Structural modulation in the high capacity battery cathode material LiFeBO3

The crystal structure of the promising Li-ion battery cathode material LiFeBO(3) has been redetermined based on the results of single crystal X-ray diffraction data. A commensurate modulation that doubles the periodicity of the lattice in the a-axis direction is observed. When the structure of LiFeBO(3) is refined in the 4-dimensional superspace group C2/c(α0γ)00, with α = 1/2 and γ = 0 and with lattice parameters of a = 5.1681 ?, b = 8.8687 ?, c = 10.1656 ?, and β = 91.514°, all of the disorder present in the prior C2/c structural model is eliminated and a long-range ordering of 1D chains of corner-shared LiO(4) is revealed to occur as a result of cooperative displacements of Li and O atoms in the c-axis direction. Solid-state hybrid density functional theory calculations find that the modulation stabilizes the LiFeBO(3) structure by 1.2 kJ/mol (12 meV/f.u.), and that the modulation disappears after delithiation to form a structurally related FeBO(3) phase. The band gaps of LiFeBO(3) and FeBO(3) are calculated to be 3.5 and 3.3 eV, respectively. Bond valence sum maps have been used to identify and characterize the important Li conduction pathways, and suggest that the activation energies for Li diffusion will be higher in the modulated structure of LiFeBO(3) than in its unmodulated analogue.     

Electronic spin transition in nanosize stoichiometric lithium cobalt oxide

A change in the electronic spin state of the surfaces relevant to Li (de)intercalation of nanosized stoichiometric lithium cobalt oxide LiCo(III)O(2) from low-spin to intermediate and high spin is observed for the first time. These surfaces are the ones that are relevant for Li (de)intercalation. From density functional theory calculations with a Hubbard U correction, the surface energies of the layered lithium cobalt oxide can be significantly lowered as a consequence of the spin change. The crystal field splitting of Co d orbitals is modified at the surface due to missing Co-O bonds. The electronic spin transition also has a significant impact on Co(III)-Co(IV) redox potential, as revealed by the change in the lithium (de)intercalation voltage profile in a lithium half cell.     

Probing Cation and Vacancy Ordering in the Dry and Hydrated Yttrium-Substituted BaSnO(3) Perovskite by NMR Spectroscopy and First Principles Calculations: Implications for Proton Mobility

Hydrated BaSn(1-x)Y(x)O(3-x/2) is a protonic conductor that, unlike many other related perovskites, shows high conductivity even at high substitution levels. A joint multinuclear NMR spectroscopy and density functional theory (total energy and GIPAW NMR calculations) investigation of BaSn(1-x)Y(x)O(3-x/2) (0.10 ≤ x ≤ 0.50) was performed to investigate cation ordering and the location of the oxygen vacancies in the dry material. The DFT energetics show that Y doping on the Sn site is favored over doping on the Ba site. The (119)Sn chemical shifts are sensitive to the number of neighboring Sn and Y cations, an experimental observation that is supported by the GIPAW calculations and that allows clustering to be monitored: Y substitution on the Sn sublattice is close to random up to x = 0.20, while at higher substitution levels, Y-O-Y linkages are avoided, leading, at x = 0.50, to strict Y-O-Sn alternation of B-site cations. These results are confirmed by the absence of a "Y-O-Y" (17)O resonance and supported by the (17)O NMR shift calculations. Although resonances due to six-coordinate Y cations were observed by (89)Y NMR, the agreement between the experimental and calculated shifts was poor. Five-coordinate Sn and Y sites (i.e., sites next to the vacancy) were observed by (119)Sn and (89)Y NMR, respectively, these sites disappearing on hydration. More five-coordinated Sn than five-coordinated Y sites are seen, even at x = 0.50, which is ascribed to the presence of residual Sn-O-Sn defects in the cation-ordered material and their ability to accommodate O vacancies. High-temperature (119)Sn NMR reveals that the O ions are mobile above 400 °C, oxygen mobility being required to hydrate these materials. The high protonic mobility, even in the high Y-content materials, is ascribed to the Y-O-Sn cation ordering, which prevents proton trapping on the more basic Y-O-Y sites.     

Isotropic high field NMR spectra of Li-ion battery materials with anisotropy >1 MHz

The use of a magic-angle turning and phase-adjusted spinning sideband NMR experiment to resolve and quantify the individual local environments in the high field (7)Li and (31)P NMR spectra of paramagnetic lithium-ion battery materials is demonstrated. The use of short radio frequency pulses provides an excitation bandwidth that is sufficient to cover shift anisotropy of >1 MHz in breadth, allowing isotropic and anisotropic components to be resolved.     

