PIA) containing monovalent extra-framework cations (EFC) Li(+), Na(+), K(+), Rb(+), Cs(+) allow us to assess the role of two different EFC-H2O configurations within the pores of a zeolite: one arrangement has H2O molecules (NATI) and the other the EFC (NATII) in closer proximity to the aluminosilicate framework. We show that NATI materials have a lower onset pressure of PIA than the NATII materials containing Rb and Cs as EFC. The onset pressure of amorphization (PA) of NATII materials increases linearly with the size of the EFC, whereas their initial bulk moduli (P1 phase) decrease linearly.

Pressure-induced metathesis reaction to sequester Cs.

We report here a pressure-driven metathesis reaction where Ag-exchanged natrolite (Ag16Al16Si24O80·16H2O, Ag-NAT) is pressurized in an aqueous CsI solution, resulting in the exchange of Ag(+) by Cs(+) in the natrolite framework forming Cs16Al16Si24O80·16H2O (Cs-NAT-I) and, above 0.5 GPa, its high-pressure polymorph (Cs-NAT-II). During the initial cation exchange, the precipitation of AgI occurs.

Irreversible xenon insertion into a small-pore zeolite at moderate pressures and temperatures.

Pressure drastically alters the chemical and physical properties of materials and allows structural phase transitions and chemical reactions to occur that defy much of our understanding gained under ambient conditions. Particularly exciting is the high-pressure chemistry of xenon, which is known to react with hydrogen and ice at high pressures and form stable compounds. Here, we show that Ag16Al16Si24O8·16H2O (Ag-natrolite) irreversibly inserts xenon into its micropores at 1.

Tunable plasmonic nanoparticles with catalytically active high-index facets.

Noble metal nanoparticles have been of tremendous interest due to their intriguing size- and shape-dependent plasmonic and catalytic properties. Combining tunable plasmon resonances with superior catalytic activities on the same metallic nanoparticle, however, has long been challenging because nanoplasmonics and nanocatalysis typically require nanoparticles in two drastically different size regimes. Here, we demonstrate that creation of high-index facets on subwavelength metallic nanoparticles provides a unique approach to the integration of desired plasmonic and catalytic properties on the same nanoparticle.

Multislice frozen phonon high angle annular dark-field image simulation study of Mo-V-Nb-Te-O complex oxidation catalyst "M1".

Multislice frozen phonon calculations were performed on a model structure of a complex oxide which has potential use as an ammoxidation catalyst. The structure has 11 cation sites in the framework, several of which exhibit mixed Mo/V substitution. In this paper the sensitivity of high-angle annular dark-field (HAADF) imaging to partial substitution of V for Mo in this structure is reported.

Gold clusters showing pentagonal atomic arrays revealed by aberration-corrected scanning transmission electron microscopy.

In this work we present the analysis by aberration corrected electron microscopy of the formation of gold clusters based on the proton irradiation of larger nanoparticles (NP). Pentagonal arrays have been observed and energetic calculations have been performed in order to prove the stability of these materials.

Insights into the capping and structure of MoS(2) nanotubes as revealed by aberration-corrected STEM.

Aberration-corrected electron microscopy (STEM-HAADF) has been used for the first time to understand the capping, nature and structure of the MoS(2) nanotubes. The MoS(2) nanotubes that have been obtained have various unusual faceted caps presumably arising from the presence of topological defects. A detailed study of the capping of the nanotubes, along with identification that the MoS(2) nanotubes are of the zigzag type have been carried out using both experimental and simulated STEM images.

Atomic-level imaging of Mo-V-O complex oxide phase intergrowth, grain boundaries, and defects using HAADF-STEM.

In this work, we structurally characterize defects, grain boundaries, and intergrowth phases observed in various Mo-V-O materials using aberration-corrected high-angle annular dark-field (HAADF) imaging within a scanning transmission electron microscope (STEM). Atomic-level imaging of these preparations clearly shows domains of the orthorhombic M1-type phase intergrown with the trigonal phase. Idealized models based on HAADF imaging indicate that atomic-scale registry at the domain boundaries can be seamless with several possible trigonal and M1-type unit cell orientation relationships.

New catalytic liquid-phase ammoxidation approach to the preparation of niacin (vitamin B3).

New highly dispersed bimetallic nanoscale catalysts based on rhenium combined with antimony or bismuth have been shown to be highly effective for the ammoxidation of 3-picoline to nicotinonitrile (precursor for vitamin B3) under mild conditions in the liquid phase.

Synthesis of orthorhombic Mo-V-Sb oxide species by assembly of pentagonal Mo6O21 polyoxometalate building blocks.

Mix and match: The pentagonal [Mo(6)O(21)](n-) polyoxomolybdate building block assembles with other sources of Mo, V, and Sb ions to form an orthorhombic Mo-V-Sb oxide. The first single-crystal X-ray analysis of an orthorhombic Mo-V-based oxide, a promising catalyst for light alkane selective oxidation known as the "M1 phase", revealed the structure of the compound.

Aberration-corrected STEM investigation of the M2 phase of MoVNbTeO selective oxidation catalyst.

The 'M2' phase of the oxidation catalyst MoVNbTeO was studied with an aberration-corrected STEM using HAADF imaging, and three 60 degrees twin orientations were identified. Comparisons between the experimental HAADF images and image simulations suggest that the there are two different Te sites, as has been previously reported; however, there are differences between the structure proposed in DeSanto et al. (2004) Z.