17O MAS NMR - Explore the Science & Experts | ideXlab

Scan Science and Technology

Contact Leading Edge Experts & Companies

17O MAS NMR

The Experts below are selected from a list of 11733 Experts worldwide ranked by ideXlab platform

17O MAS NMR – Free Register to Access Experts & Abstracts

Clare P. Grey – One of the best experts on this subject based on the ideXlab platform.

  • Probing Oxide-Ion Mobility in the Mixed Ionic–Electronic Conductor La2NiO4+δ by Solid-State 17O MAS NMR Spectroscopy
    Journal of the American Chemical Society, 2016
    Co-Authors: David M. Halat, Riza Dervisoglu, Gunwoo Kim, Matthew T. Dunstan, Frédéric Blanc, Derek S. Middlemiss, Clare P. Grey

    Abstract:

    While solid-state NMR spectroscopic techniques have helped clarify the local structure and dynamics of ionic conductors, similar studies of mixed ionic-electronic conductors (MIECs) have been hampered by the paramagnetic behavior of these systems. Here we report high-resolution (17)O (I = 5/2) solid-state NMR spectra of the mixed-conducting solid oxide fuel cell (SOFC) cathode material La2NiO4+δ, a paramagnetic transition-metal oxide. Three distinct oxygen environments (equatorial, axial, and interstitial) can be assigned on the basis of hyperfine (Fermi contact) shifts and quadrupolar nutation behavior, aided by results from periodic DFT calculations. Distinct structural distortions among the axial sites, arising from the nonstoichiometric incorporation of interstitial oxygen, can be resolved by advanced magic angle turning and phase-adjusted sideband separation (MATPASS) NMR experiments. Finally, variable-temperature spectra reveal the onset of rapid interstitial oxide motion and exchange with axial sites at ∼130 °C, associated with the reported orthorhombic-to-tetragonal phase transition of La2NiO4+δ. From the variable-temperature spectra, we develop a model of oxide-ion dynamics on the spectral time scale that accounts for motional differences of all distinct oxygen sites. Though we treat La2NiO4+δ as a model system for a combined paramagnetic (17)O NMR and DFT methodology, the approach presented herein should prove applicable to MIECs and other functionally important paramagnetic oxides.

  • probing oxide ion mobility in the mixed ionic electronic conductor la2nio4 δ by solid state 17O MAS NMR spectroscopy
    Journal of the American Chemical Society, 2016
    Co-Authors: David M. Halat, Riza Dervisoglu, Gunwoo Kim, Matthew T. Dunstan, Frédéric Blanc, Derek S. Middlemiss, Clare P. Grey

    Abstract:

    While solid-state NMR spectroscopic techniques have helped clarify the local structure and dynamics of ionic conductors, similar studies of mixed ionic-electronic conductors (MIECs) have been hampered by the paramagnetic behavior of these systems. Here we report high-resolution (17)O (I = 5/2) solid-state NMR spectra of the mixed-conducting solid oxide fuel cell (SOFC) cathode material La2NiO4+δ, a paramagnetic transition-metal oxide. Three distinct oxygen environments (equatorial, axial, and interstitial) can be assigned on the basis of hyperfine (Fermi contact) shifts and quadrupolar nutation behavior, aided by results from periodic DFT calculations. Distinct structural distortions among the axial sites, arising from the nonstoichiometric incorporation of interstitial oxygen, can be resolved by advanced magic angle turning and phase-adjusted sideband separation (MATPASS) NMR experiments. Finally, variable-temperature spectra reveal the onset of rapid interstitial oxide motion and exchange with axial sites at ∼130 °C, associated with the reported orthorhombic-to-tetragonal phase transition of La2NiO4+δ. From the variable-temperature spectra, we develop a model of oxide-ion dynamics on the spectral time scale that accounts for motional differences of all distinct oxygen sites. Though we treat La2NiO4+δ as a model system for a combined paramagnetic (17)O NMR and DFT methodology, the approach presented herein should prove applicable to MIECs and other functionally important paramagnetic oxides.

  • Probing brønsted acid sites in zeolite HY with low temperature 17O MAS NMR spectroscopy
    From Zeolites to Porous MOF Materials – The 40th Anniversary of International Zeolite Conference Proceedings of the 15th International Zeolite Confere, 2007
    Co-Authors: Hua Huo, Luming Peng, Clare P. Grey

    Abstract:

    Abstract Bronsted acid sites play a key role in controlling the catalytic performances of acidic catalysts. A determination of the structure of the acid site is fundamental to the understanding acid strength in these systems. The O-H distances in zeolite HY and HZSM-5 extracted from 17O-1H REDOR NMR data acquired at room temperature are noticeably longer than the results from calculations due to the presence of some restricted motions at room temperature, such as zeolite framework vibrations and O-H librational motion. We present here our 17O-1H REDOR NMR results of zeolite HY at a lower temperature of 183 K, where some of these motions are frozen out. By comparing the line shapes obtained from simulations performed with the SIMPSON package with the experimental data, an O-H distance of about 0.97 ∼ 0.98 A was obtained, which is consistent with the previous ab-initio calculation results. The results indicate that low temperature REDOR NMR spectroscopy can provide estimates of the O-H distance, which should prove useful in understanding zeolite structure and acidity.

