Single-crystal elasticity of pyrope and MgO to 20 GPa by Brillouin scattering in the diamond cell

Stanislav V. Sinogeikin, Jay D. Bass

Research output: Contribution to journalArticle

Abstract

The single-crystal elastic properties of synthetic pyrope (Mg3Al2Si3O12) and periclase (MgO) have been measured by Brillouin scattering in a diamond anvil cell (DAC) up to 20 GPa. A 16:3:1 mixture of methanol-ethanol-water was used as a pressure-transmitting medium. Above the freezing pressure of this medium (~ 14 GPa), heat treatment and accompanying stress relaxation produces quasi-hydrostatic conditions. An analysis of geometric errors associated with the DAC indicates that the DAC introduces an additional uncertainty in velocity of ≤ 0.5% (as compared to measurements in air), if there is no vignetting of the incident and scattered beams. The nonhydrostaticity caused by freezing of the pressure-transmitting medium results in lower velocities and elastic moduli than are obtained under hydrostatic conditions, and this leads to an overestimation of the second pressure derivatives of the elastic moduli. Fitting our hydrostatic data to finite-strain equations of state yields the following adiabatic bulk (K(S)) and shear (μ) moduli and their pressure derivatives: K(S) = 163.2(10), K' = 3.96(10), K″ = -0.044(20), μ = 130.2(10), μ' = 2.35(10), μ″ = -0.040(20) for MgO and K(S) = 171.2(20), K' = 4.1(3), μ = 93.7(20), μ' = 1.3(2) for pyrope, where primes indicate pressure derivatives of moduli. Our results for MgO are in excellent agreement with previous ultrasonic measurements performed at lower pressures, and in particular the values of K' agree to within a few percent. Our data are in good agreement with recent compression measurements on pyrope to pressures exceeding 20 GPa, suggesting that Brillouin scattering is an accurate method for high-pressure density and elastic moduli measurements. Pyrope is nearly elastically isotropic at ambient conditions and remains isotropic over the pressure range studied here. In contrast, the elastic anisotropy of MgO is observed to decrease dramatically with increasing pressure, becoming elastically isotropic at ~ 21.5 GPa. (C) 2000 Elsevier Science B.V. All rights reserved.

Original languageEnglish (US)
Pages (from-to)43-62
Number of pages20
JournalPhysics of the Earth and Planetary Interiors
Volume120
Issue number1
DOIs
StatePublished - Jun 2000

Keywords

  • Brillouin spectroscopy
  • Diamond anvil cell
  • Elastic properties
  • Equation of state
  • Mantle mineralogy

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Geophysics
  • Physics and Astronomy (miscellaneous)
  • Space and Planetary Science

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