X-ray absorption spectroscopic study of a hot pressed MgB2

X-ray near edge absorption spectra (XANES) of boron and oxygen K edge of a hot-pressed MgB₂ (HP2) sample were measured by using synchrotron radiation. The HP2 was produced by annealing a commercial powder of MgB₂ in ambient air under a hydrostatic pressure of 2.0 GPa at 900 °C. No substantial change of the electronic structure in HP2 was observed as indicated in the B K-edge XANES. This sample maintains high superconductivity and enhances the critical current density. The XANES and the XRD combined indicate that both MgO and B₂O₃ in HP2 increase and more B₂O₃ than MgO was produced during the hot-press process. The better connection of the grain in HP2 can be the major cause to increase its critical current density. However, the impurity may also increase the flux pinning and therefore increases the current density.     

X-ray spectroscopic study of cobalt-zinc ferrites

K-absorption edges and the associated fine structures of cobalt and iron in cobalt-zinc ferrites of composition, Zn_xCo_1-xFe₂O₄ (x = 0, 0.25, 0.50 and 0.75) have been recorded employing a 40cm curved crystal spectrograph of transmission type. It is found that the cobalt and iron ions in these samples exist in valence states two and three respectively. Bond lengths have been determined using the X-ray fine structure methods. It is noted that estimated bond lengths are close to those obtained from crystallographic data. It is pointed out that the X-ray fine structure methods can be used to complement diffraction methods for the determination of bond lengths in samples containing atoms of nearly equal scattering power.     

X-ray Photoelectron Spectroscopy of Sb2S3 Crystals

The paper presents the X-ray photoelectron spectra (XPS) of the valence band and core levels of semiconductor ferroelectric Sb₂S₃ single crystals, which show weak phase transitions and anomalies of various physical properties. The XPS were measured with monochromatized Al K _α radiation in the energy range 0-1450 eV and the temperature range 160-450 K. The valence band is located 0.8-7.5 eV below the Fermi level. Experimental results of the valence band and core levels are compared with the results of theoretical ab initio calculations of the molecular model of Sb₂S₃ crystal. The chemical shifts in Sb₂S₃ crystal for the Sb and S states are obtained. Results revealed that the small structural rearrangements at the phase transition T _c1 = 300 K shift the Fermi level and all electronic spectrum. Also, temperature dependence of a spontaneous polarisation shifts the electronic spectra of the valence band and core levels. Specific temperature-dependent excitations in Sb 3d core levels are also revealed.     

Photoelectron spectroscopic studies of the butylbenzenes

The He(I) photoelectron spectra of the geometrical isomers of butylbenzene have been compared. All the isomers have first ionization potentials within 0.08 eV but show variations in the higher ionization energy range. A valence-electron-only model potential (VEOMP-3G) method is employed to aid in the spectral assignment. Comparison with the spectra of benzene and the butyl moiety indicates that the spectra of the butylbenzenes can be interpreted according to a composite-molecule model, which indicates that CC as well as CH hyperconjugation must be invoked to adequately describe the benzene—butyl interactions.     

X-ray spectroscopic study of zirconium and molybdenum diselenides

The K absorption spectra of zirconium, molybdenum and selenium in ZrSe₂ and MoSe₂ have been recorded photographically using a Cauchois type bent crystal (mica) spectrograph. The absorption edge shifts are used along with the data for NbSe₂ (Bhide and Bahl 1971J. Phys. Chem. Solids 32 1001) to propose bond schemes for these compounds.     

X-ray photoelectron spectroscopy of CeO2–Na2O–SiO2 glasses

A series of (CeO₂)_x–(Na₂O)_0.3–(SiO₂)_(0.7−x) glasses, where 0.025 ≤ x ≤ 0.075, have been synthesized and investigated by mean of X-ray photoelectron spectroscopy (XPS). The Ce 3d spin-orbit doublet was curve fitted in order to quantify the proportions of each cerium oxidation state in these glasses. It was found that Ce ions are predominantly in the Ce(III) state in glasses with compositions x ≤ 0.075, while mixed Ce valences were found in the glass with composition x = 0.10. The O 1s spectra have also been curve fitted with two components, one from bridging oxygen (BO) and the other from non-bridging oxygen atoms (NBO). The measured number of NBO, based on the fact that only oxygen atoms in the site Si–O–Na⁺ contribute to the NBO peak, was found to be constant at ∼35% for all samples, in good agreement with the value calculated from the glass composition and inductively coupled plasma (ICP) suggesting that Ce ions enter the network as a glass intermediate. The thermal measurements done on these glasses agree well with the XPS findings.     

