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Nature chemistry 15(5), 641 - 646 (2023). doi:10.1038/s41557-023-01148-7, The recent high-pressure synthesis of pentazolates and the subsequent stabilization of the aromatic $[N_5]^−$ anion at atmospheric pressure have had an immense impact on nitrogen chemistry. Other aromatic nitrogen species have also been actively sought, including the hexaazabenzene $N_6 $ring. Although a variety of configurations and geometries have been proposed based on ab initio calculations, one that stands out as a likely candidate is the aromatic hexazine anion $[N_6]^{4−}$. Here we present the synthesis of this species, realized in the high-pressure potassium nitrogen compound $K_9N_{56}$ formed at high pressures (46 and 61 GPa) and high temperature (estimated to be above 2,000 K) by direct reaction between nitrogen and $KN_3$ in a laser-heated diamond anvil cell. The complex structure of $K_9N_{56}$—composed of 520 atoms per unit cell—was solved based on synchrotron single-crystal X-ray diffraction and corroborated by density functional theory calculations. The observed hexazine anion $[N_6]^{4−}$ is planar and proposed to be aromatic., Published by Nature Publishing Group, London

The internal structure of Mercury holds key information regarding the planet’s formation and its peculiar magnetic field. Waiting for incoming observations by BepiColombo, current knowledge of the interior structure of Mercury relies primarily on geodetic and surface chemistry data collected by MESSENGER. Results from spectral and compositional analysis supplemented by cosmochemical evidence indicate that light elements such as S, and Si are most likely alloyed to Fe in Mercury’s core. This notion is further supported by the very reducing redox conditions (from -2.6 to -7.3 log units below Fe-FeO oxygen buffer) predicted to occur during the planet’s differentiation that argue for significant quantities of Si and S partitioned into metallic iron. Thus, it is of primary importance to determine the Fe-Si-S phase diagram and to understand the high pressure and high temperature properties and thermodynamic behavior of Fe-Si-S alloys at conditions directly relevant for Mercury’s core. Very recently the binary Fe-FeSi phase diagram has been established at Mercury’s core conditions, but phase and melting relations in the Fe-Si-S ternary system still are poorly constrained, in particular at the relatively low pressures and temperatures relevant for Mercury’s core.To address this issue, we performed angular dispersive powder X-ray diffraction experiments in laser-heated diamond anvil cells on selected composition in the Fe-Si-S system (i.e., Fe-4S-6Si, Fe-16S-6Si, Fe-4S-12Si, and Fe-16S-12Si, all in wt. %) at the P02.2 Extreme Conditions beamline at DESY Synchrotron facility (Germany). For all compositions, eutectic melting and subsolidus phase relations were investigated up to about 45 GPa. Ex situ chemical analysis of the recovered run products were performed at the IMPMC laboratory on the extracted FIB thin sections cut throughout the heated spots.Here we will present preliminary results on the eutectic melting and Fe-Si-S phase relations as a function of pressure, temperature and composition, with specific focus to the conditions expected within the core of Mercury.

We show, by single-crystal diffraction studies in laser-heated diamond-anvil cells, that Ca2CO4 orthocarbonate, which contains CO44− tetrahedra, can be formed already at ~20 GPa at ~1830 K, i.e., at much lower pressures than other carbonates with sp3-hybridized carbon. Ca2CO4 can also be formed at ~89 GPa and ~2500 K. This very broad P-T range suggests the possible existence of Ca2CO4 in the Earth’s transition zone and in most of the lower mantle. Raman spectroscopy shows the typical bands associated with tetrahedral CO44−-groups. DFT-theory based calculations reproduce the experimental Raman spectra and indicate that at least in the athermal limit the phase assemblage of Ca2CO4 + 2SiO2 is more stable than 2CaSiO3 + CO2 at high pressures.

