A New Solid-State Proton Conductor: The Salt Hydrate Based on Imidazolium and 12-Tungstophosphate.

We report the structure and charge transport properties of a novel solid-state proton conductor obtained by acid-base chemistry via proton transfer from 12-tungstophosphoric acid to imidazole. The resulting material (henceforth named ImidWP) is a solid salt hydrate that, at room temperature, includes four water molecules per structural unit. To our knowledge, this is the first attempt to tune the properties of a heteropolyacid-based solid-state proton conductor by means of a mixture of water and imidazole, interpolating between water-based and ionic liquid-based proton conductors of high thermal and electrochemical stability.

The Relative Thermodynamic Stability of Diamond and Graphite.

Recent density-functional theory (DFT) calculations raised the possibility that diamond could be degenerate with graphite at very low temperatures. Through high-accuracy calorimetric experiments closing gaps in available data, we reinvestigate the relative thermodynamic stability of diamond and graphite. For T<400 K, graphite is always more stable than diamond at ambient pressure.

ABINIT: Overview and focus on selected capabilities.

abinit is probably the first electronic-structure package to have been released under an open-source license about 20 years ago. It implements density functional theory, density-functional perturbation theory (DFPT), many-body perturbation theory (GW approximation and Bethe-Salpeter equation), and more specific or advanced formalisms, such as dynamical mean-field theory (DMFT) and the "temperature-dependent effective potential" approach for anharmonic effects. Relying on planewaves for the representation of wavefunctions, density, and other space-dependent quantities, with pseudopotentials or projector-augmented waves (PAWs), it is well suited for the study of periodic materials, although nanostructures and molecules can be treated with the supercell technique.

Solid-state nuclear magnetic resonance investigation of synthetic phlogopite and lepidolite samples.

In the present work, our aim is to decipher the cationic ordering in the octahedral and tetrahedral sheets of two Al-rich synthetic materials, namely, phlogopites of nominal composition K(Mg Al )[Al Si O ](OH) F and lepidolites in the system trilithionite-polylithionite with composition K (Li Al )[Al Si O ](OH) F , by directly probing the aluminium distribution through Al and O magic-angle spinning, multiple-quantum magic-angle spinning, and Al- Al double-quantum single-quantum nuclear magnetic resonance (NMR) experiments. Notably, Al- Al double-quantum single-quantum magic-angle spinning NMR spectra, recorded at 9.34 and/or 20.

A long-chain protic ionic liquid inside silica nanopores: enhanced proton mobility due to efficient self-assembly and decoupled proton transport.

We report enhanced protonic and ionic dynamics in an imidazole/protic ionic liquid mixture confined within the nanopores of silica particles. The ionic liquid is 1-octylimidazolium bis(trifluoromethanesulfonyl)imide ([HC8Im][TFSI]), while the silica particles are microsized and characterized by internal well connected nanopores. We demonstrate that the addition of imidazole is crucial to promote a proton motion decoupled from molecular diffusion, which occurs due to the establishment of new N-HN hydrogen bonds and fast proton exchange events in the ionic domains, as evidenced by both infrared and 1H NMR spectroscopy.

Te NMR Probes of Tellurium Oxide Crystals: Shielding-Structure Correlations.

The local environments around tellurium atoms in a series of tellurium oxide crystals were probed by Te solid-state NMR spectroscopy. Crystals with distinct TeO units (n from 3 to 6), including NaTeO, α-TeO and γ-TeO, TeO(PO), KLaTeO, BaZnTeO, and CsYTeO were studied. The latter four were synthesized through a solid-state process.

Computation of NMR observables: Consequences of projector-augmented wave sphere overlap.

The assumptions underlying the popular projector-augmented wave (PAW) method of computing electronic structure in solids are examined, with primary attention to the computation of NMR observables. In particular, the assumption of non-overlapping PAW spheres is studied, and it is shown that when the spheres do overlap, the errors may be significant and furthermore are of unpredictable sign. Examples are provided by comparing PAW-based calculations with and without overlapping spheres, with the highly accurate all-electron linear augmented wave method.

Relationships between elastic anisotropy and thermal expansion in AMoO materials.

