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1.	Dubrovinsky, Leonid, et al. (författare) Materials synthesis at terapascal static pressures 2022 Ingår i: Nature. - London, United Kingdom : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 605:7909, s. 274-278 Tidskriftsartikel (refereegranskat)abstract Theoretical modelling predicts very unusual structures and properties of materials at extreme pressure and temperature conditions(1,2). 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 cell(3), producing a rhenium-nitrogen alloy and achieving the synthesis of rhenium nitride Re7N3-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.
2.	Pakhomova, Anna, et al. (författare) Penta- and hexa-coordinated beryllium and phosphorus in high-pressure modifications of CaBe2P2O8 2019 Ingår i: Nature Communications. - : NATURE PUBLISHING GROUP. - 2041-1723. ; 10 Tidskriftsartikel (refereegranskat)abstract Beryllium oxides have been extensively studied due to their unique chemical properties and important technological applications. Typically, in inorganic compounds beryllium is tetrahedrally coordinated by oxygen atoms. Herein based on results of in situ single crystal X-ray diffraction studies and ab initio calculations we report on the high-pressure behavior of CaBe2P2O8, to the best of our knowledge the first compound showing a step-wise transition of Be coordination from tetrahedral (4) to octahedral (6) through trigonal bipyramidal (5). It is remarkable that the same transformation route is observed for phosphorus. Our theoretical analysis suggests that the sequence of structural transitions of CaBe2P2O8 is associated with the electronic transformation from predominantly molecular orbitals at low pressure to the state with overlapping electronic clouds of anions orbitals.
3.	Akbar, Fariia Iasmin, et al. (författare) High-pressure synthesis of dysprosium carbides 2023 Ingår i: Frontiers in Chemistry. - : FRONTIERS MEDIA SA. - 2296-2646. ; 11 Tidskriftsartikel (refereegranskat)abstract Chemical reactions between dysprosium and carbon were studied in laser-heated diamond anvil cells at pressures of 19, 55, and 58 GPa and temperatures of similar to 2500 K. In situ single-crystal synchrotron X-ray diffraction analysis of the reaction products revealed the formation of novel dysprosium carbides, Dy4C3 and Dy3C2, and dysprosium sesquicarbide Dy2C3 previously known only at ambient conditions. The structure of Dy4C3 was found to be closely related to that of dysprosium sesquicarbide Dy2C3 with the Pu2C3-type structure. Ab initio calculations reproduce well crystal structures of all synthesized phases and predict their compressional behavior in agreement with our experimental data. Our work gives evidence that high-pressure synthesis conditions enrich the chemistry of rare earth metal carbides.
4.	Aprilis, Georgios, et al. (författare) The Effect of Pulsed Laser Heating on the Stability of Ferropericlase at High Pressures 2020 Ingår i: Minerals. - : MDPI. - 2075-163X. ; 10:6 Tidskriftsartikel (refereegranskat)abstract It is widely accepted that the lower mantle consists of mainly three major minerals-ferropericlase, bridgmanite and calcium silicate perovskite. Ferropericlase ((Mg,Fe)O) is the second most abundant of the three, comprising approximately 16-20 wt% of the lower mantle. The stability of ferropericlase at conditions of the lowermost mantle has been highly investigated, with controversial results. Amongst other reasons, the experimental conditions during laser heating (such as duration and achieved temperature) have been suggested as a possible explanation for the discrepancy. In this study, we investigate the effect of pulsed laser heating on the stability of ferropericlase, with a geochemically relevant composition of Mg0.76Fe0.24O (Fp24) at pressure conditions corresponding to the upper part of the lower mantle and at a wide temperature range. We report on the decomposition of Fp24 with the formation of a high-pressure (Mg,Fe)(3)O(4)phase with CaTi2O4-type structure, as well as the dissociation of Fp24 into Fe-rich and Mg-rich phases induced by pulsed laser heating. Our results provide further arguments that the chemical composition of the lower mantle is more complex than initially thought, and that the compositional inhomogeneity is not only a characteristic of the lowermost part, but includes depths as shallow as below the transition zone.
