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Published July 2010 | public
Journal Article

Silicon coordination in rutile and TiO_2-II at ambient and high pressures: Si-29 NMR

Abstract

The structural environment of silicon dissolved in rutile and α-PbO_2-structured TiO_2 (TiO_2-II) was probed using ^(29)Si MAS NMR on ^(29)Si-enriched samples. At 1 atm, about 0.01 wt% SiO_2 is incorporated into TiO_2 as ^(IV)Si, presumably in interstitial sites. Rutile recovered from 6 GPa, 1600 °C contains about 0.6 wt% SiO_2, incorporated both as ^(VI)Si (~90%) and ^(IV)Si (~10%). TiO_2-II, synthesized at 12 GPa, 1200 °C, contains only ^(VI)Si. The chemical shift for ^(VI)Si in TiO_2-II is slightly less negative than that for rutile, and the peak is split, suggesting either a more complex mechanism of substitution or a different response to quenching or decompression in the lower-symmetry structure. Future thermodynamic studies of the TiO_2-SiO_2 solid solution will have to take into account the mixed coordination environment of the Si in TiO_2, at low pressures.

Additional Information

© 2010 Mineralogical Society of America. This work was supported by the NSF, grant no. EAR-04-08410 to J. Stebbins. We thank Edward Stolper and Paul Asimow for discussions that inspired us to conduct this study. Brian Balta graciously helped with EPMA. We are grateful for the helpful comments of two anonymous reviewers.

Additional details

Created:
August 22, 2023
Modified:
October 20, 2023