Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (7) Citing Articles via Google Scholar Google Scholar Articles by Stebbins, J. F. Articles by Ono, S. Search for Related Content GeoRef GeoRef Citation

Aluminum substitution in stishovite and MgSiO₃ perovskite: High-resolution ²⁷Al NMR

¹ Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305-2115, U.S.A.
² Department of Chemistry, Faculty of Science, Gakushuin University, 1-5-1 Mejiro, Toshima-ku, Tokyo 171-8588, Japan
³ Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka-shi, Kanagawa 237-0061, Japan

Correspondence: ^* E-mail: Stebbins{at}pangea.stanford.edu

Aluminum is an important minor constituent of a number of high-pressure mantle silicates in which it substitutes for octahedrally coordinated silicon. In several cases, its solid solution may be linked to the presence of oxygen vacancies; in others, to charge balance with H⁺. Here we present new data from high-resolution, high-field (18.8 Tesla) ²⁷Al NMR of aluminous stishovite and of a non-stoichiometric perovskite with nominal composition MgSi_0.95Al_0.05O_2.975. For the stishovite, we characterize the local structure of the symmetrical, octahedral site for Al. These results, combined with ²⁷Al{¹H} REDOR NMR, are consistent with hypothesized H⁺ charge balance, although the presence of a significant fraction of randomly distributed oxygen vacancies could remain undetected. As in a recent previous study of a related perovskite composition, the observed ratio of Al at symmetrical octahedral B sites to that of Al at large, central A sites is about 2:1, indicating the presence of oxygen vacancies to account for charge neutrality in this phase. Such vacancies are not preferentially associated with the Al octahedra, however, suggesting a random distribution in the structure.

Key Words: High-pressure studies • perovskite • stishovite • NMR spectroscopy • crystal structure • phase equilibria

This article has been cited by other articles:

				A. Ricolleau, G. Fiquet, A. Addad, N. Menguy, C. Vanni, J.-P. Perrillat, I. Daniel, H. Cardon, and N. Guignot Analytical transmission electron microscopy study of a natural MORB sample assemblage transformed at high pressure and high temperature American Mineralogist, January 1, 2008; 93(1): 144 - 153. [Abstract] [Full Text] [PDF]

				N. Kim, J. F. Stebbins, S. Quartieri, and R. Oberti Scandium-45 NMR of pyrope-grossular garnets: Resolution of multiple scandium sites and comparison with X-ray diffraction and X-ray absorption spectroscopy American Mineralogist, November 1, 2007; 92(11-12): 1875 - 1880. [Abstract] [Full Text] [PDF]

				F. Brunet, A.-M. Flank, J.-P. Itie, T. Irifune, and P. Lagarde Experimental evidence of sixfold oxygen coordination for phosphorus American Mineralogist, July 1, 2007; 92(7): 989 - 993. [Abstract] [Full Text] [PDF]