5.	Aslandukov, Andrey, et al. (författare) Stabilization Of The CN35− Anion In Recoverable High-pressure Ln3O2(CN3) (Ln=La, Eu, Gd, Tb, Ho, Yb) Oxoguanidinates 2023 Ingår i: Angewandte Chemie International Edition. - : WILEY-V C H VERLAG GMBH. - 1433-7851 .- 1521-3773. ; 62:47 Tidskriftsartikel (refereegranskat)abstract A series of isostructural Ln(3)O(2)(CN3) (Ln=La, Eu, Gd, Tb, Ho, Yb) oxoguanidinates was synthesized under high-pressure (25-54 GPa) high-temperature (2000-3000 K) conditions in laser-heated diamond anvil cells. The crystal structure of this novel class of compounds was determined via synchrotron single-crystal X-ray diffraction (SCXRD) as well as corroborated by X-ray absorption near edge structure (XANES) measurements and density functional theory (DFT) calculations. The Ln(3)O(2)(CN3) solids are composed of the hitherto unknown CN35- guanidinate anion-deprotonated guanidine. Changes in unit cell volumes and compressibility of Ln(3)O(2)(CN3) (Ln=La, Eu, Gd, Tb, Ho, Yb) compounds are found to be dictated by the lanthanide contraction phenomenon. Decompression experiments show that Ln(3)O(2)(CN3) compounds are recoverable to ambient conditions. The stabilization of the CN35- guanidinate anion at ambient conditions provides new opportunities in inorganic and organic synthetic chemistry.
6.	Aslandukova, Alena, et al. (författare) Diverse high-pressure chemistry in Y-NH3BH3 and Y–paraffin oil systems 2024 Ingår i: Science Advances. - : AMER ASSOC ADVANCEMENT SCIENCE. - 2375-2548. ; 10:11 Tidskriftsartikel (refereegranskat)abstract The yttrium-hydrogen system has gained attention because of near-ambient temperature superconductivity reports in yttrium hydrides at high pressures. We conducted a study using synchrotron single-crystal x-ray diffraction (SCXRD) at 87 to 171 GPa, resulting in the discovery of known (two YH3 phases) and five previously unknown yttrium hydrides. These were synthesized in diamond anvil cells by laser heating yttrium with hydrogen-rich precursors-ammonia borane or paraffin oil. The arrangements of yttrium atoms in the crystal structures of new phases were determined on the basis of SCXRD, and the hydrogen content estimations based on empirical relations and ab initio calculations revealed the following compounds: Y3H11, Y2H9, Y4H23, Y13H75, and Y4H25. The study also uncovered a carbide (YC2) and two yttrium allotropes. Complex phase diversity, variable hydrogen content in yttrium hydrides, and their metallic nature, as revealed by ab initio calculations, underline the challenges in identifying superconducting phases and understanding electronic transitions in high-pressure synthesized materials.
7.	Bruening, Lukas, et al. (författare) Stabilization of Guanidinate Anions [CN3]5− in Calcite-Type SbCN3 2023 Ingår i: Angewandte Chemie International Edition. - : WILEY-V C H VERLAG GMBH. - 1433-7851 .- 1521-3773. ; 62:47 Tidskriftsartikel (refereegranskat)abstract The stabilization of nitrogen-rich phases presents a significant chemical challenge due to the inherent stability of the dinitrogen molecule. This stabilization can be achieved by utilizing strong covalent bonds in complex anions with carbon, such as cyanide CN- and NCN(2- )carbodiimide, while more nitrogen-rich carbonitrides are hitherto unknown. Following a rational chemical design approach, we synthesized antimony guanidinate SbCN3 at pressures of 32-38 GPa using various synthetic routes in laser-heated diamond anvil cells. SbCN3, which is isostructural to calcite CaCO3, can be recovered under ambient conditions. Its structure contains the previously elusive guanidinate anion [CN3](5-), marking a fundamental milestone in carbonitride chemistry. The crystal structure of SbCN3 was solved and refined from synchrotron single-crystal X-ray diffraction data and was fully corroborated by theoretical calculations, which also predict that SbCN3 has a direct band gap with the value of 2.20 eV. This study opens a straightforward route to the entire new family of inorganic nitridocarbonates.