Magnetite, Fe

High-pressure nitrogen chemistry has expanded at a formidable rate over the past decade, unveiling the chemical richness of nitrogen. Here, the Zn-N system is investigated in laser-heated diamond anvil cells by synchrotron powder and single-crystal X-ray diffraction, revealing three hitherto unobserved nitrogen compounds: β-Zn3N2, α-ZnN4, and β-ZnN4, formed at 35.0, 63.5, and 81.7 GPa, respectively. Whereas β-Zn3N2 contains the N3- nitride, both ZnN4 solids are found to be composed of polyacetylene-like [N4]∞2- chains. Upon the decompression of β-ZnN4 below 72.7 GPa, a first-order displacive phase transition is observed from β-ZnN4 to α-ZnN4. The α-ZnN4 phase is detected down to 11.0 GPa, at lower pressures decomposing into the known α-Zn3N2 (space group Ia3) and N2. The equations of states of β-ZnN4 and α-ZnN4 are also determined, and their bulk moduli are found to be K0 = 126(9) GPa and K0 = 76(12) GPa, respectively. Density functional theory calculations were also performed and provide further insight into the Zn-N system. Moreover, comparing the Mg-N and Zn-N systems underlines the importance of minute chemical differences between metal cations in the resulting synthesized phases.

We synthesized single crystals of marokite (CaMn2O4)-type orthorhombic manganese (II,III) oxide, γ-Mn3O4, in a multianvil apparatus at pressures of 10-24 GPa. The magnetic, electronic, and optical properties of the crystals were investigated at ambient pressure. It was found that γ-Mn3O4 is a semiconductor with an indirect band gap Eg of 0.96 eV and two antiferromagnetic transitions (TN) at ∼200 and ∼55 K. The phase stability of the γ-Mn3O4 crystals was examined in the pressure range of 0-60 GPa using single-crystal X-ray diffraction and Raman spectroscopy. A bulk modulus of γ-Mn3O4 was determined to be B0 = 235.3(2) GPa with B' = 2.6(6). The γ-Mn3O4 phase persisted over the whole pressure range studied and did not transform or decompose upon laser heating of the sample to ∼3500 K at 60 GPa. This result seems surprising, given the high-pressure structural diversity of iron oxides with similar stoichiometries. With an increase in pressure, the degree of distortion of MnO6 polyhedra decreased. Furthermore, there are signs indicating a limited charge transfer between the Mn3+ ions in the octahedra and the Mn2+ ions in the trigonal prisms. Our results demonstrate that the high-pressure behavior of the structural, electronic, and chemical properties of manganese oxides strongly differs from that of iron oxides with similar stoichiometries.

A gasket is an important constituent of a diamond anvil cell (DAC) assembly, responsible for the sample chamber stability at extreme conditions for X-ray diffraction studies. In this work, we studied the performance of gaskets made of metallic glass Fe

Two novel yttrium nitrides, YN

Carbonates containing CO4 groups as building blocks have recently been discovered. A new orthocarbonate, Sr2CO4 is synthesized at 92 GPa and at a temperature of 2500 K. Its crystal structure was determined by in situ synchrotron single‐crystal X‐ray diffraction, selecting a grain from a polycrystalline sample. Strontium orthocarbonate crystallizes in the orthorhombic crystal system (space group Pnma) with CO4, SrO9 and SrO11 polyhedra as the main building blocks. It is isostructural to Ca2CO4. DFT calculations reproduce the experimental findings very well and have, therefore, been used to predict the equation of state, Raman and IR spectra, and to assist in the discussion of bonding in this compound., A new orthocarbonate, Sr2CO4, was synthesized under extreme pressure and temperature conditions of 92 GPa and 2500 K, respectively. The crystal structure of the compound s fully characterized in situ by synchrotron single‐crystal X‐ray diffraction and DFT calculations were employed to provide insight into its equation of state, Raman and IR spectra, and bonding. image

The high-pressure behavior of simple molecular systems, devoid of strong intermolecular interactions, provides a unique avenue toward a fundamental understanding of matter. Tetrahalides of the carbon group elements (group 14), lacking all intermolecular interactions but van der Waals, are among the most elementary of molecular compounds. Here, we report the investigation of CF

