The Experts below are selected from a list of 5706 Experts worldwide ranked by ideXlab platform
Lianpin Hwang - One of the best experts on this subject based on the ideXlab platform.
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the influence of adsorbed molecules on na sites in nay zeolite investigated by triple quantum 23Na MAS NMR spectroscopy
Solid State Nuclear Magnetic Resonance, 1998Co-Authors: Lianpin HwangAbstract:Abstract The effect of hydration and benzene adsorption on 23 Na resonance and the quadrupolar interaction in NaY zeolites is studied by triple-quantum MAS 23 Na NMR spectroscopy. In the case of a C6D6/NaY system, the results show that with an increase in benzene loading, there is an up-field trend in isotropic chemical shift (δCS) and a decreasing second order quadrupolar effect (χs) for the site II sodium ions. It was found that adsorbed benzene molecules have a slight effect on the environment of sodium ions on site I. All the sodium sites in NaY are influenced upon hydration. The up-field shift of the sodium δCS reflects the effect of coordination of oxygen atoms on sodium cations due to hydration. The magnitude of χs for hydrated sodium sites increases and then falls off with water loading. The increase in χs is due to the initial hydration among SI-, SI′- and SII-sodium ions, while the decrease is the result of approaching the final stage of saturated hydration.
Kenneth D M Harris - One of the best experts on this subject based on the ideXlab platform.
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triple quantum 23Na MAS NMR spectroscopy as a technique for probing polymorphism in sodium salts
Crystal Growth & Design, 2008Co-Authors: Kenneth D M HarrisAbstract:Triple-quantum 23Na MAS NMR spectroscopy has been applied to characterize the three polymorphs of sodium acetate. The crystallographically distinct sodium sites in each of these polymorphs are uniquely identified from the triple-quantum 23Na MAS NMR spectra. These data provide access to the 23Na quadrupole interaction parameters (quadrupole coupling constant and asymmetry parameter) for each sodium site, which provide a quantitative measure of the local structural properties of the sodium cations in each polymorphic form.
B Boddenberg - One of the best experts on this subject based on the ideXlab platform.
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erratum to 23Na solid state MAS NMR of sodium halides occluded in zeolites
Solid State Nuclear Magnetic Resonance, 1998Co-Authors: A Seidel, B Schimiczek, U Tracht, B BoddenbergAbstract:Occlusion of sodium chloride and sodium bromide in zeolitic pores was performed by heating mixtures of the salts with zeolites NaY and NaA under high vacuum conditions. The obtained samples were subjected to various further pretreatments like washing with water and zinc-exchange, and were investigated spectroscopically with the 23Na MAS NMR technique at various Zeeman field strengths. In the case of NaY, the halides are occluded in both types of cages of the faujasite structure. About 90% of the sodalite cages are shown to have incorporated salt which is concluded to be part of [Na4Hal]3+ clusters as in the case of sodalite type materials.
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23Na solid state MAS NMR of sodium halides occluded in zeolites
Solid State Nuclear Magnetic Resonance, 1997Co-Authors: A Seidel, B Schimiczek, U Tracht, B BoddenbergAbstract:Occlusion of sodium chloride and sodium bromide in zeolitic pores was performed by heating mixtures of the salts with zeolites NaY and NaA under high vacuum conditions. The obtained samples were subjected to various further pretreatments like washing with water and zinc-exchange, and were investigated spectroscopically with the 23Na MAS NMR technique at various Zeeman field strengths. In the case of NaY, the halides are occluded in both types of cages of the faujasite structure. About 90% of the sodalite cages are shown to have incorporated salt which is concluded to be part of [Na4Hal]3+ clusters as in the case of sodalite type materials.
Jonathan F Stebbins - One of the best experts on this subject based on the ideXlab platform.
