X-ray absorption spectroscopy of strongly disordered glasses: Local structure around Ag ions ing−Ag2O∙nB2O3

Abstract

The local structure around Ag ions in silver borate glasses g-Ag 2 O·nB 2 O 3 ͑n =2,4͒ was studied by x-ray absorption spectroscopy at the Ag K edge for temperatures from 77 to 450 K. Extended x-ray absorption fine structure ͑EXAFS͒ analysis based on cumulant expansion or multishell Gaussian model fails for these systems. Therefore, the radial distribution functions ͑RDFs͒ around Ag ions were reconstructed using a method based on the direct inversion of the EXAFS expression. The RDFs consist of about eight atoms ͑oxygens and borons͒, exhibit a relatively weak temperature dependence, and indicate the presence of strong static disorder. Two main components can be identified in RDFs, located at about 2.3-2.4 Å and 2.5-3.4 Å, respectively. The chemical types of atoms contributing to the RDF were determined via a simulation of configurationally averaged x-ray absorption near-edge structure ͑XANES͒ and EXAFS signals. The immediate neighborhood of Ag contains mostly oxygens while borons dominate at larger distances. The combination of EXAFS and XANES techniques allowed us to determine a more complete structural model than would be possible by relying solely on either EXAFS or XANES alone.

Investigation of the structural environment of Ta in a silicate glass and water system under high P–T conditions

“…The limitations of quantitative analysis of EXAFS measured from highly-disordered systems, including glasses and melts, have been reviewed extensively [12][13][14][15][16]. A self-consistent approach to the analysis of disordered systems includes the use of a theoretical EXAFS function that has a basis in the partial radial distribution functions (known a priori) involving the target and constituent atoms of the material.…”

XAS and XRF investigation of an actual HAWC glass fragment obtained from the Karlsruhe vitrification plant (VEK)

“…Studies on glass materials have been systematically used by, e.g., the group of Fornasini and Dalba to demonstrate the strength of XAFS to reveal bonding properties like non-Gaussian pair distributions in disordered systems (cf. [17] and references therein). XAFS studies have been focused both on network forming glass constituents (such as boron, e.g.…”

On the neglecting of higher-order cumulants in EXAFS data analysis

“…As expected, a decrease (or increase) of the coordination number, if neglected, leads to an increase (or decrease) of the second cumulant, according to the amplitude of the EXAFS signal. This is particularly important in EXAFS studies of glasses or disordered systems, where coordination number and Debye-Waller factor play a key role(Kuzmin et al, 2006; research papers…”