Nature 605(7909), 274 - 278 (2022). doi:10.1038/s41586-022-04550-2, Theoretical modelling predicts very unusual structures and properties of materials at extreme pressure and temperature conditions1,2. Hitherto, their synthesis and investigation above 200 gigapascals have been hindered both by the technical complexity of ultrahigh-pressure experiments and by the absence of relevant in situ methods of materials analysis. Here we report on a methodology developed to enable experiments at static compression in the terapascal regime with laser heating. We apply this method to realize pressures of about 600 and 900 gigapascals in a laser-heated double-stage diamond anvil cell3, producing a rhenium–nitrogen alloy and achieving the synthesis of rhenium nitride Re$_7$N$_3$—which, as our theoretical analysis shows, is only stable under extreme compression. Full chemical and structural characterization of the materials, realized using synchrotron single-crystal X-ray diffraction on microcrystals in situ, demonstrates the capabilities of the methodology to extend high-pressure crystallography to the terapascal regime., Published by Nature Publ. Group, London [u.a.]

Review of scientific instruments 93(3), 033904 (2022). doi:10.1063/5.0071786, The success of high-pressure research relies on the inventive design of pressure-generating instruments and materials used for their construction. In this study, the anvils of conical frustum or disk shapes with flat or modified culet profiles (toroidal or beveled) were prepared by milling an Ia-type diamond plate made of a (100)-oriented single crystal using the focused ion beam. Raman spectroscopy and synchrotron x-ray diffraction were applied to evaluate the efficiency of the anvils for pressure multiplication in different modes of operation: as single indenters forced against the primary anvil in diamond anvil cells (DACs) or as pairs of anvils forced together in double-stage DACs (dsDACs). All types of secondary anvils performed well up to about 250 GPa. The pressure multiplication factor of single indenters appeared to be insignificantly dependent on the shape of the anvils and their culets’ profiles. The enhanced pressure multiplication factor found for pairs of toroidally shaped secondary anvils makes this design very promising for ultrahigh-pressure experiments in dsDACs., Published by American Institute of Physics, [S.l.]

Tungsten tetraboride has been known so far as a non-stoichiometric compound with a variable composition (e.g. WB$_{4−x}$, WB$_{4+x}$). Its mechanical properties could exceed those of hard tungsten carbide, which is widely used nowadays in science and technology. The existence of stoichiometric WB$_4$ has not been proven yet, and its structure and crystal chemistry remain debatable to date. Here we report the synthesis of single crystals of the stoichiometric WB$_4$ phase under high-pressure high-temperature conditions. The crystal structure of WB$_4$ was determined using synchrotron single-crystal X-ray diffraction. In situ high-pressure compressibility measurements show that the bulk modulus of WB$_4$ is 238.6(2) GPa for B′ = 5.6(0). Measurements of mechanical properties of bulk polycrystalline sub-millimeter size samples under ambient conditions reveal a hardness of ∼36 GPa, confirming that the material falls in the category of superhard materials.

Polynitrides are intrinsically thermodynamically unstable at ambient conditions and require peculiar synthetic approaches. Now, a one-step synthesis of metal-inorganic frameworks Hf4N20 center dot ...

Acta crystallographica / Section E 76(5), 715 - 719 (2020). doi:10.1107/S2056989020005411, The crystal structure of MgCO$_3$-II has long been discussed in the literature where DFT-based model calculations predict a pressure-induced transition of the carbon atom from the sp$^2$ to the sp$^3$ type of bonding. We have now determined the crystal structure of iron-bearing MgCO$_3$-II based on single-crystal X-ray diffraction measurements using synchrotron radiation. We laser-heated a synthetic (Mg$_{0.85}$Fe$_{0.15}$)CO$_3$ single crystal at 2500 K and 98 GPa and observed the formation of a monoclinic phase with composition (Mg$_{2.53}$Fe$_{0.47}$)C$_3$O$_9$ in the space group C2/m that contains tetra­hedrally coordinated carbon, where CO$_4$$^{4-}$ tetra­hedra are linked by corner-sharing oxygen atoms to form three-membered C$_3$O$_3$$^{6-}$ ring anions. The crystal structure of (Mg$_{0.85}$Fe$_{0.15}$)CO$_3$ (magnesium iron carbonate) at 98 GPa and 300 K is reported here as well. In comparison with previous structure-prediction calculations and powder X-ray diffraction data, our structural data provide reliable information from experiments regarding atomic positions, bond lengths, and bond angles., Published by National Center for Biotechnology Information, U.S. National Library of Medicine15046, Bethesda, MD