8.	Bykov, Maxim, et al. (författare) High-Pressure Synthesis of a Nitrogen-Rich Inclusion Compound ReN8·xN2 with Conjugated Polymeric Nitrogen Chains 2018 Ingår i: Angewandte Chemie International Edition. - : WILEY-V C H VERLAG GMBH. - 1433-7851 .- 1521-3773. ; 57:29, s. 9048-9053 Tidskriftsartikel (refereegranskat)abstract A nitrogen-rich compound, ReN(8)xN(2), was synthesized by a direct reaction between rhenium and nitrogen at high pressure and high temperature in a laser-heated diamond anvil cell. Single-crystal X-ray diffraction revealed that the crystal structure, which is based on the ReN8 framework, has rectangular-shaped channels that accommodate nitrogen molecules. Thus, despite a very high synthesis pressure, exceeding 100GPa, ReN(8)xN(2) is an inclusion compound. The amount of trapped nitrogen (x) depends on the synthesis conditions. The polydiazenediyl chains [-N=N-] that constitute the framework have not been previously observed in any compound. Abinitio calculations on ReN(8)xN(2) provide strong support for the experimental results and conclusions.
9.	Bykov, Maxim, et al. (författare) High-Pressure Synthesis of Dirac Materials: Layered van der Waals Bonded BeN4 Polymorph 2021 Ingår i: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 126:17 Tidskriftsartikel (refereegranskat)abstract 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 BeN4. A triclinic phase of beryllium tetranitride tr-BeN4 was synthesized from elements at similar to 85 GPa. Upon decompression to ambient conditions, it transforms into a compound with atomic-thick BeN4 layers interconnected via weak van der Waals bonds and consisting of polyacetylene-like nitrogen chains with conjugated pi systems and Be atoms in square-planar coordination. Theoretical calculations for a single BeN4 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 BeN4 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.
10.	Bykov, Maxim, et al. (författare) High-Pressure Synthesis of Metal-Inorganic Frameworks Hf4N20 center dot N-2, WN8 center dot N-2, and Os5N28 center dot 3 N-2 with Polymeric Nitrogen Linkers 2020 Ingår i: Angewandte Chemie International Edition. - : WILEY-V C H VERLAG GMBH. - 1433-7851 .- 1521-3773. ; 59:26, s. 10321-10326 Tidskriftsartikel (refereegranskat)abstract 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 N2, WN 8 center dot N2, and Os5N28 center dot 3N2 via direct reactions between elements in a diamond anvil cell at pressures exceeding 100 GPa is reported. The porous frameworks (Hf4N20, WN 8, and Os5N28) are built from transition-metal atoms linked either by polymeric polydiazenediyl (polyacetylene-like) nitrogen chains or through dinitrogen units. Triply bound dinitrogen molecules occupy channels of these frameworks. Owing to conjugated polydiazenediyl chains, these compounds exhibit metallic properties. The high-pressure reaction between Hf and N2 also leads to a non-centrosymmetric polynitride Hf2N11 that features double-helix catenapoly[tetraz-1-ene-1,4-diyl] nitrogen chains [-N-N-N=N-](infinity.)
11.	Bykov, Maxim, et al. (författare) High-pressure synthesis of ultraincompressible hard rhenium nitride pernitride Re-2(N-2)(N)(2) stable at ambient conditions 2019 Ingår i: Nature Communications. - : NATURE PUBLISHING GROUP. - 2041-1723. ; 10 Tidskriftsartikel (refereegranskat)abstract High-pressure synthesis in diamond anvil cells can yield unique compounds with advanced properties, but often they are either unrecoverable at ambient conditions or produced in quantity insufficient for properties characterization. Here we report the synthesis of metallic, ultraincompressible (K-0 = 428(10) GPa), and very hard (nanoindentation hardness 36.7(8) GPa) rhenium nitride pernitride Re-2(N-2)(N)(2). Unlike known transition metals pernitrides Re-2(N-2)(N)(2) contains both pernitride N-2(4-) and discrete N3- anions, which explains its exceptional properties. Re-2(N-2)(N)(2) can be obtained via a reaction between rhenium and nitrogen in a diamond anvil cell at pressures from 40 to 90 GPa and is recoverable at ambient conditions. We develop a route to scale up its synthesis through a reaction between rhenium and ammonium azide, NH4N3, in a large-volume press at 33 GPa. Although metallic bonding is typically seen incompatible with intrinsic hardness, Re-2(N-2)(N)(2) turned to be at a threshold for superhard materials.