X-ray Raman spectroscopic study of water in the condensed phases

Oxygen K-edge x-ray absorption spectra of high-density amorphous (HDA) ice, low-density amorphous ice Ic, ice Ih, normal and deuterated liquid water were measured with the synchrotron x-ray Raman scattering method under almost identical experimental conditions by in situ heating of an HDA ice sample. The distinct preedge structure previously reported in water was observed in all the spectra. The results show that core-hole excitations are localized and not strongly affected by the local environment. Therefore, the existence of the preedge feature is not a concise indicator of the magnitude of local disorder within the hydrogen bonded network. The intensity of the near-edge absorption shifts into the postedge region when the hydrogen bond network becomes more ordered. This observation is interpreted as an enhancement of Wannier over Frenkel excitations in an ordered crystal.     

Soft X-ray spectroscopic study of a gas-puff Z-pinch argon plasma

X-ray radiation characteristics of argon plasma produced by a gas-puff Z-pinch device were investigated using an X-ray crystal spectrometer, an X-ray diode, and an extreme ultraviolet (XUV) spectrometer. Using a germanium crystal we have observed spectral emission from Ar XVII produced by hot spots at the pinched stage. With the help of a 2-m grazing incidence XUV spectrometer, the spectrum of 30 to 250 Å were obtained. Strong lines from Ar VIII to Ar XIII were observed with a continuum whose peak is around 120 Å. The radiation energy in the spectral range is estimated to be about 23 joule which is about 0.6% of the electrical energy stored in capacitors     

Photoelectron spectroscopic assignment of the p-states of benzenethiol

He(I) anisotropy parameters and He(I)/He(II) relative band intensities have been determined and utilised to make a complete assignment of the benzenethiol p-electron-region photoelectron spectrum. The major S-atom contribution appears more so in the third band than in the first.     

Photoelectron spectroscopic characterization of vapors over heated alkali metaborate solids

The He(I) photoelectron spectra of the gaseous metaborates of K, Rb, and Cs have been obtained using a modified high-temperature cylindrical-mirror electron spectrometer equipped with a resistance-heated sample oven. Attempts to acquire data for LiBO₂ and NaBO₂ were unsuccessful because of the high temperature required for volatilization (on the order of 1300–1400 K). The identities of the vapor-phase molecules were based on mass spectrometric and electron diffraction data. Spectral lines were assigned molecular-orbital origins through the use of MO calculations and by analogy with other compounds of similar type.     

Photoelectron spectroscopic study of Li oxides on Li over-deposited V2O5 thin film surfaces

The Li oxides species formed on Li over-deposited V₂O₅ thin film surfaces have been studied by using X-ray and UV induced photoelectron spectroscopy (XPS and UPS). The photoelectron spectroscopic data show that the Li over-deposited V₂O₅ system itself is not stable. Further chemical decomposition reactions are taken place even under UHV conditions and lead to form Li₂O and Li₂O₂ compounds on the surface. The formation of Li₂O₂ causes to arise an emission line at about 11.3 eV in the valence band spectra.     

Oxygen reduction reactions in the SOFC cathode of Ag/CeO2

The interactions between oxygen molecules and a silver surface or a CeO₂(111) supported atomic layer of silver are predicted using first-principles calculations based on spin polarized DFT with PAW method. The juncture between the CeO₂(111), the atomic layer of silver, and O₂ represents a triple-phase boundary (TPB) whereas the interface between silver surfaces and O₂ corresponds to a 2-phase boundary (2PB) in a solid oxide fuel cell (SOFC). Results suggest that the O₂ dissociation process on a monolayer of silver supported by CeO₂(111) surfaces (or TPB) with oxygen vacancies has lower reaction barrier than on silver surfaces (or 2PB), and the dissociated oxygen ions can quickly bond with subsurface Ce atom via a barrierless and highly exothermic reaction. The oxygen vacancies at TPB are found to be responsible for the lower energy barrier and high exothermicity because of the strong interaction between subsurface Ce and adspecies, implying that oxygen molecules prefer being reduced at TPB than on silver surfaces (2PB). The results suggest that, for a silver-based cathode in a SOFC, the adsorption and dissociation of oxygen occur rapidly and the most stable surface oxygen species would be the dissociated oxygen ion with − 0.78|e| Bader charges; the rate of oxygen reduction is most likely limited by subsequent processes such as diffusion or incorporation of the oxygen ions into the electrolyte.