We report calculated elastic tensors, axial Grüneisen parameters, and thermal stress distributions in AlMoO, ZrMgMoO, ScMoO, and YMoO, a series of isomorphic materials for which the coefficients of thermal expansion range from low-positive to negative. Thermal stress in polycrystalline materials arises from interactions between thermal expansion and mechanical properties, and both can be highly anisotropic. Thermal expansion anisotropy was found to be correlated with elastic anisotropy: axes with negative thermal expansion were less compliant.

A silica sol-gel design strategy for nanostructured metallic materials.

Batteries, fuel cells and solar cells, among many other high-current-density devices, could benefit from the precise meso- to macroscopic structure control afforded by the silica sol-gel process. The porous materials made by silica sol-gel chemistry are typically insulators, however, which has restricted their application. Here we present a simple, yet highly versatile silica sol-gel process built around a multifunctional sol-gel precursor that is derived from the following: amino acids, hydroxy acids or peptides; a silicon alkoxide; and a metal acetate.

A 43Ca and 13C NMR study of the chemical interaction between poly(ethylene-vinyl acetate) and white cement during hydration.

(43)Ca and (13)C NMR methods were used to study the chemical interaction of poly(ethylene-vinyl acetate) (PEVAc) admixture in commercial-grade white cement. From (43)Ca NMR it is shown both that PEVAc induces modest changes in the hydrated cement structure, and that hydrated commercial cement is significantly more complex than models that have been used for its structure in past work. The (13)C NMR results show that the PEVAc hydrolysis occurs early in the cement hydration acceleration period, with a rate well-fit by an exponential decay using a time constant of 6±1 days.

Design and applications of an in situ electrochemical NMR cell.

A device using a three-electrode electrochemical cell (referred to as an ECNMR cell) was successfully constructed that could be used in a standard 5mm NMR probe to acquire high-resolution NMR spectra while the working electrode was held at a constant electrical potential. The working electrode was a 20 nm thick gold film thermally coated on the outside of an inner 3mm glass tube. An underlayer consisting of (3-mercaptopropyl)trimethoxy-silane was coated on the glass surface in order to improve its adhesion to gold.

Computation of Mössbauer isomer shifts from first principles.

Computation of the observables of a Mössbauer spectrum, primarily the isomer shift, from a first-principles approach is described. The framework used is density functional theory using the projector augmented wave formalism (DFT PAW), which enables efficient computation even of many-electron solids such as SnCl(2). The proper PAW version of the isomer shift is derived and shown to be correct through comparison of computed shifts and experiment in a variety of compounds based on tin, germanium and zinc.

Observable effects of mechanical stress induced by sample spinning in solid state nuclear magnetic resonance.

The stress-induced change in chemical shielding induced by sample spinning is measured and interpreted theoretically. By considering the rotating sample as an elastic body in the plane-strain approximation, the internal stress field as a function of sample size, rotation frequency, and elastic constants is determined. This stress field and the dependence of chemical shielding on strain, as determined by first-principles calculations, are combined to predict the shielding dependence on rotation frequency under isothermal conditions in single crystal gallium phosphide.

Preferential binding of fluorine to aluminum in high peralkaline aluminosilicate glasses.

For two series of fluoride-containing aluminosilicate glasses of high peralkaline type, we apply 27Al, 19F, 29Si, and 23Na NMR spectroscopy to understand the structural changes introduced by the addition of alkali fluorides. Adding fluoride in concentrations above the solubility limit causes crystallization of different phases in sodium and potassium glasses despite identical composition. However, the NMR spectra reveal that the structural evolution of the precrystallized states is similar in both series.

A neutron scattering and nuclear magnetic resonance study of the structure of GeO2-P2O5 glasses.

Germanophosphate (GeO2-P2O5) glasses were studied with neutron diffraction, phosphorus, and oxygen nuclear magnetic resonance, calorimetry, viscosity measurements, and first-principles calculations. These data sets were combined to propose a structural model of GeO2-P2O5 glasses, which includes tetrahedrally coordinated phosphorus, formation of octahedrally coordinated germanium as P2O5 content increases, an absence of trigonally coordinated oxygen, and hence an absence of rutile-like GeO2 domains. The structural model was then used to propose explanations for both the observed composition dependence of the glass transition temperature and the fragility of the GeO2-P2O5 liquids.

On the spectral similarity of bridging and nonbridging oxygen in tellurites.

