The partitioning of light elements between liquid and solid at the inner core boundary (ICB) governs compositional difference and density deficit between the outer and inner core. Observations of high S and low Fe concentration on the surface of Mercury from MESSENGER mission indicate that Mercury is formed under much more reduced conditions than other terrestrial planets, which may result in a Si and S-bearing metallic Fe core. In this study, we conducted high-pressure experiments to investigate the partitioning behavior of Si and S between liquid and solid in the Fe-Si-S system at 15 and 21GPa, relevant to Mercury's ICB conditions. Experimental results show that almost all S partitions into liquid. The partitioning coefficient of Si (D-Si) between liquid and solid is strongly correlated with the S content in liquid (X-S(liquid)) as: log(10)(D-Si) = 0.0445 + 5.9895 * log(10)(1 - X-S(liquid)). Within our experimental range, pressure has limited effect on the partitioning behavior of Si and S between liquid and solid. For Mercury with an Fe-Si- S core, compositional difference between the inner and outer core is strongly dependent on the S content of the core. The lower S content is in the core, the smaller compositional difference and density deficit between the liquid outer core and solid inner core should be observed. For a core with 1.5wt% bulkS, amodel ICB temperature would intersect with the melting curve at similar to 17GPa, corresponding to an inner core with a radius of similar to 1600km. (C) 2021 Elsevier B.V. All rights reserved.

We investigate energetically favorable structures of ABO(2)N oxynitrides as functions of pressure and strain via swarm-intelligence-based structure prediction methods, density functional theory (DFT) lattice dynamics and first-principles molecular dynamics. We predict several thermodynamically stable polar oxynitride perovskites under high pressures. In addition, we find that ferroelectric polar phases of perovskite-structured oxynitrides can be thermodynamically stable and synthesized at high pressure on appropriate substrates. The dynamical stability of the ferroelectric oxynitrides under epitaxial strain at ambient pressure also implies the possibility to synthesize them using pulsed laser deposition or other atomic layer deposition methods. Our results have broad implications for further exploration of other oxynitride materials as well. We performed first-principles molecular dynamics and find that the polar perovskite of YSiO2N (I4cm) is metastable up to at least 600 K under compressive epitaxial strain before converting to the stable wollastonitelike structures (I4/mcm). We predict that YGeO2N, LaSiO2N, and LaGeO2N are metastable as ferroelectric perovskites (P4mm) at zero pressure even without epitaxial strain.

We study the high-pressure structures of SrB6 up to 200 GPa using first-principles structure prediction calculations and high-pressure x-ray diffraction experiments. The computations show that the ambient-pressure cubic phase transforms to an orthorhombic structure (Cmmm) at 48 GPa, and then to a tetragonal structure (14/mmm) at 60 GPa. The high-pressure experiments are consistent with the theoretically predicted tetragonal structure, which was quenched successfully to ambient conditions. Pressure induces simple boron octahedra to form complex networks in which the electrons are delocalized, leading to metallic ground states with large density of states at the Fermi level. Calculated stress-strain relations for the 14/mmm structure of SrB6 demonstrate its intrinsic hard nature with an estimated Vickers hardness of 15 GPa, and reveal a novel deformation mechanism with transient multicenter bonding that results in the combination of high strength and high ductility. Our findings offer valuable insights for understanding the rich and complex crystal structures of SrB6, which have broad implications for further explorations of hexaboride materials.

The onset of modern plate tectonic regime on Earth became increasingly controversial in recent years because of the lack of continuously newly found records of subduction and collision. Here, we present the study of the ultra-high pressure eclogite xenoliths in the Paleoproterozoic Fengzhen carbonatite complex, including the garnet-rich (Fz-2) and the omphacite-rich (Fz-16) samples. All samples are collected from the same site and exhibit identical mineral chemistry and textures. The xenoliths display whole-rock compositions indicative of the protoliths of oceanic gabbro. At least two metamorphic stages are recognized in these eclogites epidote/amphibole-eclogite stage M1 and lawsonite-eclogite stage M2. Coesite pseudomorph within radial cracks occurs as inclusions in garnet and omphacite. Columnar lawsonite pseudomorph as aggregates of coexisted kyanite and zoisite occasionally present as inclusion in garnet. The porphyroblastic garnet exhibits an inclusion-rich core and an inclusion-poor rim. The garnet displays compositional zoning, with the increasing pyrope and decreasing almandine content from core to rim. The phase equilibria modeling records the prograde path from amphibole-eclogite phase to lawsonite eclogite phase, at pressure and temperature of 2.6 similar to 3.7GPa and 655 similar to 670 degrees C, recorded from garnet zonation. The garnet-omphacite-phengite-kyanite-quartz thermobarometry yields a pressure and temperature of 3.0GPa and 734 degrees C. The Zr-in-rutile thermometer also gives a similar temperature range of 601 similar to 685 degrees C at 2.6 similar to 3.7GPa. The coesite and lawsonite pseudomorphs within the garnet and omphacite support the existence of the lawsonite-eclogite stage, representing the oldest record of low temperature ultra-high pressure metamorphic rock in the world. With a thermal gradient of 216 +/- 35 degrees C/GPa, the eclogite rocks supports the onset of modern-style cold subduction prior to similar to 1.8Ga.