12.	Bykov, Maxim, et al. (författare) Realization of an Ideal Cairo Tessellation in Nickel Diazenide NiN2: High-Pressure Route to Pentagonal 2D Materials 2021 Ingår i: ACS Nano. - : AMER CHEMICAL SOC. - 1936-0851 .- 1936-086X. ; 15:8, s. 13539-13546 Tidskriftsartikel (refereegranskat)abstract Most of the studied two-dimensional (2D) materials are based on highly symmetric hexagonal structural motifs. In contrast, lower-symmetry structures may have exciting anisotropic properties leading to various applications in nano-electronics. In this work we report the synthesis of nickel diazenide NiN2 which possesses atomic-thick layers comprised of Ni2N3 pentagons forming Cairo-type tessellation. The layers of NiN2 are weakly bonded with the calculated exfoliation energy of 0.72 J/m(2), which is just slightly larger than that of graphene. The compound crystallizes in the space group of the ideal Cairo tiling (P4/mbm) and possesses significant anisotropy of elastic properties. The single-layer NiN2 is a direct-band-gap semiconductor, while the bulk material is metallic. This indicates the promise of NiN2 to be a precursor of a pentagonal 2D material with a tunable direct band gap.
13.	Bykov, Maxim, et al. (författare) Stabilization of Polynitrogen Anions in Tantalum-Nitrogen Compounds at High Pressure 2021 Ingår i: Angewandte Chemie International Edition. - : WILEY-V C H VERLAG GMBH. - 1433-7851 .- 1521-3773. ; 60:16, s. 9003-9008 Tidskriftsartikel (refereegranskat)abstract The synthesis of polynitrogen compounds is of great importance due to their potential as high-energy-density materials (HEDM), but because of the intrinsic instability of these compounds, their synthesis and stabilization is a fundamental challenge. Polymeric nitrogen units which may be stabilized in compounds with metals at high pressure are now restricted to non-branched chains with an average N-N bond order of 1.25, limiting their HEDM performances. Herein, we demonstrate the synthesis of a novel polynitrogen compound TaN5 via a direct reaction between tantalum and nitrogen in a diamond anvil cell at circa 100 GPa. TaN5 is the first example of a material containing branched all-single-bonded nitrogen chains [N-5(5-)](infinity). Apart from that we discover two novel Ta-N compounds: TaN4 with finite N-4(4-) chains and the incommensurately modulated compound TaN2-x, which is recoverable at ambient conditions.
14.	Bykova, Elena, et al. (författare) Novel Class of Rhenium Borides Based on Hexagonal Boron Networks Interconnected by Short B-2 Dumbbells 2022 Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 34:18, s. 8138-8152 Tidskriftsartikel (refereegranskat)abstract Transition metal borides are known due to their attractive mechanical, electronic, refractive, and other properties. A new class of rhenium borides was identified by synchrotron single-crystal X-ray diffraction experiments in laser-heated diamond anvil cells between 26 and 75 GPa. Recoverable to ambient conditions, compounds rhenium triboride (ReB3) and rhenium tetraboride (ReB4) consist of close-packed single layers of rhenium atoms alternating with boron networks built from puckered hexagonal layers, which link short bonded (similar to 1.7 angstrom) axially oriented B-2 dumbbells. The short and incompressible Re-B and B-B bonds oriented along the hexagonal c-axis contribute to low axial compressibility comparable with the linear compressibility of diamond. Sub-millimeter samples of ReB3 and ReB4 were synthesized in a large-volume press at pressures as low as 33 GPa and used for material characterization. Crystals of both compounds are metallic and hard (Vickers hardness, H-V = 34(3) GPa). Geometrical, crystal-chemical, and theoretical analysis considerations suggest that potential ReBx compounds with x > 4 can be based on the same principle of structural organization as in ReB3 and ReB4 and possess similar mechanical and electronic properties.
15.	Bykova, Elena, et al. (författare) Synthesis, crystal structure, and properties of stoichiometric hard tungsten tetraboride, WB4 2022 Ingår i: Journal of Materials Chemistry A. - : ROYAL SOC CHEMISTRY. - 2050-7488 .- 2050-7496. ; 10:37, s. 20111-20120 Tidskriftsartikel (refereegranskat)abstract Tungsten tetraboride has been known so far as a non-stoichiometric compound with a variable composition (e.g. WB4-x, WB4+x). Its mechanical properties could exceed those of hard tungsten carbide, which is widely used nowadays in science and technology. The existence of stoichiometric WB4 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 WB4 phase under high-pressure high-temperature conditions. The crystal structure of WB4 was determined using synchrotron single-crystal X-ray diffraction. In situ high-pressure compressibility measurements show that the bulk modulus of WB4 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 similar to 36 GPa, confirming that the material falls in the category of superhard materials.
