Local Environment Of Cations Research Articles

Morphological Studies of Lightly Sulfonated Polystyrene Using 23Na NMR. 2. Effects of Solution Casting

23 Na NMR is used to study the local environment of sodium cations in lightly sulfonated polystyrene ionomers (NaSPS). Solution casting is shown to have a significant effect on the local morphology of NaSPS. NaSPS with 1.7% styrenesulfonate groups cast from solutions of DMF or THF/water at low concentrations showed more aggregated ions than those samples cast from relatively nonpolar solvents such as THF and THF/methanol mixtures. No changes due to sample history were seen for more highly sulfonated sanaples (4.2% styrenesulfonate groups). The changes in morphology due to solution casting were shown to have some reversible character

X-Ray absorption studies of bi-based superconductors

X-Ray absorption (XANES and EXAFS) spectroscopic techniques have been applied to study the local structural environment of host and dopant cations in Bi-based high-Tc superconductors; the materials studied include the following: BaBiO3, BaBi1 –xPbxO3, Ba1 –xKxBiO3, Bi2Sr2CuO6, Bi2Sr2CaCu2O8 and Bi2Sr2Ca2Cu3O10. XANES spectroscopy has been used to determine the valence state of Bi, Pb and Cu in these materials. In BaBiO3 the valence state of Bi is found to be close to IV both in the pure and doped material, and a disproportionation of BiIV into BiIII and BiV is not indicated by analyses of these data. The valence state of Pb is also found to be IV in BaBi1 –xPbxO3. In Bi-based cuprate superconductors, the formal valence states of Bi and Cu are slightly higher than their stoichiometric values of III and II. EXAFS spectroscopy has been used to examine the local structure around Bi, Ba, Pb, Sr, Ca and Cu cations in these systems. In the BaBiO3 system, doping with Pb and K results in a decrease in the metal–oxygen bond lengths. The results indicate that the local environment of all cations in the Bi–Sr–Ca–Cu–O system is characterised by substantial static disorder.

X-ray absorption studies of La 2-x(Ba,Sr) xCuO 4 high-T c superconductors

Extended X-ray absorption fine structure (EXAFS) spectroscopy measurements have been used to study the local environment of different cations in high- T c superconducting compounds La 2- x (Ba,Sr) x CuO 4, with x = 0.15, 0.20. We show that the LaO bond length differs from the BaO and SrO bond lengths. The bond lengths between the dopant and oxygen atoms vary with the concentration of the dopant. The CuO bond lengths also vary on doping La 2CuO 4 with Ba or Sr at La sites. However, these variations are more significant for the CuO(2) bond (where O(2) is also bonded to a La (Ba,Sr) atom), than for the CuO(1) bond length.

Electronic and vibrational properties of hydroxylated and dehydroxylated thin Al 2O 2 films

The electronic and vibrational properties of planar thin-films (20–30 Å) of aluminum oxide on a Ru(001) substrate were studied using X-ray photoelectron (XPS), Auger, and high resolution electron energy loss (HREEL) spectroscopies. Hydroxylated Al 2O 3 films, prepared in water/oxygen mixtures or produced by exposure of dehydroxylated Al 2O 3 films to water vapor, exhibit OH stretching vibrations at ∼3730 cm −1, characteristic of isolated hydroxyl groups. It is particularly significant that the hydroxyl group stability on planar Al 2O 3 films, oxidized at pressures between several Torr and 1 atm, is shown to be comparable to that for alumina powders. This is taken as a strong indication that the planar oxide structure is similar to that of powder alumina surfaces. XPS and Auger spectra for the thin-film aluminas indicate Auger parameters and valence band densities-of-state comparable to those of powdered aluminas. The aluminum Auger parameter shifts from γ-like to α-like at least 200 K below transition temperatures for micron thick films, and 350 K below the bulk transition temperatures. Our 30 Å films are substantially thinner, and so the Auger parameter may be indicative of a low temperature phase transformation, but is certainly characteristic of a change in the local cation environment from a mixture of tetrahedral and octahedral cation occupation to only octahedral coordination. The surface phonon spectra of aluminas containing no excess Al 0 produce the characteristic three-peak vibrational spectrum. Calculations performed using the dielectric theory of electron energy loss spectroscopy confirm this characteristic phonon loss spectrum to be composed of both longitudinal (LO) and transverse (TO) surface optic modes.