A glassy carbon phosphonitride material with bulk chemical composition roughly approximating C3N3P was synthesized through a high-pressure, high-temperature process using a pure P(CN)(3) molecular precursor. The resulting material (hereafter referred to as "HPHT-C3N3P") was characterized using a variety of techniques, including X-ray scattering, pair distribution function analysis, P-31, C-13,N-15 magic-angle spinning nuclear magnetic resonance spectroscopies; X-ray photoelectron spectroscopy, and Raman and IR spectroscopies. The measurements indicate that HPHT-C3N3 P lacks long-range structural order with a local structure predominantly composed of a sp(2) , s-triazine-like network in which phosphorus atoms substitute for bridging nitrogen sites found in related C3N4 materials. The HPHT-C3N3P sample exhibits semiconducting properties, with electrical transport dominated by variable-range hopping. The high phosphorus content of HPHT-C3N3P (approaching 13 at. %) is associated with a major decrease in the optical absorption edge (similar to 0.4 eV) and a similar to 10(10)-fold increase in electrical conductivity, as compared to previously-reported P-doped graphitic g-C3N4 (0.6-3.8 at. % P). The HPHT-C3N3P sample is considerably harder than layered g-C3N4 and exhibits superior thermal stability up to , similar to 700 degrees C in air. These results demonstrate a remarkable range of tunable properties possible for C3N4-related materials through elemental substitution and provide valuable information to guide the design of new materials.

Whether modern-style subduction exists in Paleoproterozoic has been hotly debated because of the scarcity of robust petrological evidence. Here, we present a comprehensive study of olivine-bearing garnet pyroxenite xenoliths hosted in the Paleoproterozoic Fengzhen carbonatite. The carbonatite is located in the conjugate area between the Paleoproterozoic Trans-North China Orogen (TNCO) and the Khondalite Belt in North China Craton (NCC) with a dated age of 1810 +/- 3 Ma. Petrographically, four-stages of evolution have been identified in the studied olivine-bearing garnet pyroxenite: 1) the formation of the protolith spinel websterite (S1), 2) the prograde metamorphism of spinel-lherzolite facies to garnet-lherzolite facies (M1), 3) retrograde metamorphism to Ariegite subfacies (M2) with formation of symplectite-I, and 4) Seiland subfacies (M3) forming symplectite-II. The clinopyroxene in the xenoliths display high Mg# (Mg2+/(Mg2++Fe2+)*100 = 89-94), strongly depleted HREE (heavy REE) and HFSE (high field strength elements; e.g., Nb, Zr, Ti) and enriched LREE (light REE) and LILE (large ion lithophile elements; e.g., Th and U). Similarly, the whole-rock chemistry exhibits high Mg# (85-88) and high Al2O3 + CaO (20.2-21.9 wt%) with enrichment in LREE and LILE (Th, U) and depletion in HREE and HFSE (e.g., Nb, Ta, Zr, Hf, Ti). The geochemical signatures imply that they might originate from the refractory mantle wedge in subduction zone and have been metasomatized by crust-derived melts. Major mineral thermobarometry yields the peak PT conditions of 26-33 kbar and 890-962 degrees C corresponding to a cold subduction geothermal gradient (307 +/- 35 degrees C/GPa) with a depth up to 110 km for olivine-bearing garnet pyroxenites, which is also consistent with the results by zirconium-in-rutile and REE thermobarometers. This studies suggest that that the modern-style subduction of the lithospheric mantle was initiated at least since 1.8 Ga.

Raman spectroscopic measurements of the arsenolite-hydrogen inclusion compound As4O6.2H(2) were performed in diamond anvil cells at high pressure and variable temperature down to 80 K. The experimental results were complemented by ab initio molecular dynamics simulations and phonon calculations. Observation of three hydrogen vibrons in As4O6.2H(2) is reported in the entire temperature and pressure range studied (up to 24 GPa). While the experiments performed with protium and deuterium at variable temperatures allowed for the assignment of two vibrons as Q(1)(1) and Q(1)(0) transitions of ortho and para spin isomers of hydrogen trapped in the inclusion compound, the origin of the third vibron could not be unequivocally established. Low-temperature spectra revealed that the lowest-frequency vibron is actually composed of two overlapping bands of A(g) and T-2g symmetries dominated by H-2 stretching modes as predicted by our previous density functional theory calculations. We observed low-frequency modes of As4O6.2H(2) vibrations dominated by H-2 "librations," which were missed in a previous study. A low-temperature fine structure was observed for the J = 0 -> 2 and J = 1 -> 3 manifolds of hydrogen trapped in As4O6.2H(2), indicating the lifting of degeneracy due to an anisotropic environment. A non-spherical distribution was captured by molecular dynamics simulations, which revealed that the trajectory of H-2 molecules is skewed along the crystallographic 111 direction. Last but not least, low-temperature synchrotron powder x-ray diffraction measurements on As4O6.2H(2) revealed that the bulk structure of the compound is preserved down to 5 K at 1.6 GPa.

Observations of high ferric iron content in diamond garnet inclusions and mantle plume melts suggest a highly heterogeneous distribution of ferric iron in the mantle. Recycling of oxidized materials such as carbonates from Earth's surface by subduction could explain the observed variations. Here we present high-pressure high-temperature multi-anvil experiments to determine the redox reactions between calcium-, magnesium-, or iron-carbonate and ferrous iron-bearing silicate mineral (garnet or fayalite) at conditions representative of subduction zones with intermediate thermal structures. We show that both garnet and fayalite can be oxidized to ferric iron-rich garnets accompanied by reduction of calcium carbonate to form graphite. The ferric iron content in the synthetic garnets increases with increasing pressure, and is correlated with the Ca content in the garnets. We suggest that recycled sedimentary calcium carbonate could influence the evolution of the mantle oxidation state by efficiently increasing the ferric iron content in the deep upper mantle. Calcium carbonate transported by subducting slabs could explain elevated ferric iron content in the upper mantle through redox reactions with iron-rich garnet and graphite as products, according to high-pressure, high-temperature experiments