Controlling the valence change of sulfur in glass during S K-edge XAFS measurements by conductive coating

Abstract

Sulfur is an important multivalent element for tuning glass properties. Analyzing the valence state of sulfur in glass is essential as it significantly influences the glass characteristics. X-ray absorption fine structure (XAFS) is a powerful technique for elucidating both the valence state and structural attributes of sulfur. However, alterations in the valence of sulfur during XAFS measurements present significant challenges. This study explores a method to control valence changes during S K-edge XAFS measurements. By applying a carbon coating to the surface of glass samples to prevent charging, spectra that accurately reflect the original redox state of sulfur were obtained, which was confirmed by the following: (1) The XAFS spectra of carbon-coated glass samples showed reasonable peak intensities for S²⁻ and S⁶⁺ compared to corresponding standard samples; (2) consistent spectra were obtained from repeated measurements at the same location; and (3) the peak intensity ratio of S²⁻ to the sum of S²⁻ and S⁶⁺ correlated well with the sulfur redox state determined by wavelength-dispersive X-ray fluorescence (WD-XRF). The extended measurement duration permitted by this technique also enabled the detection of small peaks at 2467 and 2469 eV in an amber glass sample, which are related to sulfide-proton (S²⁻–H⁺) and sulfide-ferric (S²⁻–Fe³⁺) bonds, respectively. Utilizing this method in conjunction with synchrotron light sources of increased brightness could further enhance the detection of such minor peaks and provide deeper insight into the structural characteristics of sulfur in glass and their influence on glass properties.