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| Home > Publications database > Synthesis, structure refinement and single-crystal elasticity of Al-bearing superhydrous phase B |
| Typ | Amount | VAT | Currency | Share | Status | Cost centre |
| Hybrid-OA | 3096.35 | 0.00 | EUR | 98.52 % | (Zahlung erfolgt) | 82102 / 476150 |
| Other | 46.45 | 0.00 | EUR | 1.48 % | (Zahlung erfolgt) | 82102 / 476150 |
| Sum | 3142.80 | 0.00 | EUR | |||
| Total | 3142.80 |
| Journal Article | PUBDB-2021-03999 |
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2021
GeoScienceWorld
Alexandria, Va.
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Please use a persistent id in citations: doi:10.2138/am-2022-7989 doi:10.3204/PUBDB-2021-03999
Abstract: Dense hydrous magnesium silicates (DHMSs) with large water content and wide stability fields are a potential H2O reservoir in the deep Earth. Al-bearing superhydrous phase B (shy-B) with a wider stability field than the Al-free counterpart can play an important role in understanding H$_2$O transport in the Earth’s transition zone and topmost lower mantle. In this study, a nominally Al-free and two different Al-bearing shy-B with 0.47(2) and 1.35(4) Al atoms per formula unit (pfu), were synthesized using a rotating multi-anvil press. The single-crystal structures were investigated by X-ray diffraction (XRD) complemented by Raman spectroscopy, and Fourier-transform infrared spectroscopy (FTIR). Single-crystal XRD shows that the cell parameters decrease with increasing Al-content. By combining X-ray diffraction and spectroscopy results, we conclude that the Al-poor shy-B crystallizes in the Pnn2 space group with hydrogen in two different general positions. Based on the results of the single crystal X-ray diffraction refinements combined with FTIR spectroscopy, three substitutions mechanisms are proposed: 2 Al$^{3+}$ = Mg$^{2+}$ + Si$^{4+}$; Mg$^{2+}$ ☐$^{Mg2+}$ + 2H$^+$ (☐$^{Mg2+}$ means vacancy in Mg site); ; Si$^{4+}$ = Al$^{3+}$ + H$^+$. Thus, in addition to the two general H positions, hydrogen is incorporated into the hydrous mineral via point defects. The elastic stiffness coefficients were measured for the Al-shy-B with 1.35 pfu Al by Brillouin scattering (BS). Al-bearing shy-B shows lower C$_{11}$, higher C$_{22}$ and similar C$_{33}$ when compared to Al-free shy-B. The elastic anisotropy of Al-bearing shy-B is also higher than that of the Al-free composition. Such different elastic properties are due to the effect of lattice contraction as a whole and the specific chemical substitution mechanism that affect bonds strength. Al-bearing shy-B with lower velocity, higher anisotropy and wider thermodynamic stability can help to understand the low velocity zone and high anisotropy region in the subducted slab located in Tonga.
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