We synthesized two C-S-H compounds from a mixture of carbon and sulfur in hydrogen-C : (H 2 S) 2 H 2 and from sulfur in mixed methane-hydrogen fluids-(CH 4 ) x (H 2 S) (2−x) H 2 at 4 GPa. X-ray synchrotron single-crystal diffraction and Raman spectroscopy have been applied to these samples up to 58 and 143 GPa, respectively. Both samples show a similar Al 2 Cu-type I4/mcm basic symmetry, while the hydrogen subsystem evolves with pressure via variously ordered molecular and extended modifications. The methane-bearing sample lowers symmetry to an orthorhombic Pnma structure after laser heating to 1400 K at 143 GPa. The results suggest that C-S-H compounds are structurally different from a common Im-3m H 3 S.

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The atomic and electronic structures of Cu 2 H and CuH have been investigated by high-pressure nuclear magnetic resonance spectroscopy up to 96 GPa, X-ray diffraction up to 160 GPa, and density functional theory-based calculations. Metallic Cu 2 H was synthesized at a pressure of 40 GPa, and semimetallic CuH at 90 GPa, found stable up to 160 GPa. For Cu 2 H, experiments and computations show an anomalous increase in the electronic density of state at the Fermi level for the hydrogen 1s states and the formation of a hydrogen network in the pressure range 43-58 GPa, together with high 1 H mobility of ∼10 −7 cm 2 /s. A comparison of these observations with results on FeH suggests that they could be common features in metal hydrides.

Subduction of oceanic lithosphere can bring water embedded within hydrous minerals into Earth's interior, which would affect physical and chemical properties, rheology, geodynamics, and thermo-chemical evolution of our planet (

Our knowledge of the structure and composition of Earth's core is based on sparse direct evidence (e.g., from seismology, geodesy, geo-and paleo-magnetism) and many indirect observations (from cosmochemistry, experimental petrology, and mineral physics) (Allègre et al., 1995;McDonough & Sun, 1995). Cosmochemical studies on iron meteorites and a comparison of mineral physics data with seismological observations (measurements of density (ρ) and compressional (V P ) and shear (V S ) wave velocities under extreme conditions) suggest that Earth's inner core is primarily composed of metallic Fe-Ni alloy (5-25 wt.% Ni) (McDonough & Sun, 1995;Wasson & Chou, 1974). However, the inner core density is ∼5 % lower than pure Fe at corresponding pressures and temperatures (Dewaele et al., 2006;Fei et al., 2016), presumably due to the presence of light elements (Birch, 1952) that were incorporated in the core during its formation (

Water transported by subducted oceanic plates changes mineral and rock properties at high pressures and temperatures, affecting the dynamics and evolution of the Earth’s interior. Although geochemical observations imply that water should be stored in the lower mantle, the limited amounts of water incorporation in pyrolitic lower-mantle minerals suggest that water in the lower mantle may be stored in the basaltic fragments of subducted slabs. Here, we performed multianvil experiments to investigate the stability and water solubility of aluminous stishovite and CaCl 2 -structured silica, referred to as poststishovite, in the SiO 2 -Al 2 O 3 -H 2 O systems at 24 to 28 GPa and 1,000 to 2,000 °C, representing the pressure–temperature conditions of cold subducting slabs to hot upwelling plumes in the top lower mantle. The results indicate that both alumina and water contents in these silica minerals increase with increasing temperature under hydrous conditions due to the strong Al 3+ -H + charge coupling substitution, resulting in the storage of water up to 1.1 wt %. The increase of water solubility in these hydrous aluminous silica phases at high temperatures is opposite of that of other nominally anhydrous minerals and of the stability of the hydrous minerals. This feature prevents the releasing of water from the subducting slabs and enhances the transport water into the deep lower mantle, allowing significant amounts of water storage in the high-temperature lower mantle and circulating water between the upper mantle and the lower mantle through subduction and plume upwelling. The shallower depths of midmantle seismic scatterers than expected from the pure SiO 2 stishovite–poststishovite transition pressure support this scenario.

