Valence band of tungsten compounds probed using 2p5d RIXS

Marcin Sikora 1Pieter Glatzel 2

1. AGH University of Science and Technology (AGH), al. Mickiewicza 30, Kraków 30-059, Poland
2. European Synchrotron Radiation Facility, Grenoble, France

Abstract

Heavy transition metals of 5d series are important additives in a wide spectrum of industrial applications, due to high melting temperatures, good surface stability, excellent mechanical strength, and corrosion resistance. They are common ingredients in catalytic converters as well as opto- and spin electronics devices.

Electronic structure of the late 5d elements is routinely probed in-situ using X-ray absorption spectroscopy (XAS), due to high sensitivity of the L2,3-edge spectral shape to the occupation of d orbitals. However, in the case of the early 5d elements the XAS spectral changes are less pronounced, due to smaller relative change in the occupation of empty states upon electron transfer, which makes difficult the quantitative analysis. There, X-ray emission spectroscopy (XES), a technique probing density of occupied valence states, is more appropriate. It gives an element and symmetry sensitive insight into the electronic structure of occupied bands. A combination of the two techniques, namely 2p Resonant X-ray Emission Spectroscopy (RXES) and 2p5d Resonant Inelastic X-ray Scattering (RIXS), provide researchers with detailed  information on electronic structure of core levels and valence band, respectively, with bulk sensitivity.

In this contribution we present an overview of the evolution of tungsten electronic structure in a series of tungsten compounds – oxides, carbides, silicates and sulphides – as revealed by RIXS and RXES upon excitation at W L2,3-edge. We observe that electronic structure of core levels, even the shallow ones, is insensitive to the local environment. Also the bandwidth of valence band does not reveal significant differences among the compounds studied, except for WO2 (see Fig.1). However, the intensity and fine structure of the spectra reveal small differences among all the studied compounds, that can be related to local structure and coordination type. The experimental spectra can be nicely reproduced using multiple-scattering approach (FEFF 9 or FDMNES) providing a way for their detailed analysis and leading to potential use of the technique in chemical characterization of a wide class of technologically relevant materials.

Figure 1. Contour plots of the valence band RIXS in WO2 and WO3 probed at W L2-edge.

Acknowledgements: European Synchrotron Radiation Facility, Grenoble, is acknowledged for providing beamtime. MS acknowledges support from Polish Ministry of Science and Higher Education, grants ESRF/73/2006 and N N202 071539.

 

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Presentation: Oral at IX Krajowe Sympozjum Użytkowników Promieniowania Synchrotronowego, by Marcin Sikora
See On-line Journal of IX Krajowe Sympozjum Użytkowników Promieniowania Synchrotronowego

Submitted: 2011-06-15 23:47
Revised:   2011-06-27 16:31