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

Mosenfelder, Jed L. and Kim, Namjun and Stebbins, Jonathan F. (2010) Silicon coordination in rutile and TiO_2-II at ambient and high pressures: Si-29 NMR. American Mineralogist, 95 (7). pp. 968-973. ISSN 0003-004X.

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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.

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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.
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Subject Keywords:Crystal structure; rutile; TiO2-II; high-pressure studies; NMR spectroscopy
Issue or Number:7
Record Number:CaltechAUTHORS:20100805-150641099
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:19302
Deposited By: Tony Diaz
Deposited On:05 Aug 2010 22:22
Last Modified:03 Oct 2019 01:55

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