Elasticity of phase-Pi (Al3Si2O7(OH)3) – A hydrous aluminosilicate phase

Abstract

Phase-Pi (Al 3 Si 2 O 7 (OH) 3) is an aluminosilicate hydrous mineral and is likely to be stable in hydrated sedimentary layers of subducting slabs. Phase-Pi is likely to be stable between the depths of 60 and 200 km and is likely to transport water into the Earth's interior. Here, we use first principles simulations based on density functional theory to explore the crystal structure at high-pressure, equation of state, and full elastic stiffness tensor as a function of pressure. We find that the pressure volume results could be described by a finite strain fit with ! " , # " , and # " ′ being 310.3 Å 3 , 133 GPa, and 3.6 respectively. At zero pressure, the full elastic stiffness tensor shows significant anisotropy with the diagonal principal components % && , % '' , and % ((being 235, 292, 266 GPa respectively, the diagonal shear %)) , % ** , and % ++ being 86, 92, and 87 GPa 2 respectively, and the off-diagonal stiffness % &

Anomalous elastic behavior of phase Egg, AlSiO3(OH), at high pressures

“…Our pressure volume results and the evolution of lattice parameter upon compression are in good agreement with previous experiments (Vanpeteghem et al 2003). High-pressure symmetrization of hydrogen bond has been reported in many hydrous minerals including ice phases (Goncharov et al, 1996); δ-AlOOH (Tsuchiya et al, 2002;Panero and Stixrude, 2004;Tsuchiya and Tsuchiya, 2009;Sano-Furukawa et al, 2010;Mashino et al, 2016); δ-CrOOH analog to the δ-AlOOH phase (Jahn et al, 2012); ε-FeOOH (Otte et al, 2009); phase D (Tsuchiya et al, 2005;Hushur et al, 2011); phase H (Tsuchiya and Mookherjee, 2005;Panero and Caracas, 2017) and phase Pi (Peng et al, 2017). This is a preprint, the final version is subject to change, of the American Mineralogist (MSA) Cite as Authors (Year) Title.…”

“…However, for phase Egg we notice that the O(4)-H…O(3) angle to be around 160 o at pressures where proton transfer occurs (~ 15 GPa), leading to a new configuration of O(4)…H-O(3)(Figure 2). In a recently examined hydrous aluminosilicate phase Pi, similar observation was made, few of the O-H…O configurations remained non-linear even after compressions, however the O-H…O configuration that exhibited symmetric hydrogen bonding at high pressure became linear(Peng et al, 2017). In addition, a new monoclinic phase of AlOOH has been predicted which has nonlinear and bent O-H-O linkages instead of symmetric hydrogen bonding at high pressures(Zhong et al, 2016).…”

“…The observed trend in the density, and shear wave velocity could be explained in terms of the crystal structures. For instance, the crystal structure of phase-Pi, that is stable at relatively low pressures between 2 and 7 GPa (Wunder et al, 1993a,b), consists of layers of distorted eight-membered rings formed by AlO 6 units alternating with layers consisting of SiO 4 tetrahedral units (Peng et al, 2017). Crystal structure of topaz-OH, that is stable up to GPa (Ono, 1998), also consists of edge sharing AlO 6 octahedral units forming crankshaft chains and SiO 4 tetrahedral units sharing corners.…”

“…American Mineralogist, in press. DOI: https://doi.org/10.2138/am-2019-6694 pressure (loP) and high-pressure (hiP) phase Egg and other mineral phases including, stishovite (Karki et al, 1997) topaz-OH (Mookherjee et al, 2016), phase Pi (Peng et al, 2017), and δ-AlOOH (Tsuchiya and Tsuchiya, 2009) that are likely stable in subducted sediments. (c) A pressure-temperature-depth phase diagram illustrating the stability of phase Egg.…”

Intercalation of Water in Kaolinite (Al2Si2O5(OH)4) at Subduction Zone Conditions: Insights from Raman Spectroscopy

“…At higher pressures (∼6.1 GPa), the K-II phase eventually transforms to the K-III phase (Figure 5), and K-III eventually decomposes to phase-pi (Al 3 Si 2 O 7 (OH) 3 ) at ∼7 GPa. 21,69,70 This transformation is likely to be associated with the release of aqueous fluids and might contribute to dehydration-related seismicity. Similarly, at higher temperatures, the super-hydrated phase is also likely to dehydrate, which would release aqueous fluids and might induce subduction zone seismicity.…”