Local Structures around Si, Al and Na in Hydrated Silicate Glasses

Abstract

International audienceXANES spectra were collected at the Si-, Al-, and Na K-edge in hydrous silicate glasses to understand the effect of water on the local structure around these cations. Around network forming Si and Al, no drastic changes are observed. Around Na, the dissolution of water creates more ordered environments in Al-bearing glasses and less ordered environment in Al-free glasses. Ab-initio XANES calculations were undertaken to understand the structural origins for these features. Based on these results, a bond valence model was refined that considers not only the present XANES experiments and models but also NMR information. The double percolation model refined explains, among others, the explosive properties of water-bearing hydrous melts, at the origin of a number of cataclysmic eruptions in subduction zones

Ge coordination inNaAlGe3O8glass upon compression to 131 GPa

“…The charge difference between Al and Ge leads to a longer mean bond length for Al-O due to its lower bond strength according to the bond strength theory [41]. Similarly, a significantly larger mean bond length for Na compared to Ge-O can be considered due to its higher coordination number [45]. In contrast to Ge-O, the nonbonded Ge …Ge distance shows only little shortening at pressures beyond the completion of the octahedral coordination (Fig.…”