Local environment of cations and ionomer morphology from nitrogen-14 superhyperfine interacting. ESR of copper dication in Nafion/acetonitrile

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTLocal environment of cations and ionomer morphology from nitrogen-14 superhyperfine interacting. ESR of copper dication in Nafion/acetonitrileJanusz Bednarek and Shulamith SchlickCite this: J. Am. Chem. Soc. 1990, 112, 13, 5019–5024Publication Date (Print):June 1, 1990Publication History Published online1 May 2002Published inissue 1 June 1990https://doi.org/10.1021/ja00169a004RIGHTS & PERMISSIONSArticle Views88Altmetric-Citations12LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (767 KB) Get e-Alerts Get e-Alerts

Multifrequency ESR and ENDOR studies of ionomers

AbstractWe describe methods for determining the local environment of cations and the process of ionic clustering in ionomers, using electron magnetic resonance spectroscopy. The distance between Cu2+ cations in perfluorinated membranes (Nafion) containing terminal sulfonic groups and swollen by water has been deduced from an analysis of ESR spectra at L (1.25 GHz), S (2.36 GHz) and X (9.36 GHz) bands, in membranes containing cupric ion concentrations in the range 1–30 percent of the total amount needed to fully neutralize the pendant acid groups. At higher cation concentrations ESR spectra indicate the presence of aggregated cations. The intercation distance determination is based on the simulation of spectra from isolated cations using distribution widths δg11 and δA11 and extraction of the residual width ΔHR, which is due to dipolar interactions. No aggregation is detected in membranes swollen by less polar solvents such as methanol, dimethylformamide (DMF) and tetrahydrofuran (THF); these results are in contrast to SAXS experiments in membranes swollen by methanol, which exhibit the “ionic peak”. Cu2+‐Cu2+ and Ti3+‐Ti3+ dimers have been detected in Nafion swollen by water, methanol, DMF and THF, and have been characterized by an analysis of the spin‐forbidden half‐field Δms=2 transition, and by computer simulations. The intercation distance in the cupric dimers, deduced from the intensity ratio of the Δms=2 and Δms=1 dimer transitions, is 5.0±0.2 Å. A model for the dimer has been proposed, which explains the crosslinking of the polymer chains by the metal cations. ENDOR signals from 1H, 2H and 19F nuclei have been detected in Nafion neutralized by Ti3+. The ENDOR results allow determination of the local environment of the paramagnetic cations, to a distance of ∼10 Å.

Synchrotron‐based X ray absorption studies of cation environments in Earth materials

Since its development in the early 1970s, synchrotron‐based X ray absorption spectroscopy (XAS) has proven to be a versatile structural probe for studying the local environments of cations in a variety of earth materials ranging from crystalline solids, silicate glasses, and high‐temperature silicate melts to aqueous sorption systems which involve metal complexes associated with (or sorbed at) mineral/water interfaces. The structural information provided by XAS includes average interatomic distances and the number and chemical identities of neighbors within 5–6 Å of a selected cation. In many cases (e.g., short‐range ordering of cations in minerals; cation environments in gels, glasses, melts, and metamict (radiation damaged) minerals; and the structure and composition of sorbed species at mineral/water interfaces), XAS provides unique structural data not duplicated by other methods. This paper presents a tutorial review of the physics underlying XAS and data analysis methods and a selective review of applications of XAS to earth materials.

Local environment and clustering of cations in ionomers. ESR of copper(II) in Nafion swollen by water, methanol, dimethylformamide, and tetrahydrofuran

Local environment and clustering of cations in ionomers. ESR of copper(II) in Nafion swollen by water, methanol, dimethylformamide, and tetrahydrofuran

The local environment of metal sites in intracellular granules investigated by using X-ray-absorption spectroscopy.

We report the use of X-ray-absorption spectroscopy (x.a.s.) to study the local atomic environment of cations in intracellular granules from the hepatopancreas of Helix aspersa. Both the calcium K-edge in these concretions and the manganese K-edge in doped specimens were measured. Electron-microprobe measurements confirm that the introduced Mn2+ is concentrated in irregular growths on the surfaces of the granules. The near-edge structure (x.a.n.e.s.) of calcium is similar to that of manganese, indicating that the oxygen-co-ordination spheres of both cations share a similar symmetry. From the extended structure (e.x.a.f.s.) the metal-oxygen bond lengths of 0.230 nm (2.30A) for Ca-O and 0.218 nm (2.18A) for Mn-O [+/- 0.004 nm (0.04A)] were determined, reference being made to a variety of model compounds. The low density of the granules (2.07 g/cm3), together with the local atomic distribution, suggest an open hydrated structure for these phosphate deposits. Detailed analysis of the distribution of nearest-neighbour oxygen atoms demonstrates that this is asymmetric and considerably broader for Ca2+ than for Mn2+. Compared with the model compounds, the Ca2+ environment in the granules is similar to that observed in Ca2P2O7. I.r. spectra indicate the presence of condensed phosphate groups in the granules, with the strong possibility these are pyrophosphate (P2O7(4-) groups.