Matrix‐assisted laser desorption/ionization tissue profiling of secretoneurin in the nucleus accumbens shell from cocaine‐sensitized rats

Proteins in the nucleus accumbens mediate many cocaine‐induced behaviors. In an effort to measure changes in nucleus accumbens protein expression as potential biomarkers for addiction, coronal tissue sections were obtained from rats that developed behavioral sensitization after daily administration of cocaine, or from daily saline‐treated controls. The tissue sections were subjected to matrix‐assisted laser desorption/ionization (MALDI) mass spectrometry (MS) profiling and tissue imaging. For profiling experiments, brain sections were manually spotted with matrix over the nucleus accumbens, a brain region known to regulate cocaine sensitization. Summed mass spectra (10 000 laser shots, grid) were acquired and spectra were aligned to reference peaks. Using bioinformatics tools, eight spectral features were found to be altered by cocaine treatment. Based on additional sequencing experiments with MALDI tandem MS and database searches of measured masses, secretoneurin (m/z 3653) was identified as having an increased expression. In addition, the distribution of m/z 3653 in the nucleus accumbens was determined by MALDI tissue imaging, and the increased expression of its precursor protein, secretogranin II, was verified by immunoblotting. Copyright © 2009 John Wiley & Sons, Ltd.     

Real-time NMR studies of electrochemical double-layer capacitors

(11)B NMR spectroscopy has been used to investigate the sorption of BF(4)(-) anions on a highly porous, high surface area carbon, and different binding sites have been identified. By implementing in situ NMR approaches, the migration of ions between the electrodes of the supercapacitors and changes in the nature of ion binding to the surface have been observed in real time.     

Defects in doped LaGaO3 anionic conductors: linking NMR spectral features, local environments, and defect thermodynamics

Doped lanthanum gallate perovskites (LaGaO(3)) constitute some of the most promising electrolyte materials for solid oxide fuel cells operating in the intermediate temperature regime. Here, an approach combining experimental multinuclear NMR spectroscopy with density functional theory total energy and GIPAW NMR calculations yields a comprehensive understanding of the structural and defect chemistries of Sr- and Mg-doped LaGaO(3) anionic conductors. The DFT energetics demonstrate that Ga-V(O)-Ga (V(O) = oxygen vacancy) environments are favored (vs Ga-V(O)-Mg, Mg-V(O)-Mg and Mg-O-Mg-V(O)-Ga) across a range y = 0.0625, 0.125, and 0.25 of fractional Mg contents in LaGa(1-y)Mg(y)O(3-y/2). The results are interpreted in terms of doping and mean phase formation energies (relative to binary oxides) and are compared with previous calculations and experimental calorimetry data. Experimental multinuclear NMR data reveal that while Mg sites remain six-fold coordinated across the range of phase stoichiometries, albeit with significant structural disorder, a stoichiometry-dependent minority of the Ga sites resonate at a shift consistent with Ga(V) coordination, demonstrating that O vacancies preferentially locate in the first anion coordination shell of Ga. The strong Mg-V(O) binding inferred by previous studies is not observed here. The (17)O NMR spectra reveal distinct resonances that can be assigned by using the GIPAW NMR calculations to anions occupying equatorial and axial positions with respect to the Ga(V)-V(O) axis. The disparate shifts displayed by these sites are due to the nature and extent of the structural distortions caused by the O vacancies.     

[M + Fe − 5H]2− peptide ion composition verified by Fourier transform mass spectrometry accurate mass and tandem mass spectrometry analyses

Previously, the unusual ion composition [M + Fe - 5H]2- had been proposed as the major species observed when a gamma-carboxy glutamate-containing glyco-peptide was analyzed with electrospray ionization in the negative ionization mode. The sequence assignment of this highly post-translationally modified peptide was based on the mass analysis using a quadrupole ion trap together with information from both Edman and DNA sequencing. Because there was little precedent for the loss of five protons from a ferric cationized peptide, we utilized Fourier transform mass spectrometry accurate mass and tandem mass spectrometry analyses to verify the peptide ion composition.     

High-ResolutionF MAS andF–Cd REDOR NMR Study of Oxygen/Fluorine Ordering in Oxyfluorides

The ordering of fluoride ions on the anion sites in the oxyfluorides Ba₂WO₃F₄, Ba₂MoO₃F₄, CdWO₃F₂, NaMoO₃F, and K₂NbO₃F has been studied with very fast magic angle spinning¹⁹F NMR.¹⁹F MAS NMR of Ba₂WO₃F₄shows that the fluoride ions are disordered within the four equatorial anion positions on the W–O/F chains, but that the anion positions between the chains are fully occupied by fluorine. No difference in fluoride-ion ordering is observed between samples synthesized under a wide variety of conditions (e.g., hydrothermally at 3 kbar at 800°C, and at 227°C at <2 kbar.) In contrast, fluoride ions in the isostructural compound Ba₂MoO₃F₄are almost completely ordered both between and on the W–O/F chains. Two-dimensional NMR is, however, used to demonstrate that a weak¹⁹F resonance corresponding to ≈0.35% of the total fluoride-ion content is not due to a BaF₂impurity but that it results from a small amount of disorder in the tungsten chains. The fluoride ions order on one site in NaMoO₃F and K₂NbO₃F, consistent with earlier studies. The¹⁹F and¹⁹F–¹¹³Cd REDOR NMR of CdWO₃F₂show that the fluoride ions are ordered on two anion sites, each equidistant from a cadmium ion, in contrast to the isostructural compound CuWO₃F₂where ordering on only one anion site has been proposed. A new model for the structure of CdWO₃F₂is proposed.