16.	Jönsson, Johan, et al. (författare) Inverse pressure-induced Mott transition in TiPO4 2019 Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 99:24 Tidskriftsartikel (refereegranskat)abstract TiPO4 shows interesting structural and magnetic properties as temperature and pressure are varied, such as a spin-Peierls phase transition and the development of incommensurate modulations of the lattice. Recently, high-pressure experiments for TiPO4 reported two structural phases appearing at high pressures, the so-called phases IV and V [M. Bykov et al., Angew. Chem. Int. Ed. 55, 15053 (2016).]. The latter was shown to include the first example of fivefold O-coordinated P atoms in an inorganic phosphate compound. In this work, we characterize the electronic structure and other physical properties of these phases by means of ab initio calculations and investigate the structural transition. We find that the appearance of phases IV and V coincides with a collapse of the Mott insulating gap and quenching of magnetism in phase III as pressure is applied. Remarkably, our calculations show that in the high-pressure phase V, these features reappear, leading to an antiferromagnetic Mott insulating phase, with robust local moments.
17.	Khandarkhaeva, Saiana, et al. (författare) Novel Rhenium Carbides at 200 GPa 2020 Ingår i: European Journal of Inorganic Chemistry. - : WILEY-V C H VERLAG GMBH. - 1434-1948 .- 1099-1948 .- 1099-0682. ; 2020:22, s. 2186-2190 Tidskriftsartikel (refereegranskat)abstract Laser heating of rhenium in a diamond anvil cell to 3000 +/- 300 K at about 200 GPa results in formation of two previously unknown rhenium carbides, hexagonal WC-type structured ReC and orthorhombic TiSi2-type structured ReC2. The shortest C-C distances [1.758(3) angstrom at 219(5) GPa and 1.850(4) angstrom at 180(7) GPa] found in honeycomb-like carbon nets in the structure of ReC2 are quite unusual. The Re-C solid solution formed at multimegabar pressure has the carbon content of approximate to 20 at%.
18.	Khandarkhaeva, Saiana, et al. (författare) Testing the performance of secondary anvils shaped with focused ion beam from the single-crystal diamond for use in double-stage diamond anvil cells 2022 Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 93:3 Tidskriftsartikel (refereegranskat)abstract 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.
19.	Laniel, Dominique, et al. (författare) High Pressure Investigation of the S-N-2 System up to the Megabar Range: Synthesis and Characterization of the SN2 Solid 2019 Ingår i: Inorganic Chemistry. - : AMER CHEMICAL SOC. - 0020-1669 .- 1520-510X. ; 58:14, s. 9195-9204 Tidskriftsartikel (refereegranskat)abstract Sulfur and nitrogen represent one of the most studied inorganic binary systems at ambient pressure on account of their large wealth of metastable exotic ring-like compounds. Under high pressure conditions, however, their behavior is unknown. Here, sulfur and nitrogen were compressed in a diamond anvil cell up to about 120 GPa and laser-heated at regular pressure intervals in an attempt to stabilize novel sulfur nitrogen compounds. Above 64 GPa, an orthorhombic (space group Pnnm) SN2 compound was synthesized and characterized by single-crystal and powder X-ray diffraction as well as Raman spectroscopy. It is shown to adopt a CaCl2-type structure hence it is isostructural, isomassic, and isoelectronic to CaCl2-type SiO2 comprised of SN6 octahedra. Complementary theoretical calculations were performed to provide further insight into the physicochemical properties of SN2, notably its equation of state, the bonding type between its constitutive elements, and its electronic density of states. This new solid is shown to be metastable down to about 20 GPa, after which it spontaneously decomposes into S and N-2. This investigation shows that despite the many metastable S N compounds existing at ambient conditions, none of them are formed by pressure.
