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Abstract Hydrated sulfates have been identified and studied in a wide variety of environments on Earth, Mars, and the icy satellites of the solar system. The subsurface presence of hydrous sulfur-bearing phases to any extent necessitates a better understanding of their thermodynamic and elastic properties at pressure. End-member experimental and computational data are lacking and are needed to accurately model hydrous, sulfur-bearing planetary interiors. In this work, high-pressure X-ray diffraction (XRD) and synchrotron Fourier-transform infrared (FTIR) measurements were conducted on szomolnokite (FeSO4·H2O) up to ~83 and 24 GPa, respectively. This study finds a monoclinic-triclinic (C2/c to P1) structural phase transition occurring in szomolnokite between 5.0(1) and 6.6(1) GPa and a previously unknown triclinic-monoclinic (P1 to P21) structural transition occurring between 12.7(3) and 16.8(3) GPa. The high-pressure transition was identified by the appearance of distinct reflections in the XRD patterns that cannot be attributed to a second phase related to the dissociation of the P1 phase, and it is further characterized by increased H2O bonding within the structure. We fit third-order Birch-Murnaghan equations of state for each of the three phases identified in our data and refit published data to compare the elastic parameters of szomolnokite, kieserite (MgSO4·H2O), and blödite (Na2Mg(SO4)2·4H2O). At ambient pressure, szomolnokite is less compressible than blödite and more than kieserite, but by 7 GPa both szomolnokite and kieserite have approximately the same bulk modulus, while blödite’s remains lower than both phases up to 20 GPa. These results indicate the stability of szomolnokite’s high-pressure monoclinic phase and the retention of water within the structure up to pressures found in planetary deep interiors. 

Walter et al . issue a number of critical comments on our report about the discovery of davemaoite to the end that they believe to show that our results do not provide compelling evidence for the presence of davemaoite in the type specimen and that the hosting diamond had formed in the lithosphere. Their claim is based on a misinterpretation of the diffraction data contained in the paper, an insufficient analysis of the compositional data that disregards the three-dimensional distribution of inclusions, and the arbitrary assumption that Earth’s mantle shows no lateral variations in temperature, inconsistent with state-of-the-art assessments of mantle temperature variations and with their own published results. 

Monolayer ternary tellurides based on alloying different transition metal dichalcogenides (TMDs) can result in new two‐dimensional (2D) materials ranging from semiconductors to metals and superconductors with tunable optical and electrical properties. Semiconducting WTe_2xS_2(1‐x)monolayer possesses two inequivalent valleys in the Brillouin zone, each valley coupling selectively with circularly polarized light (CPL). The degree of valley polarization (DVP) under the excitation of CPL represents the purity of valley polarized photoluminescence (PL), a critical parameter for opto‐valleytronic applications. Here, new strategies to efficiently tailor the valley‐polarized PL from semiconducting monolayer WTe_2xS_2(1‐x)at room temperature (RT) through alloying and back‐gating are presented. The DVP at RT is found to increase drastically from < 5% in WS₂to 40% in WTe_0.12S_1.88by Te‐alloying to enhance the spin‐orbit coupling. Further enhancement and control of the DVP from 40% up to 75% is demonstrated by electrostatically doping the monolayer WTe_0.12S_1.88via metallic 1T′‐WTe₂electrodes, where the use of 1T′‐WTe₂substantially lowers the Schottky barrier height (SBH) and weakens the Fermi‐level pinning of the electrical contacts. The demonstration of drastically enhanced DVP and electrical tunability in the valley‐polarized emission from 1T′‐WTe₂/WTe_0.12S_1.88heterostructures paves new pathways towards harnessing valley excitons in ultrathin valleytronic devices for RT applications.