While it is accepted that the lower mantle phase assemblage is comprised primarily of Al-and Fe-bearing MgSiO 3 bridgmanite, the exact proportion and the bulk composition of the lower mantle as a whole remain uncertain. The abundance of bridgmanite relative to ferropericlase will be controlled by the bulk Mg/Si ratio. In a pyrolite composition, which is believed to represent the average composition of the upper mantle (Ringwood, 1962), this ratio is ∼1.3 and a pyrolytic lower mantle assemblage would be comprised of ∼78% bridgmanite, 15% ferropericlase, and 7% calcium perovskite by volume (e.g., Irifune, 1994;Irifune et al., 2010;Ishii et al., 2011). The Earth is frequently proposed to have formed from carbonaceous chondrites, however, which have a Mg/Si ratio much closer to 1.0 (Palme & O'Neill, 2004). Aside from Si potentially entering the Earth's core (e.g., Poirier, 1994;Wänke, 1981), one way to explain the Mg/Si ratio of the upper mantle is if the lower mantle is richer in bridgmanite as a result of fractional crystallization during the magma ocean stage of Earth's history (e.g., Ballmer et al., 2017;Elkins-Tanton, 2012;Tonks & Melosh, 1993). This scenario is supported by shear wave velocity measurements of MgSiO 3 and Al-bearing bridgmanite at pressures over 1 Mbar (Murakami et al., 2012), for which comparison with the PREM seismic velocity model indicates a lower mantle containing at least 93 vol% of bridgmanite.In the previous studies of Murakami et al. (2007Murakami et al. ( , 2012, performed in the DAC using Brillouin scattering measurements, it was not possible to directly measure values of v P , which were instead estimated using bulk modulus determinations from previous static compression measurements (Fiquet et al., 2000). This potential cause of uncertainty arises in high pressure Brillouin scattering measurements because the v P signal overlaps with the much more intense v S signal of the diamond anvils. This effect is particularly pronounced for polycrystalline samples (Murakami et al., 2007(Murakami et al., , 2012, where the sample peaks are broad and tend to overlap with diamond even at ambient pressure. To overcome this problem, Fu et al. (2019) combined Brillouin scattering measurements of v S with impulsive stimulated light scattering (ISLS) measurements for v P to examine bridgmanite single crystals at 25 and 35 GPa, because ISLS has the advantage that the signal originating from the sample does not overlap with that of the diamond anvils. Fu et al. (2019) studied two bridgmanite samples with different Fe and Al contents. The determined bridgmanite elastic anisotropy

Akimotoite, a MgSiO3 polymorph, present in the lower transition zone within ultramafic portions of subducting slabs and potentially also in the ambient mantle, will partition some amount of Al, raising the question of how this will affect its crystal structure and properties. In this study, a series of samples along the MgSiO3 akimotoite -Al2O3 corundum solid solution have been investigated by means of single-crystal X-ray diffraction in order to examine their crystal chemistry. Results show a strong non-linear behavior of the aand c-axes as a function of Al content, which arises from fundamentally different accommodation mechanisms in the akimotoite and corundum structures. Furthermore, two Al2O3-bearing akimotoite samples were investigated at high pressure in order to determine the different compression mechanisms associated with Al substitution. Al2O3-bearing akimotoite becomes more compressible at least up to a content of 20 mol% Al2O3, due likely to an increase in compressibility as the Al cation is incorporated into the SiO6 octahedron. This observation is in strong contrast to the stiffer corundum end-member having a KT = 250 GPa larger than that of the akimotoite end-member (KT = 205(1) GPa). These findings have implications for mineral physics models of elastic properties, which have in the past assumed linear mixing behavior between the MgSiO3 akimotoite and Al2O3 corundum end-members in order to calculate sound wave velocities for Al-bearing akimotoite at high pressure and temperature.