Showing papers by "Stanislav V. Sinogeikin published in 1999"

Single-crystal elasticity of MgO at high pressure

Abstract: The single-crystal elastic properties of MgO were measured by Brillouin scattering in diamond anvil cell to 18.6 GPa. These measurements demonstrate that quasihydrostatic stress conditions can be obtained in solid pressure medium by thermal annealing, and establish the accuracy with which elastic moduli can be measured over this extensive pressure range (\ifmmode\pm\else\textpm\fi{}5% in ${\mathrm{dC}}_{\mathrm{ij}}/dP).$ The acoustic anisotropy of MgO decreases with pressure, with MgO becoming isotropic at \ensuremath{\sim}21.5 GPa. Deviations from noncentral interatomic forces, as measured by the Cauchy relations, increase steadily with pressure.

Elasticity of MgSiO3 orthoenstatite

Abstract: The single-crystal elastic moduli of the MgSiO 3 orthoenstatite end-member have been measured by Brillouin spectroscopy at ambient conditions. The aggregate elastic moduli at 1 atm are KS = 107.6(15) GPa and μ = 76.8(7) GPa, for the adiabatic bulk modulus and shear modulus, respectively. These values are in excellent agreement with the results of previous acoustic studies of synthetic MgSiO3. Comparison of our results with pressure-volume ( P-V) measurements do not support the presence of a change in the P-V trajectory of orthoenstatite at ~4 GPa, as suggested previously on the basis of X-ray measurements to 8.5 GPa. The effects of chemical composition on the elasticity of orthopyroxenes are well represented by the variation of compressional and shear velocities with density, which exhibit well defined trends for both synthetic and natural samples.

High temperature single crystal properties of mullite

Abstract: Extensive neutron diffraction and Rietveld studies of dense, hot pressed mullite (3Al 2 O 3 ·2SiO 2 ) have been conducted up to 1650 °C in air, yielding a complete set of lattice parameters and axial thermal expansion coefficients. Unconstrained powders of the same stoichiometric composition were also analyzed by X-ray diffraction and Rietveld techniques up to 900 °C in air, from which lattice parameters and thermal expansion coefficients were obtained. An earlier reported structural discontinuity was confirmed by XRD to lie in the temperature range 425 to 450 °C. Single-crystalline mullite fibers of composition 2·5Al 2 O 3 ·SiO 2 were grown from the melt by a laser-heated, float zone method. A partial set of the single-crystal elastic moduli were determined from various sections of fiber, by Brillouin spectroscopy, from room temperature up to 1400 °C. They indicated a roughly 10% reduction in stiffness over that temperature range.

Single-crystal elastic properties of chondrodite: implications for water in the upper mantle

Abstract: Chondrodite, a member of the humite group of minerals, forms by hydration of olivine and is stable over a range of temperatures and pressures that includes a portion of the uppermost mantle. We have measured the single crystal elastic properties of a natural chondrodite specimen at ambient conditions using Brillouin spectroscopy. The isotropic aggregate bulk (K) and shear (µ) moduli calculated from the single-crystal elastic moduli, Cij, are: KS=118.4(16) GPa and µ=75.6(7) GPa. A comparison of the structures and elasticity of olivine and chondrodite indicate that the replacement of O with (OH,F) in M2+O6 octahedra has a small effect on the elasticity of humite-group minerals. The slightly diminished elastic moduli of humite-group minerals (as compared to olivine) are likely caused by a smaller ratio of strong structural elements (SiO4 tetrahedra) to weaker octahedra, and perhaps a more flexible geometry of edge-sharing MO4(O,OH,F)2 octahedra. In contrast to the humite-olivine group minerals, the incorporation of water into garnets and spineloids leads to a more substantial decrease in the elastic properties of these minerals. This contrasting behavior is due to formation of O4H4 tetrahedra and vacant hydroxyl-bearing octahedra in the garnets and spineloids, respectively. Therefore, the mechanism of incorporation of H/OH into mineral phases, not only degree of hydration, should be taken into account when estimating the effect of water on the elastic properties of minerals. The bulk elastic wave velocities of chondrodite and olivine are very similar. If humite-like incorporation of OH is predominant in the upper mantle, then the reaction of OH with olivine will have a minor or possibly no detectable effect on seismic velocities. Thus, it may be difficult to distinguish chondrodite-bearing rocks from “anhydrous” mantle on the basis of seismically determined velocities for the Earth.

Elasticity of MgSiO_3 orthoenstatite

Abstract: The single-crystal elastic moduli of the MgSiO_3 orthoenstatite end-member have been measured by Brillouin spectroscopy at ambient conditions. The aggregate elastic moduli at 1 atm are K_s = 107.6(15) GPa and µ = 76.8(7) GPa, for the adiabatic bulk modulus and shear modulus, respectively. These values are in excellent agreement with the results of previous acoustic studies of synthetic MgSiO_3 . Comparison of our results with pressure-volume (P-V) measurements do not support the presence of a change in the P-V trajectory of orthoenstatite at approximately 4 GPa, as suggested previously on the basis of X-ray measurements to 8.5 GPa. The effects of chemical composition on the elasticity of orthopyroxenes are well represented by the variation of compressional and shear velocities with density, which exhibit well defined trends for both synthetic and natural samples.