Pressure-induced structural changes and densification of vitreous MgSiO3

Evidence of denser MgSiO3glass above 133 gigapascal (GPa) and implications for remnants of ultradense silicate melt from a deep magma ocean

“…2), it is reasonable to expect that the gradual change in Si-O coordination number from four-to sixfold in MgSiO 3 glass is continuous over a broad pressure range up to approximately 130 GPa. This is possibly due to the presence of network-modifying Mg 2þ cations acting to impede the Si-O coordination change from 4 → 6, at least at lower pressures (13,14). Such a gradual coordination change over a broad pressure range is consistent with recent computational simulations on MgSiO 3 melt using first-principles molecular dynamics (25).…”

“…Although measurements on silicate melts at high pressures are beyond current experimental capabilities, MgSiO 3 glass can be used as an analogue for the most abundant component of the silicate melts in a deep magma ocean (12). Experimental investigations of the high-pressure structure of the MgSiO 3 glass up to a pressure of 39 GPa strongly suggest that changes in the Si-O and Mg-O coordination number are a critical to the densification mechanism of MgSiO 3 glass (13,14). However, little is known about further densification above approximately 40 GPa due to experimental challenges and the lack of suitable in situ structural probes.…”

Structural organisation in oxide glasses from molecular dynamics modelling

“…expected bQ n N = Q 0 ), where some excess oxygen might be expected. The result is supported by NMR observations [31] which are reproduced in Fig. 6, in which article it was reported "the lower frequency shoulder in the 29 Si MAS NMR... is primarily a characteristic of Q 3 species".…”

“…6. 29 Si NMR chemical shift spectrum reported for 50MgO·50SiO 2 glass [31]. The spectrum has been fitted (dotted line) with two Gaussians (dashed lines) at − 81 ppm and − 100 ppm, consistent with Q 2 and Q 3 groups, with relative areas of 78% and 22% (respectively).…”

Aluminum coordination in rhyolite and andesite glasses and melts: Effect of temperature, pressure, composition and water content

“…However, the low natural abundance of 29 Si (4.7%) and the long T1 relaxation times (up to 7 h for pure SiO 2 glass ), result in exceedingly long acquisition times to obtain spectra with signal-to-noise ratios sufficiently high to detect and quantify traces of higher coordinated Si. Nevertheless, [5] Si and [6] Si has been observed, both for samples synthesized at atmospheric and elevated pressure and both for samples enriched in 29 Si and for natural abundance samples (Xue et al, 1989(Xue et al, , 1991Stebbins and McMillan, 1993;Gaudio et al, 2008;Kelsey et al, 2009a). The trends observed in these studies indicate that most, but perhaps not all, Si will be in fourfold coordination for our investigated pressure range (up to 3.5 GPa), while more substantial amounts of higher coordinated Si (>1%) will occur at higher pressures only.…”