First principles investigation of the structural and elastic properties of hydrous wadsleyite under pressure
First principles investigation of the structural and elastic properties of hydrous wadsleyite under pressure
复制标题
DOI：
10.1029/2008jb005841
复制
发表时间：
2009-02
影响因子：
--
通讯作者：
J. Tsuchiya;T. Tsuchiya
中科院分区：
文献类型：
--
作者：
J. Tsuchiya;T. Tsuchiya
[1]为了阐明高压条件下硅镁石质子化的影响，我们测定了Mg1.875SiO4H0.25的缺陷结构（1 Mg 2+参与2- Mg +2 H+，1.65wt%H2O），Mg 1.75SiO4H0.5（2 Mg 2+ Particip 2 V2- Mg +4 H-，3.3wt%H2O）水化硅铝石及其弹性性质.结构优化计算表明，最稳定的结构具有单斜对称性与镁M3位空位。质子被发现键合到O 1网站对齐的OH偶极子沿着边缘的M3空位。计算出的弹性常数，体积和剪切模量，发现几乎线性减少，随着含水量的增加，但线性增加，随着压力。在15 GPa和静态0 K条件下，加入3.3wt%的H2O（相当于水化硅铝石的最大溶解度）使Vp和Vs分别降低3.9%和4.8%。这表明1wt%H2O水化过程对应的温度效应分别为430 K（0 GPa）~ 340 K（20 GPa）和350 K（0 GPa）~ 290 K（20 GPa）。横向各向同性聚集体表现出最大的正极化各向异性V SH-V SV时，c轴垂直对齐，在干燥和潮湿的情况下。
[1] 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 2- Mg + 2H + , 1.65 wt % H 2 O), Mg 1.75 SiO 4 H 0.5 (2Mg 2+ ↔ 2V 2- Mg + 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 Vp 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.