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Effect of Al³⁺ and H⁺ on the elastic properties of stishovite

Dmitry L. Lakshtanov^1,*, Konstantin D. Litasov², Stanislav V. Sinogeikin^1,, Holger Hellwig¹, Jie Li¹, Eiji Ohtani² and Jay D. Bass¹

¹ Department of Geology, University of Illinois at Urbana-Champaign, 1301 W Green Street, Urbana, Illinois 61801, U.S.A.
² Institute of Mineralogy, Petrology and Economic Geology, Tohoku University, Aza Aoba Aramaki, Sendai 980–8578, Japan

Correspondence: ^* E-mail: lakshtan{at}uiuc.edu

X-ray diffraction, Brillouin, and Raman scattering measurements were performed on Al³⁺ and H⁺-bearing stishovite at ambient conditions. Samples with different Al³⁺ and H⁺ contents were used to examine the effects of these minor constituents on the density, acoustic velocities, single-crystal and aggregate elastic moduli. The X-ray diffraction and compositional data suggest that the incorporation mechanism of Al³⁺ into stishovite involves the formation of oxygen vacancies, in addition to the incorporation H⁺ in the structure. Our data show an overall linear decrease of the acoustic velocities, single crystal (c_ij) and aggregate (K₀, G₀) elastic moduli as a function of Al³⁺ concentrations. For the sample of stishovite containing 6.07(5) wt% Al₂O₃ and 0.24(2) wt% H₂O we obtained: zero-pressure adiabatic bulk modulus, K_S0 = 290(3) GPa, and the shear modulus, G_S0 = 207(2) GPa, with a calculated density of = 4.16(1) g/cm³ based on X-ray diffraction. Stishovite containing 4.37(12) wt% Al₂O₃ and 0.29(3) wt% H₂O possesses higher aggregate moduli: K_S0 = 296(3) GPa and G_S0 = 213(2) GPa, with a calculated density of = 4.21(1) g/cm³ based on X-ray diffraction. We conclude that the formation of oxygen vacancies has a stronger effect on the density and thus elastic properties of stishovite than does the incorporation of hydrogen.

Key Words: Stishovite • elasticity • aluminum • hydrogen • mantle • Brillouin spectroscopy • oxygen vacancies

This article has been cited by other articles:

				D. L. Lakshtanov, S. V. Sinogeikin, K. D. Litasov, V. B. Prakapenka, H. Hellwig, J. Wang, C. Sanches-Valle, J.-P. Perrillat, B. Chen, M. Somayazulu, et al. The post-stishovite phase transition in hydrous alumina-bearing SiO2 in the lower mantle of the earth PNAS, August 21, 2007; 104(34): 13588 - 13590. [Abstract] [Full Text] [PDF]