Z. Wu

Improved hydrogen storage properties of LiBH4 destabilized by carbon

The hydrogen storage properties of LiBH4 ball milled with various ratios of carbon nanotubes (Cnano) were investigated. The LiBH4∕Cnano mixtures showed superior dehydrogenation, hydrogen desorption starting at 250°C, and the majority of hydrogen being released below 600°C. The rehydrogenation results revealed that the Li2C2, formed during the dehydrogenation, could be reversed to LiH, in which the hydrogen capacity corresponds to 1∕4 of the original hydrogen content of LiBH4, and C at 10MPa hydrogen pressure and 400°C.

Symmetry dependence of x-ray absorption near-edge structure at the metal K edge of 3d transition metal compounds

The pre-edge features in a system with even symmetry, apart from quadrupolar transition contribution, are mainly dipolar in character, associated with the existence of unoccupied states made up of mixed cation np with higher-neighboring cation- (n-1) d orbitals, and reflect the density of states due to the medium-range order of the system, while in odd symmetry materials these pre-edge features are the result of a transition from the Is to a final density of states of p symmetry due to an unsymmetrical mixing of the ligand wave functions with the central cation d orbitals. In the latter case, they contain not only the p but also the d base of orbitals, similar to a tetrahedral configuration. These results are validated for Fe as a photoabsorber by comparing x-ray absorption near-edge spectra of Fe2SiO4 (fayalite) and Fe2O3 (hematite) to ab initio full multiple scattering calculations at the Fe K edge, but pertain to all systems containing sixfold-coordinated cations

Application of multiple scattering calculation to the study of local geometry in silicate glasses of geological interest

Abstract Multiple scattering calculations have been used to study the effects of coordination number, geometry, symmetry and polyhedral distortion on the titanium XANES spectra. The calculations show the influence of each parameter to the Ti K-edge XANES spectra and in particular how the polyhedral distortion affects the spectrum. The small clusters used for the calculations represent some possible geometries of titanium atoms in silicate glasses, where Ti is coordinated by oxygen and is found to be in different geometrical environments, mainly as a function of glass composition.

Oxygen–metal bonding in Ti-bearing compounds from O 1s spectra and ab initio full multiple-scattering calculations

The O K-edge spectra of a series of Ti-bearing compounds with Ti in different structural and chemical environments have been measured using electron energy-loss spectroscopy and analyzed using ab initio full multiple-scattering (MS) calculations. The near-edge structures arise mainly from covalency by direct and/or indirect interaction between O and metal atoms and between O and Si atoms. The coordination number of the cation and the site symmetry also influence the spectral shape and structures. Using different size clusters around the excited atom in the full MS simulation, it is possible to interpret and assign the features present in the spectra of each compound to its specific atomic arrangement and electronic structure.

Detection of order-disorder in pyroxenes of the jadeite-diopside series via XAS at the CaNa and MgAl K-Edges

Abstract Soft X-ray absorption spectroscopy studies have been carried out on a number of natural clinopyroxenes of different origin straddling the compositional join between diopside and jadeite with only minor substitutions of Fe 2+ for Mg, and of Fe 3+ for Al. Calculation of the spectra is successfully made by the program package developed by C.R. Natoli and his coworkers, which is based on the multichannel multiple scattering formalism.

Symmetry role on the preedge X-ray absorption fine structure at the metal K-edge

The preedge features in a system with even symmetry, apart from quadrupolar transition contribution, are mainly dipolar in character, associated with the existence of unoccupied states made up of mixed cation-4p with higher-neighboring cation-3d orbitals, and reflect the density of states due to the medium-range order of the system. In odd symmetry materials these preedge features are the result of a transition from the 1s to a final density of states of p symmetry due to an unsymmetrical mixing of the ligand wave functions with the central cation 3d orbitals, similar to atetrahedral configuration. These results are validated for Fe as a photoabsorber by comparing XAS spectra of Fe2SiO4 (fayalite) to ab initio full multiple scattering calculations at the Fe K edge, but pertain to all systems containing sixfold-coordinated cations.