
First principles investigation of the structural and elastic properties of hydrous wadsleyite under pressure
Author(s) -
Tsuchiya Jun,
Tsuchiya Taku
Publication year - 2009
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2008jb005841
Subject(s) - materials science , elastic modulus , bulk modulus , anisotropy , transverse isotropy , shear modulus , shear (geology) , mineralogy , analytical chemistry (journal) , crystallography , chemistry , composite material , physics , chromatography , quantum mechanics
In order to clarify the effect of protonation of wadsleyite under high‐pressure conditions, we determined defect structures of Mg 1.875 SiO 4 H 0.25 (1Mg 2+ ↔ V Mg 2− + 2H + , 1.65 wt % H 2 O), Mg 1.75 SiO 4 H 0.5 (2Mg 2+ ↔ 2V Mg 2− + 4H − , 3.3 wt % H 2 O) hydrous wadsleyite and their elastic properties by means of the density functional first principles method. Structural optimization calculations indicate that the most stable structures have monoclinic symmetry with magnesium M3 site vacancies. Protons are found to bond to the O1 site to align the OH dipoles along the edges of M3 vacancies. Calculated elastic constants, bulk and shear moduli, are found to decrease almost linearly with increasing water content but to increase linearly with increasing pressure. At 15 GPa and static 0 K condition, incorporation of 3.3 wt % H 2 O into wadsleyite, which corresponds to the maximum solubility of hydrous wadsleyite, reduces V P and V S by about 3.9 and 4.8%, respectively. This indicates that 1 wt % H 2 O hydration of wadsleyite corresponds to the temperature effects on bulk and shear moduli about 430 K (0 GPa) to 340 K (20 GPa) and 350 K (0 GPa) to 290 K (20 GPa), respectively. The transversely isotropic aggregates demonstrate largest positive polarization anisotropy V SH − V SV when the c axis aligns vertically in both dry and wet cases.