Changes in the bonding of carbon under high pressure leads to unusual crystal chemistry and can dramatically alter the properties of transition metal carbides. In this work, the new orthorhombic polymorph of yttrium carbide, $\ensuremath{\gamma}\text{\ensuremath{-}}{\mathrm{Y}}_{4}{\mathrm{C}}_{5}$, was synthesized from yttrium and paraffin oil in a laser-heated diamond anvil cell at $\ensuremath{\sim}50\text{ }\text{ }\mathrm{GPa}$. The structure of $\ensuremath{\gamma}\text{\ensuremath{-}}{\mathrm{Y}}_{4}{\mathrm{C}}_{5}$ was solved and refined using in situ synchrotron single-crystal x-ray diffraction. It includes two carbon groups: [${\mathrm{C}}_{2}$] dimers and nonlinear [${\mathrm{C}}_{3}$] trimers. Crystal chemical analysis and density functional theory calculations revealed unusually high noninteger charges (${[{\mathrm{C}}_{2}]}^{5.2\ensuremath{-}}$ and ${[{\mathrm{C}}_{3}]}^{6.8\ensuremath{-}}$) and unique bond orders ($l1.5$). Our results extend the list of possible carbon states at extreme conditions.

High-pressure nitrogen chemistry has expanded at a formidable rate over the past decade, unveiling the chemical richness of nitrogen. Here, the Zn-N system is investigated in laser-heated diamond anvil cells by synchrotron powder and single-crystal X-ray diffraction, revealing three hitherto unobserved nitrogen compounds: β-Zn

We synthesized single crystals of marokite (CaMn

Ferropericlase (Mg,Fe)O is the second most abundant mineral in Earth's lower mantle and a common inclusion found in subcratonic diamonds. Pyrolitic mantle has Mg# (100 × Mg/(Mg+Fe)) ~89. However, ferropericlase inclusions in diamonds show a broad range of Mg# between 12 and 93. Here we use Synchrotron Mössbauer Source (SMS) spectroscopy and single-crystal X-ray diffraction to determine the iron oxidation state and structure of two magnesiowüstite and three ferropericlase inclusions in diamonds from São Luiz, Brazil. Inclusion Mg#s vary between 16.1 and 84.5. Ferropericlase inclusions contain no ferric iron within the detection limit of SMS, while both magnesiowüstite inclusions show the presence of monocrystalline magnesioferrite ((Mg,Fe)Fe

Here, we present a method to study the equation of state of opaque amorphous and crystalline materials in diamond anvil cells. The approach is based on measurements of sample dimensions using high-resolution optical microscopy. Data on the volumetric strain as a function of pressure allow deriving the isothermal equation of state of the studied material. The analysis of optical images is fully automatized and allows measuring the sample dimensions with the precision of about 60 nm. The methodology was validated by studying isothermal compression of ω-Ti up to 30 GPa in a Ne pressure transmitting medium. Within the accuracy of the measurements, the bulk modulus of ω-Ti determined using optical microscopy was similar to that obtained from x-ray diffraction. For glassy carbon compressed to ∼30 GPa, the previously unknown bulk modulus was found to be equal to K0 = 28 (2) GPa [K′ = 5.5(5)].