Namjun Kim – One of the best experts on this subject based on the ideXlab platform.

  • Structure of Amorphous Tantalum Oxide and Titania-Doped Tantala: 17O NMR Results for Sol–Gel and Ion-Beam-Sputtered Materials
    Chemistry of Materials, 2011
    Co-Authors: Namjun Kim, Jonathan F Stebbins

    Abstract:

    Amorphous thin films of high-refractive index metal oxides such as Ta2O5 are critical in multilayer optical components such as the main mirrors of the Laser Interferometer Gravitational-Wave Observatory (LIGO), but their atomic-scale structures are not well-known. Amorphous, pure, and titania-doped tantalum oxides were prepared by sol–gel synthesis and by ion-beam sputtering. The samples were successfully enriched with the nuclear magnetic resonance (NMR)-active 17O isotope by heating them in 17O2 gas, and they were studied using 17O solid-state NMR. 17O MAS NMR spectra of pure tantala show two resonances that correspond to two- and three-coordinated oxygens, allowing the average oxygen coordination numbers to be estimated from the relative peak areas. The average coordination number for oxide ions seems to increase as tantala changes from amorphous to crystalline. Titania-doped tantalas, (Ta1–xTix)2O5–x with x = 0.10, 0.25, and 0.50, were also studied. At the lower two dopant levels, Ta and Ti cations ar…

  • High temperature 17O MAS NMR study of calcia, magnesia, scandia and yttria stabilized zirconia
    Solid State Ionics, 2007
    Co-Authors: Namjun Kim, Cheng-han Hsieh, Hong Huang, Fritz B. Prinz, Jonathan F Stebbins

    Abstract:

    Abstract High-resolution 17 O MAS NMR can provide unique constraints on local structure and oxide ion dynamics in conductive zirconia ceramics of interest for fuel cells and other technologies. We describe here NMR and bulk conductivity measurements for scandia, yttria, calcia, and magnesia stabilized zirconias, including MAS NMR spectra collected in situ at temperatures up to 700 °C. All of the cubic compounds with high dopant levels showed line narrowing and coalescence in this temperature range, and the temperature-induced changes in line widths are qualitatively correlated with the bulk conductivities. A monoclinic zirconia with 2% Sc 2 O 3 dopant level (expected to have relatively low ionic mobility) showed no motional averaging of its two 17 O NMR peaks even at 600 °C, but instead is observed to begin to transform to a disordered, possibly cubic or tetragonal phase at 600 to 700 °C. 17 O MAS NMR spectra of calcia stabilized zirconia were analyzed in detail and the exchange frequencies as a function of temperature, conductivity, and activation energy were estimated and compared with bulk conductivities. The activation energy estimated from NMR exchange frequencies is somewhat lower than that of bulk conductivity but the conductivities estimated from NMR appear to be lower than bulk conductivity.

  • Vacancy and Cation Distribution in Yttria-Doped Ceria: An 89Y and 17O MAS NMR Study
    Chemistry of Materials, 2007
    Co-Authors: Namjun Kim, Jonathan F Stebbins

    Abstract:

    The local structure and dynamics of oxide ions in yttria-doped ceria (YDC, 5 to 30% Y2O3) were studied using high-resolution 89Y and 17O MAS NMR spectroscopy at ambient temperature and high temperatures to 500 °C. Eight-, seven-, and six-coordinated yttrium cations are clearly resolved in 89Y MAS NMR spectra, and their relative populations were measured. The derived average coordination number of yttrium is smaller than that for a random distribution of oxygen vacancies, suggesting that there is strong association between yttrium cations and vacancies and there is the possibility of pairing of two yttrium cations with one vacancy. In the 17O MAS NMR spectra, resonances for oxygens with different coordination environments are resolved and are assigned to oxygens with different numbers of yttrium cations in the first coordination sphere. The relative intensities of the 17O resonances also deviate from those expected from a random distribution, again indicating possible pairing of yttrium cations. High-tempe…

Mark Smith – One of the best experts on this subject based on the ideXlab platform.

  • A multinuclear solid state NMR, density functional theory and X-Ray diffraction study of hydrogen bonding in Group I hydrogen dibenzoates
    CrystEngComm, 2013
    Co-Authors: Gregory J. Rees, Andrew P. Howes, Dinu Iuga, Stephen Day, Alberth Lari, Mateusz B. Pitak, Simon J. Coles, Terry L. Threlfall, Mark E. Light, Mark Smith

    Abstract:

    An NMR crystallographic approach incorporating multinuclear solid state NMR (SSNMR), X-ray structure determinations and density functional theory (DFT) are used to characterise the H bonding arrangements in benzoic acid (BZA) and the corresponding Group I alkali metal hydrogen dibenzoates (HD) systems. Since the XRD data often cannot precisely confirm the proton position within the hydrogen bond, the relationship between the experimental SSNMR parameters and the ability of gauge included plane augmented wave (GIPAW) DFT to predict them becomes a powerful constraint that can assist with further structure refinement. Both the 1H and 13C MAS NMR methods provide primary descriptions of the H bonding via accurate measurements of the 1H and 13C isotropic chemical shifts, and the individual 13C chemical shift tensor elements; these are unequivocally corroborated by DFT calculations, which together accurately describe the trend of the H bonding strength as the size of the monovalent cation changes. In addition, 17O MAS and DOR NMR form a powerful combination to characterise the O environments, with the DOR technique providing highly resolved 17O NMR data which helps verify unequivocally the number of inequivalent O positions for the conventional 17O MAS NMR to process. Further multinuclear MAS and static NMR studies involving the quadrupolar 7Li, 39K, 87Rb and 133Cs nuclei, and the associated DFT calculations, provide trends and a corroboration of the H bond geometry which assist in the understanding of these arrangements. Even though the crystallographic H positions in each H bonding arrangement reported from the single crystal X-ray studies are prone to uncertainty, the good corroboration between the measured and DFT calculated chemical shift and quadrupole tensor parameters for the Group I alkali species suggest that these reported H positions are reliable.

  • 17O and 15N solid state NMR studies on ligand-assisted templating and oxygen coordination in the walls of mesoporous Nb, Ta and Ti oxides.
    Journal of the American Chemical Society, 2008
    Co-Authors: Yuxiang Rao, Mark Smith, Thomas F. Kemp, Michel Trudeau, Dave M. Antonelli

    Abstract:

    A multinuclear solid state NMR approach is applied to four templated mesoporous oxides (silica, titania, niobia and tantala) to include 15N and 17O magic angle spinning (MAS) NMR and double resonance 15N−93Nb, 17O Rotational-Echo Adiabatic Passage Double Resonance (REAPDOR). The templated samples were ramped in steps of 20 °C for 2 days up to typically 110 °C where the samples were left for 2−4 days. 15N MAS NMR shows that amines are the only species present in the TiO2, Nb2O5, and Ta2O5. In SiO2, amines are only present as a minor coordination (10 ± 2%), but there are several strong ammonium 15N resonances. The REAPDOR experiments show that the nitrogen interacts with niobium, confirming a ligand interaction between the Nb and N, as previously believed. In the case of silica, the amine is quaternized and there is apparently no interaction with the Si, suggesting a RNH3+ −O−Si- hydrogen-bonding interaction with the walls. 17O MAS NMR provides the clearest indication of the local wall structure. In the aged, templated samples in all cases only OM2 coordinations are present which is very different from the pure bulk oxides (apart from SiO2) and must be due to the effects of amine coordination at the metal centers. On removal of the template, these oxides behave differently, with Ta2O5 showing a mixture of OTa2 (85 ± 5%) and OTa3 (15 ± 5%) which is similar to the types of coordination found in the bulk oxide. The previously reported 17O MAS NMR data from heat-treated mesoporous niobia shows only ONb2, which is very highly ordered. In contrast for titania, the OTi2 coordination is immediately lost on removal of the template to be replaced by a mixture of OTi3 (60 ± 5%) and OTi4 (40 ± 5%), with the OTi4 becoming dominant above 250 °C, very different behavior from the corresponding bulk oxide. In summary, this NMR study shows that the local oxygen coordination in amine-templated mesoporous transition metal oxides is present as OM2 which is relatively rare in bulk oxides. The data indicates that the template interaction is largely controlled by the N−M dative bond to the wall, suppressing higher oxygen coordination numbers. Qualitatively it appears that the strength of this interaction varies greatly in the different mesoporous oxides.

  • Experimental and Theoretical 17O NMR Study of the Influence of Hydrogen-Bonding on CO and O−H Oxygens in Carboxylic Solids
    The journal of physical chemistry. A, 2006
    Co-Authors: Alan Wong, Kevin J. Pike, Robert D. Jenkins, Guy J. Clarkson, Tiit Anupõld, Andrew P. Howes, David H. G. Crout, Ago Samoson, Ray Dupree, Mark Smith

    Abstract:

    A systematic solid-state 17O NMR study of a series of carboxylic compounds, maleic acid, chloromaleic acid, KH maleate, KH chloromaleate, K2 chloromaleate, and LiH phthalate·MeOH, is reported. Magic-angle spinning (MAS), triple-quantum (3Q) MAS, and double angle rotation (DOR) 17O NMR spectra were recorded at high magnetic fields (14.1 and 18.8 T). 17O MAS NMR for metal-free carboxylic acids and metal-containing carboxylic salts show featured spectra and demonstrate that this combined, where necessary, with DOR and 3QMAS, can yield site-specific information for samples containing multiple oxygen sites. In addition to 17O NMR spectroscopy, extensive quantum mechanical calculations were carried out to explore the influence of hydrogen bonding at these oxygen sites. B3LYP/6-311G++(d,p) calculations of 17O NMR parameters yielded good agreement with the experimental values. Linear correlations are observed between the calculated 17O NMR parameters and the hydrogen bond strengths, suggesting the possibility of …