Spectroscopic evidence for pressure-induced coordination changes in silicate glasses and melts

Details Spectroscopic evidence for pressure-induced coordination changes in silicate glasses and melts Spectroscopic evidence for pressure-induced coordination changes in silicate glasses and melts

Feb 1988

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1988sci...239..902w&link_type=abstract

Science (ISSN 0036-8075), vol. 239, Feb. 19, 1988, p. 902-905. NSF-supported research.

Computer Science

166

Amorphous Silicon, High Pressure, Infrared Spectra, Melts (Crystal Growth), Oxygen Ions, Silica Glass, Absorption Spectra, Room Temperature, Shock Waves

Scientific paper

Infrared spectra demonstrate that at pressures above 20 gigapascals and room temperature the regular tetrahedral coordination of oxygen around both silicon and aluminum ions is severely disrupted in SiO2, CaMgSiO6, and CaAlSi2O8 composition glasses. The spectra are consistent with gradual, pressure-induced increased in the coordination numbers of silicon and aluminum. A variety of coordination environments, from six-fold to four-fold, appears to be present at pressures as high as about 40 gigapascals. This apparent change in coordination is not quenchable at room temperature: on decompression, the glasses return to tetrahedral coordination. This continuous and reversible coordination change in amorphous silicates explains the lack of observation of coordination changes in silicate glasses quenched from high pressure, the shallow melting slopes observed for mantle silicates at high pressures, and the possible presence of neutrally buoyant magmas deep within the terrestrial planets.

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