We show by high field (17)O solid-state nuclear magnetic resonance (NMR) and by ab initio calculations of both the NMR and the oxygen 1s photoelectron spectra that the oxygen sites in tellurite glasses show no spectroscopic distinction, even when comparing bridging and nonbridging sites. This is remarkable because two such sites differ formally by a full electronic charge, and they are readily distinguished by these same methods in silicates. We argue that this similarity arises from the symmetry breaking that occurs when the original TeO(2) crystal solid forms, due to the pseudo-Jahn-Teller distortion induced by the two additional valence electrons present in Te(IV) as compared to Si(IV).

Stress, strain, and NMR.

Experimental and ab initio results that demonstrate the effect of stress on the nuclear magnetic resonance spectra of materials are shown. The design of a cell that generates uniaxial compressive stress is presented, and results on gallium phosphide and lead nitrate single crystals that illustrate the observable results of the stress are shown. Tensors that relate stress and strain to changes in the chemical shielding tensors and the electric field gradient tensors are defined formally.

Functional polymer colloids with ordered interior.

Polymer colloids with internal ordering were synthesized using hydrolytic condensation of octadecyl-dimethyl(3-trimethoxysilylpropyl)ammonium chloride (ODMACl) and a mixture of ODMACl and the trisodium salt of the triacetic acid N-(trimethoxysilylpropyl)ethylenediamine (TANED). The structure and morphology of these colloids were studied with small-angle X-ray scattering, transmission electron microscopy, nuclear magnetic resonance, sedimentation in ultracentrifuge; and other methods. When polymer colloids are obtained from a single precursor (ODMACl), their local structure, molecular weight characteristics, and morphology strongly depend on the reaction conditions, while lamellar ordering remains nearly unaffected.

The NMR response of boroxol rings: a density functional theory study.

Cluster models of boron oxide glasses are studied computationally using density functional theory. It is shown that the isotropic chemical shielding of boron in boroxol rings is about 5 ppm less than for boron in non-ring BO3/2 units, and that the quadrupole coupling in ring sites is about 0.1 MHz larger than in non-ring sites, confirming assignments made in glasses and crystalline model compounds.

Structure and ionic interactions of organic-inorganic composite polymer electrolytes studied by solid-state NMR and Raman spectroscopy.

Solid-state NMR studies of composite polymer electrolytes are reported. The materials consist of polyethylene oxide and an organic inorganic composite, together with a lithium salt, and are candidates for electrolytes in solid-state lithium ion batteries. Silicon and aluminum MAS and multiple quantum MAS are used to characterize the network character of the organic-inorganic composite, and spin diffusion measurements are used to determine the nanostructure of the polymer/composite blending.

Platinum-containing hyper-cross-linked polystyrene as a modifier-free selective catalyst for L-sorbose oxidation.

Impregnation of hyper-cross-linked polystyrene (HPS) with tetrahydrofuran (THF) or methanol (ML) solutions containing platinic acid results in the formation of Pt(II) complexes within the nanocavities of HPS. Subsequent reduction of the complexes by H2 yields stable Pt nanoparticles with a mean diameter of 1.3 nm in THF and 1.

Through-bond connectivity in solids by continuous-wave spin lock.

A simple two-dimensional correlation experiment that enables determination of through-bond connectivity in the solid state is described. The experiment is performed under fast magic angle spinning (MAS) conditions. After the initial pi/2 pulse, the magnetization develops freely under the MAS Hamiltonian.

Modeling glasses using the reverse Monte Carlo algorithm: addition of nuclear magnetic resonance and expanded coordination number constraints.

In simple oxide glasses the coordination number and oxidation state of the glass-forming element can be predicted directly from the "8--n" rule. Tellurite glasses, however, are unusual in that the coordination number of oxygen around tellurium varies without a corresponding change in the oxidation state of tellurium. To model sodium tellurite glasses successfully using the reverse Monte Carlo algorithm several new constraints have been added.

Anisotropy-correlated spectroscopy of quadrupolar nuclei.

The two-dimensional anisotropy-correlated NMR (2DAC) spectra of half-integer quadrupolar nuclei may be recorded by using an exchange sequence in conjunction with magic angle spinning (MAS) during evolution and detection, and off-MAS during mixing. Application of this experiment to boron oxides is described, in addition to an analysis of the spin diffusion rates in such materials.