Suchergebnisse

Based on the results from previous high-pressure experiments on the gadolinite-type mineral datolite, CaBSiO4(OH), the behavior of the isostructural borates beta-HfB2O5 and beta-ZrB2O5 have been studied by synchrotron-based in situ high-pressure single-crystal X-ray diffraction experiments. On compression to 120 GPa, both borate layer-structures are preserved. Additionally, at approximate to 114 GPa, the formation of a second phase can be observed in both compounds. The new high-pressure modification gamma-ZrB2O5 features a rearrangement of the corner-sharing BO4 tetrahedra, while still maintaining the four- and eight-membered rings. The new phase gamma-HfB2O5 contains ten-membered rings including the rare structural motif of edge-sharing BO4 tetrahedra with exceptionally short B-O and B.B distances. For both structures, unusually high coordination numbers are found for the transition metal cations, with ninefold coordinated Hf4+, and tenfold coordinated Zr4+, respectively. These findings remarkably show the potential of cold compression as a low-energy pathway to discover metastable structures that exhibit new coordinations and structural motifs. ; Funding Agencies|Federal Ministry of Education and Research, Germany (BMBF)Federal Ministry of Education & Research (BMBF) [05K19WC1]; Deutsche Forschungsgemeinschaft (DFG)German Research Foundation (DFG) [DU 954-11/1, DU 393-9/2, DU 393-13/1]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]

We report the high-pressure synthesis and the equation of state (EOS) of a novel nickel carbide (Ni3C). 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. Ni3C has the cementite-type structure (Pnma space group, a = 4.519(2) angstrom, b = 5.801(2) angstrom, c = 4.009(3) angstrom), which was solved and refined based on in-situ synchrotron single-crystal X-ray diffraction. The pressure-volume data of Ni3C 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) angstrom(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 Earths outer core. ; Funding Agencies|Federal Ministry of Education and Research, Germany (BMBF)Federal Ministry of Education & Research (BMBF) [05K19WC1]; Deutsche Forschungsgemeinschaft (DFG)German Research Foundation (DFG) [DU 954-11/1, DU 393-9/2, DU 393-13/1]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]

At high pressures, autoionization - along with polymerization and metallization - is one of the responses of simple molecular systems to a rise in electron density. Nitrosonium nitrate (NO+NO3-), known for this property, has attracted a large interest in recent decades and was reported to be synthesized at high pressure and high temperature from a variety of nitrogen-oxygen precursors, such as N2O4, N2O and N-2-O-2 mixtures. However, its structure has not been determined unambiguously. Here, we present the first structure solution and refinement for nitrosonium nitrate on the basis of single-crystal X-ray diffraction at 7.0 and 37.0 GPa. The structure model (P2(1)/m space group) contains the triple-bonded NO+ cation and the NO3- sp(2)-trigonal planar anion. Remarkably, crystal-chemical considerations and accompanying density-functional-theory calculations show that the oxygen atom of the NO+ unit is positively charged - a rare occurrence when in the presence of a less-electronegative element. ; Funding Agencies|Alexander von Humboldt FoundationAlexander von Humboldt Foundation; Federal Ministry of Education and Research, Germany (BMBF)Federal Ministry of Education & Research (BMBF) [05K19WC1]; Deutsche Forschungsgemeinschaft (DFG)German Research Foundation (DFG) [DU 954-11/1, DU 393-9/2, DU 393-13/1]; DFGGerman Research Foundation (DFG)European Commission [DFG FOR2125, WI1232]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]

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%. ; Funding Agencies|Federal Ministry of Education and Research, Germany (BMBF)Federal Ministry of Education & Research (BMBF) [5K16WC1, 05K19WC1]; Deutsche Forschungsgemeinschaft (DFG)German Research Foundation (DFG) [DU 954-11/1, DU 393-9/2, DU 393-13/1]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]

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. ; Funding Agencies|Alexander von Humboldt-StiftungAlexander von Humboldt Foundation; Bundesministerium fur Bildung und ForschungFederal Ministry of Education & Research (BMBF) [05K19WC1]; Deutsche ForschungsgemeinschaftGerman Research Foundation (DFG) [DU 954-11/1, DU 393-9/2, DU 393-13/1, FOR2125, WI1232]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]

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. ; Funding Agencies|Federal Ministry of Education and Research, Germany (BMBF)Federal Ministry of Education & Research (BMBF) [5K16WC1, 05K19WC1]; Deutsche Forschungsgemeinschaft (DFG)German Research Foundation (DFG) [DU 954-11/1, DU 393-9/2, DU 393-13/1]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University faculty grant SFO-Mat-LiU [2009 00971]

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.) ; Funding Agencies|National Science Foundation-Earth SciencesNational Science Foundation (NSF) [EAR-1634415]; Department of Energy-GeoSciencesUnited States Department of Energy (DOE) [DE-FG02-94ER14466]; Army Research Office; Deutsche Forschungsgemeinschaft (DFG)German Research Foundation (DFG) [DU 95411/1, DU 393-9/2, DU 393-13/1]; Federal Ministry of Education and Research, Germany (BMBF)Federal Ministry of Education & Research (BMBF) [05K19WC1]; Russian Science FoundationRussian Science Foundation (RSF) [18-12-00492]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkcping University (Faculty Grant SFO-Mat-LiU) [2009 00971]; Knut and AliceWallenberg FoundationKnut & Alice Wallenberg Foundation [KAW-2018.0194]; Swedish Research Council (VR)Swedish Research Council [2019-05600]; VINN Excellence Center Functional Nanoscale Materials (FunMat-2) [2016-05156]; [W911NF-19-2-0172]