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anionic speciation in sodium and potassium silicate glasses near the metasilicate na k 2sio3 composition 29si 17o and 23Na MAS NMR
Journal of Non-Crystalline Solids: X, 2020Co-Authors: Jonathan F StebbinsAbstract:Abstract Alkali silicate glasses near to the metasilicate composition provide sensitive tests of anionic speciation. However, reports on 29Si NMR data vary considerably in their derived proportions of silicate species. In some cases, an apparent deficit in the content of non-bridging oxygen has been attributed to up to 5 to 10% “free” oxide ions. Here we provide new NMR data on a series of sodium silicate glasses ranging from 56 to 45 mol% silica with accurately analyzed compositions. High signal-to-noise data for a 29Si-enriched glass provide improved constraints on fitting models for spectra, and suggests a slight asymmetry in the main Q2 component. Data are consistent with conventional models in which “free” oxide contents are below detection limits of about 0.5 to 1%. Spectra for an 17O-enriched K-silicate glass with about 53% silica confirm that there is no obvious direct signature for “free” oxide species in this compositional range.
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temperature calibration for high temperature MAS NMR to 913 k 63cu MAS NMR of cubr and cui and 23Na MAS NMR of nanbo3
Solid State Nuclear Magnetic Resonance, 2011Co-Authors: N Kim, Jonathan F StebbinsAbstract:The solid-state phase transitions of CuBr, CuI and NaNbO(3) can be readily observed using (63)Cu and (23)Na high-temperature magic-angle spinning nuclear magnetic resonance spectroscopy. Temperature has large, linear effects on the peak maximum of (63)Cu in each solid phase of CuBr and CuI, and there is large jump in shift across each phase transition. The (23)Na MAS NMR peak intensities and the line widths in NaNbO(3) also clearly show its high-temperature transition to the cubic phase. These data can be used to calibrate high-temperature MAS NMR probes up to 913 K, which is two hundred degrees higher than the commonly-used temperature calibration based on the chemical shift of (207)Pb in Pb(NO(3))(2).
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effects of cation field strength on the structure of aluminoborosilicate glasses high resolution 11b 27al and 23Na MAS NMR
Journal of Non-crystalline Solids, 2009Co-Authors: Jingshi Wu, Jonathan F StebbinsAbstract:Among the most important adjustable compositional variables in controlling glass and glass-melt properties are the relative proportions of network modifiers with varying cation field strength (ratio of charge to radius). Here we determine the details of structural changes caused by variations in the ratio CaO/Na2O in two series of aluminoborosilicate glasses with different contents of boron oxide. Using high-resolution, high field 11B and 27Al MAS NMR, we report precise values of contents of three- and four-coordinated boron (N4) and of four- and five-coordinated aluminum ([5]Al), and calculate fractions of non-bridging oxygens (NBOs). Increasing CaO/Na2O dramatically lowers N4 and increases NBO and [5]Al, but effects are non-linear with composition. Boron content affects these trends because of energetic constraints of mixing of various network cations. 23Na spectra reveal slight but systematic increases in the mean Na–O distance with increasing CaO/Na2O, suggesting that in Ca-rich glasses, Na+ has a higher ratio of bridging to non-bridging oxygens in its coordination shell. All of these changes can be understood by the tendency of higher field strength modifier cations to promote the concentration of negative charges on non-bridging oxygens in their local coordination environment, systematically converting four- to three-coordinated boron.
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high temperature 23Na MAS NMR data for albite comparison to chemical shift models
American Mineralogist, 1995Co-Authors: A M George, Jonathan F StebbinsAbstract:Recently, correlations of 23Na chemical shifts with structural parameters such as bond length, coordination number, and bond strength in inorganic compounds have been proposed. When considering only silicate materials we have found that some of these models lead to conflicting predictions. To test the applicability of these correlations to silicates, we collected 23Na MAS NMR spectra of a pure, ordered albite (NaAISi30g) from 25 to 352°C. Over this temperature range, the Na-O bond lengths increase, and the measured isotropic shifts relative to 1 M NaCI decrease linearly from -7.1 ppm at room temperature to -7.8 ppm at 352°C. This agrees with the observed trend in silicates of increasing bond length leading to more negative values of 0 but is not consistent with the bond-valence model, which predicts a change of several parts per million in the opposite direction over this temperature range. Quadrupolar coupling constants were also seen to change, decreasing linearly with temperature from 2.69 MHz at 20°C to 2.30 MHz at 352°C. Static spectra measured from 22 to 1020 °C yielded values consistent with this in the low-temperature range and continued to decrease linearly to 1.50 MHz at the highest temperature. The 23Na spin-lattice relaxation times (T1) were collected between 25 and 1140 °C as well. T[ decreases gradually up to about 500°C and then drops rapidly, indicating that there is a change in the relaxation mechanism at this temperature.