High-pressure chemistry is known to inspire the creation of unexpected new classes of compounds with exceptional properties. Here, we employ the laser-heated diamond anvil cell technique for synthesis of a Dirac material BeN_{4}. A triclinic phase of beryllium tetranitride tr-BeN_{4} was synthesized from elements at ∼85 GPa. Upon decompression to ambient conditions, it transforms into a compound with atomic-thick BeN_{4} layers interconnected via weak van der Waals bonds and consisting of polyacetylene-like nitrogen chains with conjugated π systems and Be atoms in square-planar coordination. Theoretical calculations for a single BeN_{4} layer show that its electronic lattice is described by a slightly distorted honeycomb structure reminiscent of the graphene lattice and the presence of Dirac points in the electronic band structure at the Fermi level. The BeN_{4} layer, i.e., beryllonitrene, represents a qualitatively new class of 2D materials that can be built of a metal atom and polymeric nitrogen chains and host anisotropic Dirac fermions.

Extreme pressures and temperatures are known to drastically affect the chemistry of iron oxides, resulting in numerous compounds forming homologous series nFeOmFe2O3 and the appearance of FeO2. Here, based on the results of in situ single-crystal x-ray diffraction, Mössbauer spectroscopy, x-ray absorption spectroscopy, and density-functional theory+dynamical mean-field theory calculations, we demonstrate that iron in high-pressure cubic FeO2 and isostructural FeO2H0.5 is ferric (Fe3+), and oxygen has a formal valence less than 2. Reduction of oxygen valence from 2, common for oxides, down to 1.5 can be explained by a formation of a localized hole at oxygen sites. © 2021 American Physical Society. We acknowledge the Deutsches Elektronen-Synchrotron (DESY, PETRA III), the European Synchrotron Radiation Facility (ESRF), and the Advance Photon Source (APS) for provision of beamtime. N. D. and L. D. thank the Federal Ministry of Education and Research, Germany (BMBF, Grant No. 05K19WC1) and the Deutsche Forschungsgemeinschaft (DFG Projects No. DU 954–11/1, No. DU 393–9/2, and No. DU 393–13/1) for financial support. N. D. and I. A. A. thank the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University (Faculty Grant SFO-Mat-LiU No. 2009 00971). Electronic structure calculations were supported by the Russian Science Foundation (Project No. 18-12-00492). Theoretical analysis of chemical bonding was supported by the Ministry of Science and Higher Education of the Russian Federation in the framework of Increase Competitiveness Program of NUST “MISIS” (No. K2-2019-001) implemented by a governmental decree, No. 211. Support from the Knut and Alice Wallenberg Foundation (Wallenberg Scholar Grant No. KAW-2018.0194), the Swedish Government Strategic Research Areas and SeRC, and the Swedish Research Council (VR) Grant No. 2019-05600 is gratefully acknowledged.

Minerals 11(5), 516 (2021). doi:10.3390/min11050516, We report the high-pressure synthesis and the equation of state (EOS) of a novel nickel carbide (Ni$_3$C). It was synthesized in a diamond anvil cell at 184(5) GPa through a direct reaction of a nickel powder with carbon from the diamond anvils upon heating at 3500 (200) K. Ni$_3$C has the cementite-type structure (Pnma space group, a = 4.519(2) Å, b = 5.801(2) Å, c = 4.009(3) Å), which was solved and refined based on in-situ synchrotron single-crystal X-ray diffraction. The pressure-volume data of Ni$_3$C was obtained on decompression at room temperature and fitted to the 3rd order Burch-Murnaghan equation of state with the following parameters: V$_0$ = 147.7(8) Å$^3$, K$_0$ = 157(10) GPa, and K$_0$ ' = 7.8(6). Our results contribute to the understanding of the phase composition and properties of Earth's outer core., Published by MDPI, Basel

Physical review letters 124(21), 216001 (2020). doi:10.1103/PhysRevLett.124.216001, Studies of polynitrogen phases are of great interest for fundamental science and for the design of novel high energy density materials. Laser heating of pure nitrogen at 140 GPa in a diamond anvil cell led to the synthesis of a polymeric nitrogen allotrope with the black phosphorus structure, bp-N. The structure was identified in situ using synchrotron single-crystal x-ray diffraction and further studied by Raman spectroscopy and density functional theory calculations. The discovery of bp-N brings nitrogen in line with heavier pnictogen elements, resolves incongruities regarding polymeric nitrogen phases and provides insights into polynitrogen arrangements at extreme densities., Published by APS, College Park, Md.