 

Dense polymorphs of silica have been demonstrated experimentally to incorporate from 1.5 wt% to as much as 11.6 wt% H₂O as OH groups, with implications for the hydrogen budgets of Earth and other planets. This OH is thought to enter the SiO₂structure via a charge‐balanced substitution in which silicon vacancies (V_Si) are compensated by protonating four of the surrounding six oxygen atoms, often referred to as a hydrogarnet‐type defect. There are many possible configurations for this defect structure in dense silica, but the nature of these configurations and whether they can be distinguished experimentally is unknown. We present here density functional theory calculations that systematically assess the possible configurations of a hydrogarnet‐type defect in stishovite (rutile‐type SiO₂), with direct comparisons to experimental vibrational spectroscopy data. We predict that stishovite synthesized at 450 K and 10 GPa quenched to room temperature is dominated by a single defect type with tetrahedral geometry. This leads to OH stretching modes (2,500–3,000 cm⁻¹) and SiOH bending modes (∼1,400–1,450 cm⁻¹) largely consistent with experimentally observed modes. One remaining issue is that our calculations produce results compatible with experimental data on H to D exchange, but do not explain why a considerable fraction of the 1,420 cm⁻¹mode shifts by only 40 cm⁻¹in deuterated samples. At elevated pressures and temperatures, we find that a second square planar defect configuration also becomes favorable, leading to modes that should allow differentiation from the tetrahedral configuration.

 

Calcium silicate perovskite, CaSiO 3 , is arguably the most geochemically important phase in the lower mantle, because it concentrates elements that are incompatible in the upper mantle, including the heat-generating elements thorium and uranium, which have half-lives longer than the geologic history of Earth. We report CaSiO 3 -perovskite as an approved mineral (IMA2020-012a) with the name davemaoite. The natural specimen of davemaoite proves the existence of compositional heterogeneity within the lower mantle. Our observations indicate that davemaoite also hosts potassium in addition to uranium and thorium in its structure. Hence, the regional and global abundances of davemaoite influence the heat budget of the deep mantle, where the mineral is thermodynamically stable. 

Paqueite (Ca₃TiSi₂[Al,Ti,Si]₃O₁₄; IMA 2013‐053) and burnettite (CaVAlSiO₆; IMA 2013‐054) are new refractory minerals, occurring as euhedral to subhedral crystals within aluminous melilite in A‐WP1, a type A Ca‐Al‐rich inclusion, andCGft‐12, a compact type A (CTA) from the Allende CV3 carbonaceous chondrite. Type paqueite from A‐WP1 has an empirical formula of (Ca_2.91Na_0.11)Ti⁴⁺Si₂(Al_1.64Ti⁴⁺_0.90Si_0.24V³⁺_0.12Sc_0.07Mg_0.03)O₁₄, with a trigonal structure in space groupP321 and cell parametersa = 7.943 Å,c = 4.930 Å, V = 269.37 ų, andZ = 1. Paqueite’s general formula is Ca₃TiSi₂(Al,Ti,Si)₃O₁₄and the endmember formula is Ca₃TiSi₂(Al₂Ti)O₁₄. Type burnettite fromCGft‐12has an empirical formula of Ca_1.01(V³⁺_0.56Al_0.25Mg_0.18)(Si_1.19Al_0.81)O₆. It assumes a diopside‐typeC2/cstructure witha = 9.80 Å,b = 8.85 Å,c = 5.36 Å, β = 105.6°,V = 447.7 ų, andZ = 4. Burnettite’s general formula is Ca(V,Al,Mg)AlSiO₆and the endmember formula is CaVAlSiO₆. Paqueite and burnettite likely originated as condensates, but the observed grains may have crystallized from local V‐rich melts produced during a later thermal event. ForCGft‐12, the compositions of paqueite, clinopyroxene, and perovskite suggest that type As drew from two distinct populations of grains. Hibonite grains drew from multiple populations, but these were well mixed and not equilibrated prior to incorporation into type A host melilite.

 

In this paper, we discuss the occurrence of liebermannite (IMA2013‐128),KAlSi₃O₈, a new, shock‐generated, high‐pressure tetragonal hollandite‐type structure silicate mineral, in the Zagami basaltic shergottite meteorite. Liebermannite crystallizes in space groupI4/mwithZ = 2, cell dimensions ofa = 9.15 ± 0.14 (1σ) Å,c = 2.74 ± 0.13 Å, and a cell volume of 229 ± 19 Å³(for the type material), as revealed by synchrotron diffraction. In Zagami, liebermannite likely formed via solid‐state transformation of primary igneous K‐feldspar during an impact event that achieved pressures of ~20 GPa or more. The mineral name is in honor of Robert C. Liebermann, a high‐pressure mineral physicist at Stony Brook University, New York,USA.