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@ARTICLE{Li:465687,
author = {Li, Xinyang and Speziale, Sergio and Glazyrin, Konstantin
and Wilke, Franziska D. H. and Liermann, Hanns-Peter and
Koch-Mueller, Monika},
title = {{S}ynthesis, structure refinement and single-crystal
elasticity of {A}l-bearing superhydrous phase {B}},
journal = {American mineralogist},
volume = {107},
number = {5},
issn = {0003-004X},
address = {Alexandria, Va.},
publisher = {GeoScienceWorld},
reportid = {PUBDB-2021-03999},
pages = {885 - 895},
year = {2021},
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.},
cin = {FS-PETRA-D},
ddc = {540},
cid = {I:(DE-H253)FS-PETRA-D-20210408},
pnm = {631 - Matter – Dynamics, Mechanisms and Control
(POF4-631) / 6G3 - PETRA III (DESY) (POF4-6G3)},
pid = {G:(DE-HGF)POF4-631 / G:(DE-HGF)POF4-6G3},
experiment = {EXP:(DE-H253)P-P02.2-20150101},
typ = {PUB:(DE-HGF)16},
UT = {WOS:000790666400010},
doi = {10.2138/am-2022-7989},
url = {https://bib-pubdb1.desy.de/record/465687},
}