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

Abstract

In situ Ta L3-edge XAS measurements have been made from a Ta (~ 1400 ppm)-bearing peraluminous silicate glass + H2O system to 960 °C and ~ 0.6 GPa. A white-line doublet separated by ~ 4 eV occurs in the Ta L3-edge XANES and results from octahedral crystal field splitting of the Ta 5d levels due to the local structure surrounding Ta coordinated by Qn-species (n = number of bridging oxygen atoms shared between SiO4 and AlO4 units) in the silicate glass/melt + H2O system. The XANES spectra measured from the hydrous silicate glass/melt and from the silicate-rich aqueous fluid have been analyzed using multi-peak fitting techniques. The white-line doublet intensity varies with increasing P-T conditions of the silicate glass/melt + water system, indicating a shift in the electronic density of states in the vicinity of quasi bound Ta 5d states probed by the 2p3/2 core photoelectron. Ab initio modeling of the XANES indicates that water dissolution causes distortion of local structure surrounding the 6-fold coordinated Ta-Qn clusters in the hydrous silicate glass/melt and in the silicate-rich aqueous fluid. Calculation of the angular-momentum projected density of states (l-DOS) shows that the upper doublet level quasi-bound d-DOS is steadily reduced with increasing distortion of the local structure surrounding Ta-Qn clusters.

Department(s)

Physics, Astronomy, and Materials Science

Document Type

Article

DOI

https://doi.org/10.1016/j.jnoncrysol.2013.03.011

Keywords

X-ray absorption, high pressure, silicate glass-melt structure, high field strength elements, water dissolution in silicate melt

Publication Date

2013

Journal Title

Journal of non-crystalline solids

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