20.	Laniel, Dominique, et al. (författare) High-pressure Na-3(N-2)(4), Ca-3(N-2)(4), Sr-3(N-2)(4), and Ba(N-2)(3) featuring nitrogen dimers with noninteger charges and anion-driven metallicity 2022 Ingår i: Physical Review Materials. - : AMER PHYSICAL SOC. - 2475-9953. ; 6:2 Tidskriftsartikel (refereegranskat)abstract Charged molecular species, such as [N-2](x-), [O-2](x-), [C-2](x-), and [S-2](x-), follow the paradigm of carrying integer values of electrons. Here, the Na-3(N-2)(4), Ca-3(N-2)(4), Sr-3(N-2)(4), and Ba(N-2)(3) compounds were produced and characterized <70 GPa and evidenced to be composed of paradigm-breaking [N-2](x-) dimers with noninteger charges of -0.75, -1.5, -1.5, and -0.67, respectively. The anion-driven metallicity of the compounds is proposed as the physical mechanism enabling the noninteger electron count of the [N-2](x-) dimers. The properties of these dimers and the compounds bearing them are demonstrated to depend on their noninteger charge, paving the way to materials with electron-tunable features.
21.	Laniel, Dominique, et al. (författare) Novel sulfur hydrides synthesized at extreme conditions 2020 Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 102:13 Tidskriftsartikel (refereegranskat)abstract The sulfur-hydrogen system is the first one in which superconductivity at temperatures over 200 K has been reported, albeit at high pressure. The particular phases causing the measured T-c and their structures are not yet firmly identified. Here, synchrotron single-crystal x-ray diffraction studies of S-H samples were performed up to 150 GPa and revealed two previously unobserved and unpredicted sulfur-hydrogen phases-H6 +/- xS5 with x similar to 0.4, and H2.85 +/- yS2 with y similar to 0.35. The crystallographic data obtained in this work, both for the new phases and for the previously identified H3S polymorphs, provide an unambiguous experimental proof of the chemical richness of the S-H system and the structural diversity of compounds forming at high pressures and high temperatures. Our results have profound implications for the interpretation of the resistance, superconductivity, and other physical properties measurements on the complex S-H system.
22.	Liang, Akun, et al. (författare) High-Pressure Synthesis of Ultra-Incompressible, Hard and Superconducting Tungsten Nitrides 2024 Ingår i: Advanced Functional Materials. - : WILEY-V C H VERLAG GMBH. - 1616-301X .- 1616-3028. Tidskriftsartikel (refereegranskat)abstract Transition metal nitrides, particularly those of 5d metals, are known for their outstanding properties, often relevant for industrial applications. Among these metal elements, tungsten is especially attractive given its low cost. In this high-pressure investigation of the W-N system, two novel ultra-incompressible tungsten nitride superconductors, namely W2N3 and W3N5, are successfully synthesized at 35 and 56 GPa, respectively, through a direct reaction between N2 and W in laser-heated diamond anvil cells. Their crystal structure is determined using synchrotron single-crystal X-ray diffraction. While the W2N3 solid's sole constituting nitrogen species are N3- units, W3N5 features both discrete N3- as well as N24- pernitride anions. The bulk modulus of W2N3 and W3N5 is experimentally determined to be 380(3) and 406(7) GPa, and their ultra-incompressible behavior is rationalized by their constituting WN7 polyhedra and their linkages. Importantly, both W2N3 and W3N5 are recoverable to ambient conditions and stable in air. Density functional theory calculations reveal W2N3 and W3N5 to have a Vickers hardness of 30 and 34 GPa, and superconducting transition temperatures at ambient pressure (50 GPa) of 11.6 K (9.8 K) and 9.4 K (7.2 K), respectively. Additionally, transport measurements performed at 50 GPa on W2N3 corroborate with the calculations. Two recoverable tungsten nitrides, namely W2N3 and W3N5, are synthesized using laser-heated diamond anvil cells. Both compounds exhibit a high bulk modulus, hardness, and superconducting transition temperature. image
23.	Meier, Thomas, et al. (författare) Proton mobility in metallic copper hydride from high-pressure nuclear magnetic resonance 2020 Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 102:16 Tidskriftsartikel (refereegranskat)abstract The atomic and electronic structures of Cu2H 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 Cu2H was synthesized at a pressure of 40 GPa, and semimetallic CuH at 90 GPa, found stable up to 160 GPa. For Cu2H, 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 H-1 mobility of similar to 10(-7) cm(2)/s. A comparison of these observations with results on FeH suggests that they could be common features in metal hydrides.