Dany Carlier - One of the best experts on this subject based on the ideXlab platform.
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original layered op4 li na xcoo2 phase insights on its structure electronic structure and dynamics from solid state NMR
Inorganic Chemistry, 2020Co-Authors: Yohan Biecher, Gillian R. Goward, Danielle L Smiley, Marie Guignard, Francois Fauth, Romain Berthelot, Claude Delmas, Dany CarlierAbstract:The OP4-(Li/Na)xCoO2 phase is an unusual lamellar oxide with a 1:1 alternation between Li and Na interslab spaces. In order to probe the local structure, electronic structure, and dynamics, 7Li and 23Na magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy was performed in complementarity to X-ray diffraction and electronic and magnetic properties measurements. 7Li MAS NMR showed that NMR shifts result from two contributions: the Fermi contact and the Knight shifts due to the presence of both localized and delocalized electrons, which is really unusual. 7Li MAS NMR clearly shows several Li environments, indicating that, moreover, Co ions with different local electronic structures are formed, probably due to the arrangement of the Na+ ions in the next cationic layer. 23Na MAS NMR showed that some Na+ ions are located in the Li layer, which was not previously considered in the structural model. The Rietveld refinement of the synchrotron XRD led to the OP4-[Li0.42Na0.05]Na0.32CoO2 formula for the material. In addition, 7Li and 23Na MAS NMR spectroscopies provide information about the cationic mobility in the material: Whereas no exchange is observed for 7Li up to 450 K, the 23Na spectrum already reveals a single average signal at room temperature due to a much larger ionic mobility.
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a layered iron iii phosphate phase na3fe3 po4 4 synthesis structure and electrochemical properties as positive electrode in sodium batteries
Journal of Physical Chemistry C, 2010Co-Authors: Khiem Trad, Dany Carlier, Laurence Croguennec, Alain Wattiaux, Besma Lajmi, Mongi Ben Amara, C DelmasAbstract:For the first time, a powder of Na3Fe3(PO4)4 was obtained by solid state reaction. It crystallizes in monoclinic space group C2/c in good agreement with previous studies of a single crystal. The Rietveld refinement of the XRD pattern showed line broadening of some diffraction lines associated with size and strain effects. Its layered structure can be described by complex layers of corner-sharing FeO6 octahedra connected by PO4 tetrahedra through corner and edge sharing. The Na+ ions are located in the interslab space. The local environments of Fe, Na, and P were characterized by 57Fe Mossbauer spectroscopy and 23Na and 31P MAS NMR. A Second ORder Graphic Extrapolation (SORGE) diagram as introduced by MASsiot et al. allowed us to fully interpret the 23Na MAS NMR spectrum that exhibits three signals for two crystallographic Na sites. The electrochemical properties of Na3Fe3(PO4)4 were tested in sodium cells. Ex situ and in situ X-ray diffraction data and Mossbauer spectroscopy measurements indicate that the...
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sodium ion mobility in naxcoo2 0 6 x 0 75 cobaltites studied by 23Na MAS NMR
Inorganic Chemistry, 2009Co-Authors: Dany Carlier, Maxime Blangero, Michel Menetrier, Michael Pollet, J P Doumerc, C DelmasAbstract:Various P2 and P'3-Na(x)CoO(2) phases, with x ranging approximately from 0.6 to 0.75, have been studied by variable-temperature (23)Na magic angle spinning (MAS) NMR. Signal modification versus temperature plots clearly show that Na(+) ions are not totally mobile at room temperature on the NMR time scale. As the temperature increases, the line shape change of the (23)Na MAS NMR signal differs for the P2 and P'3 stackings and is interpreted by the differences of Na(+) ion sites and of sodium diffusion pathways in the two structures.
