Elastic, vibrational, and thermodynamic properties of MgGeO₃ postperovskite investigated by first principles simulation

Abstract

[1] Elastic, vibrational and thermodynamic properties of MgGeO 3 perovskite (Pv) and postperovskite (PPv) were calculated based on the density functional first principles methods. We found that the calculated properties of MgGeO 3 are quite similar to those of MgSiO 3 in particular for anomalously large c 66 and small c 55 of PPv, but not fully comparable in particular for the velocity contrasts across the phase change, which are all negative in compressional, shear and bulk velocities at the transition pressure unlike the typical features of the D 00 seismic discontinuity. MgGeO 3 PPv has larger elastic anisotropy than MgSiO 3 , but their style is quite similar. Significant orientational preference is needed for PPv polycrystalline aggregate to reproduce seismic shear wave polarization anisotropy observed in D 00 except for a case with the c direction aligned vertically. Lattice dynamics calculations indicate that the both phases are vibrationally stable under high pressure, and quasi-harmonic thermodynamics provides the Clapeyron slope of PPv phase boundary of $+7.8 MPa/K, which is quite comparable to that reported for MgSiO 3 . While the calculated Raman frequencies are in excellent agreement with experimental values in Pv, those are found less consistent in PPv.Citation: Usui, Y., J. Tsuchiya, and T. Tsuchiya (2010), Elastic, vibrational, and thermodynamic properties of MgGeO 3 postperovskite investigated by first principles simulation,

Lattice dynamics and thermodynamic properties of (Mg,Fe2+)SiO3postperovskite

“…Phonons of SiO 2 phases: stishovite, CaCl 2 , and α ‐PbO 2 and phonons of Al 2 O 3 phases: corundum, Rh 2 O 3 (II), and postperovskites were also reported by Tsuchiya et al [2004b, 2005b]. Recently, Tsuchiya and Tsuchiya [2007] and Usui et al [2010] reported the vibrational and thermodynamic properties of MgGeO 3 postperovskite, a lower pressure analog of MgSiO 3 postperovskite within the same technique. Nevertheless, the effects of chemical composition on the vibrational and thermodynamic properties of minerals have not been investigated to date.…”

Deep Earth Structure: Lower Mantle and D″

“…Numerous studies have used stable low-pressure mineral forms such as CaIrO 3 , MnGeO 3 , MgGeO 3 , CdGeO 3 , and CaRuO 3 and NaCoF 3 , NaMgF 3 , and NaNiF 3 as analogs for characterizing the postperovskite transition and deformational properties under relatively accessible (for both laboratory and computations) P-T conditions (e.g., Boffa Ballaran et al, 2007;Cheng et al, 2010Cheng et al, , 2011Dobson et al, 2011;Hirose et al, 2005bHirose et al, , 2010Hunt et al, 2009;Hustoft et al, 2008a,b;Kojitani et al, 2007a,b;Martin et al, 2006aMartin et al, ,b, 2007aMetsue et al, 2009;Miyagi et al, 2008;Miyajima et al, 2006Miyajima et al, , 2010Niwa et al, 2007Niwa et al, , 2011Niwa et al, , 2012Runge et al, 2006;Shim et al, 2007;Stolen and Tronnes, 2007;Tateno et al, 2006Tateno et al, , 2010Tsuchiya and Tsuchiya, 2007;Umemoto et al, 2006;Usui et al, 2010;Walte et al, 2007;Wu et al, 2011).…”

High resolution three‐dimensional X‐ray diffraction study of dislocations in grains of MgGeO3 post‐perovskite at 90 GPa

“…Stresses in the grains were calculated using the strain tensor we obtained, Hooke's law, and the elastic constants of MgGeO 3 ‐pPv [ Usui et al , 2010]. Figure 6 shows the resulting locations of the center of mass of the indexed grains.…”

“…We calculated the theoretical contrast factors on the basis of the crystallography of dislocations [ Borbély et al , 2003], extended to the orthorhombic system [ Cordier et al , 2004; Nyilas et al , 2006], using the elastic constants of MgGeO 3 post‐perovskite at 80 GPa [ Usui et al , 2010]. Numerical values of the theoretical contrast factors for all dislocation types we studied are listed in Table 2.…”