Anomalous sound velocities in polycrystalline MgO under non-hydrostatic compression

Abstract

[1] Brillouin scattering from polycrystalline MgO (periclase) non-hydrostatically compressed to, and decompressed from, 60 GPa at room temperature documents shearand compressional-wave velocities ∼20% lower than values measured under hydrostatic compression. Calculations reveal that wave velocities can be lowered due to the elastic effects of non-hydrostatic stresses, but by only a few percent. Neither these elastic effects nor preferred orientation can account for the reduction in the sound velocity.

Elastic properties of MgO nanocrystals and grain boundaries at high pressures by Brillouin scattering

“…In our experiments at this pressure, we find the uniaxial stress component to be 6 GPa, but observe a reduction of 27% in shear-wave velocities compared to the single-crystal reference 33 . Our direct measurements of deviatoric stresses and sound velocities therefore confirm the previous 35 conclusion that non-hydrostatic effects do not account for the observed reduction in velocities for polycrystalline MgO.…”

“…Our findings provide an explanation for previous Brillouin results on the sound wave velocities of MgO powder compressed under non-hydrostatic conditions, where velocities were found to be anomalously low 35 .…”

“…The potential effect of non-hydrostaticity on acoustic wave velocities in MgO has been discussed previously 35 . Non-hydrostaticity can in principle lead to lower velocities in the plane perpendicular to the maximum principal stress.…”

Deep Earth Structure: Lower Mantle and D″

“…Extensive theoretical and experimental mineral physics research continues to characterize the equations of state, effects of minor components like Al, element partitioning, and physical properties of the following primary lower mantle minerals (or low-pressure analog minerals): magnesium silicate perovskite (e.g., Aizawa and Yoneda, 2006;Andrault et al, 2007;Auzende et al, 2008;Boffa Ballaran et al, 2012;Carrez et al, 2007a;Cordier et al, 2004;Deng et al, 2008;Dorfman et al, 2012;Ferré et al, 2007;Irifune et al, 2010;Ito and Toriumi, 2010;Jackson and Kung, 2008;Jackson et al, 2005;Jung et al, 2010;Katsura et al, 2009;Lundin et al, 2008;Miyajima et al, 2009;Mosenfelder et al, 2009;Murakami et al, 2007a;Nishio-Hamane et al, 2008;Nishiyama et al, 2007;Ono et al, 2006a,b;Panero et al, 2006;Ricolleau et al, 2009;Saikia et al, 2009;Sakai et al, 2009a;Tange et al, 2009Tange et al, , 2012Vanpeteghem et al, 2006a,b;Xu et al, 2011;Yamazaki et al, 2009), MgO and ferropericlase (e.g., de Koker, 2010;Fukui et al, 2012;Gleason et al, 2011;Jackson et al, 2006;Komabayashi et al, 2010;Marquardt et al, 2009b;Murakami et al, 2009;…”

A novel approach to Hugoniot measurements utilizing transparent crystals

“…The physical properties of MgO in the warm dense matter regime are essential in geophysical models. [13][14][15] Third, MgO has been the focus of numerous high-pressure static [16][17][18][19][20][21] and dynamic compression experiments. 12,[22][23][24] The principal Hugoniot has been measured to 199 GPa making it an excellent transparent crystal to examine the experimental technique proposed herein.…”