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Title: First-principles investigation of hydrous post-perovskite

A stable, hydrogen-defect structure of post-perovskite (hy-ppv, Mg 1–xSiH 2xO 3) has been determined by first-principles calculations of the vibrational and elastic properties up to 150 GPa. Among three potential hy-ppv structures analyzed, one was found to be stable at pressures relevant to the lower-mantle D" region. Hydrogen has a pronounced effect on the elastic properties of post-perovskite due to magnesium defects associated with hydration, including a reduction of the zero-pressure bulk (K 0) and shear (G 0) moduli by 5% and 8%, respectively, for a structure containing ~1 wt.% H 2O. However, with increasing pressure the moduli of hy-ppv increase significantly relative to ppv, resulting in a structure that is only 1% slower in bulk compressional velocity and 2.5% slower in shear-wave velocity than ppv at 120 GPa. In contrast, the reduction of certain anisotropic elastic constants (C ij) in hy-ppv increases with pressure (notably, C 55, C 66, and C 23), indicating that hydration generally increases elastic anisotropy in hy-ppv at D" pressures. Calculated infrared absorption spectra show two O–H stretching bands at ~3500 cm –1 that shift with pressure to lower wavenumber by about 2 cm –1/GPa. At 120 GPa the hydrogen bonds in hy-ppv are stillmore » asymmetric. Furthermore, the stability of a hy-ppv structure containing 1–2 wt.% H 2O at D" pressures implies that post-perovskite may be a host for recycled or primordial hydrogen near the Earth’s core-mantle boundary.« less
Authors:
 [1] ;  [2] ;  [1] ;  [1]
  1. Northwestern Univ., Evanston, IL (United States)
  2. Ehime Univ., Ehime (Japan)
Publication Date:
Grant/Contract Number:
NA0002006
Type:
Accepted Manuscript
Journal Name:
Physics of the Earth and Planetary Interiors
Additional Journal Information:
Journal Volume: 244; Journal Issue: C; Journal ID: ISSN 0031-9201
Publisher:
Elsevier
Research Org:
Carnegie Institution of Washington, Washington, D.C. (United States)
Sponsoring Org:
USDOE National Nuclear Security Administration (NNSA)
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; hydrogen; post-perovskite; lower mantle; elasticity
OSTI Identifier:
1335503

Townsend, Joshua P., Tsuchiya, Jun, Bina, Craig R., and Jacobsen, Steven D.. First-principles investigation of hydrous post-perovskite. United States: N. p., Web. doi:10.1016/j.pepi.2015.03.010.
Townsend, Joshua P., Tsuchiya, Jun, Bina, Craig R., & Jacobsen, Steven D.. First-principles investigation of hydrous post-perovskite. United States. doi:10.1016/j.pepi.2015.03.010.
Townsend, Joshua P., Tsuchiya, Jun, Bina, Craig R., and Jacobsen, Steven D.. 2015. "First-principles investigation of hydrous post-perovskite". United States. doi:10.1016/j.pepi.2015.03.010. https://www.osti.gov/servlets/purl/1335503.
@article{osti_1335503,
title = {First-principles investigation of hydrous post-perovskite},
author = {Townsend, Joshua P. and Tsuchiya, Jun and Bina, Craig R. and Jacobsen, Steven D.},
abstractNote = {A stable, hydrogen-defect structure of post-perovskite (hy-ppv, Mg1–xSiH2xO3) has been determined by first-principles calculations of the vibrational and elastic properties up to 150 GPa. Among three potential hy-ppv structures analyzed, one was found to be stable at pressures relevant to the lower-mantle D" region. Hydrogen has a pronounced effect on the elastic properties of post-perovskite due to magnesium defects associated with hydration, including a reduction of the zero-pressure bulk (K0) and shear (G0) moduli by 5% and 8%, respectively, for a structure containing ~1 wt.% H2O. However, with increasing pressure the moduli of hy-ppv increase significantly relative to ppv, resulting in a structure that is only 1% slower in bulk compressional velocity and 2.5% slower in shear-wave velocity than ppv at 120 GPa. In contrast, the reduction of certain anisotropic elastic constants (Cij) in hy-ppv increases with pressure (notably, C55, C66, and C23), indicating that hydration generally increases elastic anisotropy in hy-ppv at D" pressures. Calculated infrared absorption spectra show two O–H stretching bands at ~3500 cm–1 that shift with pressure to lower wavenumber by about 2 cm–1/GPa. At 120 GPa the hydrogen bonds in hy-ppv are still asymmetric. Furthermore, the stability of a hy-ppv structure containing 1–2 wt.% H2O at D" pressures implies that post-perovskite may be a host for recycled or primordial hydrogen near the Earth’s core-mantle boundary.},
doi = {10.1016/j.pepi.2015.03.010},
journal = {Physics of the Earth and Planetary Interiors},
number = C,
volume = 244,
place = {United States},
year = {2015},
month = {4}
}