24.	Tasnadi, Ferenc, et al. (författare) Thermodynamic and electronic properties of ReN2 polymorphs at high pressure 2021 Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 104:17 Tidskriftsartikel (refereegranskat)abstract The high-pressure synthesis of rhenium nitride pernitride with a crystal structure that is unusual for transition metal dinitrides and high values of hardness and bulk modulus attracted significant attention to this system. We investigate the thermodynamic and electronic properties of the P2(1)/c phase of ReN2 and compare them with two other polytypes, the C2/m and P4/mbm phases, suggested in the literature. Our calculations of the formation enthalpy at zero temperature show that the former phase is the most stable of the three up to a pressure p = 170 GPa, followed by the stabilization of the P4/mbm phase at higher pressure. The theoretical prediction is confirmed by diamond anvil cell synthesis of the P4/mbm ReN2 at approximate to 175 GPa. Considering the effects of finite temperature in the quasiharmonic approximation at p = 100 GPa we demonstrate that the P2(1)/c phase has the lowest free energy of formation at least up to 1000 K. Our analysis of the pressure dependence of the electronic structure of rhenium nitride pernitride shows the presence of two electronic topological transitions around 18 GPa, when the Fermi surface changes its topology due to the appearance of an electron pocket at the high-symmetry Y-2 point of the Brillouin zone while the disruption of the neck takes place slightly off from the Gamma-A line.
25.	Yin, Yuqing, et al. (författare) Synthesis of rare-earth metal compounds through enhanced reactivity of alkali halides at high pressures 2022 Ingår i: Communications Chemistry. - : Nature Portfolio. - 2399-3669. ; 5:1 Tidskriftsartikel (refereegranskat)abstract Chemical stability of the alkali halides NaCI and KCI has allowed for their use as inert media in high-pressure high-temperature experiments. Here we demonstrate the unexpected reactivity of the halides with metals (Y, Dy, and Re) and iron oxide (FeO) in a laser-heated diamond anvil cell, thus providing a synthetic route for halogen-containing binary and ternary compounds. So far unknown chlorides, Y2Cl and DyCl, and chloride carbides, Y2ClC and Dy2ClC, were synthesized at -40 GPa and 2000 K and their structures were solved and refined using in situ single-crystal synchrotron X-ray diffraction. Also, FeCl2 with the HP-PdF2-type structure, previously reported at 108 GPa, was synthesized at similar to 160 GPa and 2100 K. The results of our ab initio calculations fully support experimental findings and reveal the electronic structure and chemical bonding in these compounds.
26.	Yin, Yuqing, et al. (författare) Unraveling the Bonding Complexity of Polyhalogen Anions: High-Pressure Synthesis of Unpredicted Sodium Chlorides Na2Cl3 and Na4Cl5 and Bromide Na4Br5 2023 Ingår i: JACS Au. - : AMER CHEMICAL SOC. - 2691-3704. ; 3:6, s. 1634-1641 Tidskriftsartikel (refereegranskat)abstract The field of polyhalogen chemistry, specifically polyhalogenanions(polyhalides), is rapidly evolving. Here, we present the synthesisof three sodium halides with unpredicted chemical compositions andstructures (tP10-Na2Cl3, hP18-Na4Cl5, and hP18-Na4Br5), a series of isostructural cubic cP8-AX(3) halides (NaCl3, KCl3, NaBr3, and KBr3), and a trigonal potassiumchloride (hP24-KCl3). The high-pressuresyntheses were realized at 41-80 GPa in diamond anvil cellslaser-heated at about 2000 K. Single-crystal synchrotron X-ray diffraction(XRD) provided the first accurate structural data for the symmetrictrichloride Cl-3 (-) anion in hP24-KCl3 and revealed the existence of two different typesof infinite linear polyhalogen chains, [Cl]( infinity ) ( n-) and [Br]( infinity ) ( n-), in the structures of cP8-AX(3) compounds and in hP18-Na4Cl5 and hP18-Na4Br5. In Na4Cl5 and Na4Br5, we found unusually short, likely pressure-stabilized, contactsbetween sodium cations. Ab initio calculations support the analysisof structures, bonding, and properties of the studied halogenides.

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