| 1. |
- Dubrovinsky, L., et al.
(författare)
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The most incompressible metal osmium at static pressures above 750 gigapascals
- 2015
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Ingår i: Nature. - : NATURE PUBLISHING GROUP. - 0028-0836 .- 1476-4687. ; 525:7568, s. 226-
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Tidskriftsartikel (refereegranskat)abstract
- Metallic osmium (Os) is one of the most exceptional elemental materials, having, at ambient pressure, the highest known density and one of the highest cohesive energies and melting temperatures(1). It is also very incompressible(2-4), but its high-pressure behaviour is not well understood because it has been studied(2-6) so far only at pressures below 75 gigapascals. Here we report powder X-ray diffraction measurements on Os at multi-megabar pressures using both conventional and double-stage diamond anvil cells(7), with accurate pressure determination ensured by first obtaining self-consistent equations of state of gold, platinum, and tungsten in static experiments up to 500 gigapascals. These measurements allow us to show that Os retains its hexagonal close-packed structure upon compression to over 770 gigapascals. But although its molar volume monotonically decreases with pressure, the unit cell parameter ratio of Os exhibits anomalies at approximately 150 gigapascals and 440 gigapascals. Dynamical mean-field theory calculations suggest that the former anomaly is a signature of the topological change of the Fermi surface for valence electrons. However, the anomaly at 440 gigapascals might be related to an electronic transition associated with pressure-induced interactions between core electrons. The ability to affect the core electrons under static high-pressure experimental conditions, even for incompressible metals such as Os, opens up opportunities to search for new states of matter under extreme compression.
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| 2. |
- Zayed, M. E., et al.
(författare)
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Temperature dependence of the pressure induced monoclinic distortion in the spin S=1/2 Shastry-Sutherland compound SrCu2(BO3)(2)
- 2014
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Ingår i: Solid State Communications. - : Elsevier BV. - 0038-1098 .- 1879-2766. ; 186, s. 13-17
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the monoclinic distortion that occurs at 4.7 GPa at room temperature in the frustrated Shastry-Sutherland model quantum magnet SrCu2(BO3)(2) as a function of pressure and temperature by means of powder and single crystal angle dispersive synchrotron X-ray diffraction. Our results indicate that the onset of the structural distortion varies in a narrow pressure range between 4.0 and 5.0 GPa. This result will be useful in order to distinguish between magnetic transitions related to structural changes and potential intrinsic quantum phase transitions that various reports have suggested to take place in SrCu2(BO3)(2) at high pressure and low temperature.
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| 3. |
- Bykova, E., et al.
(författare)
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Metastable silica high pressure polymorphs as structural proxies of deep Earth silicate melts
- 2018
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Ingår i: Nature Communications. - : NATURE PUBLISHING GROUP. - 2041-1723. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Modelling of processes involving deep Earth liquids requires information on their structures and compression mechanisms. However, knowledge of the local structures of silicates and silica (SiO2) melts at deep mantle conditions and of their densification mechanisms is still limited. Here we report the synthesis and characterization of metastable high-pressure silica phases, coesite-IV and coesite-V, using in situ single-crystal X-ray diffraction and ab initio simulations. Their crystal structures are drastically different from any previously considered models, but explain well features of pair-distribution functions of highly densified silica glass and molten basalt at high pressure. Built of four, five-, and six-coordinated silicon, coesite-IV and coesite-V contain SiO6 octahedra, which, at odds with 3rd Paulings rule, are connected through common faces. Our results suggest that possible silicate liquids in Earths lower mantle may have complex structures making them more compressible than previously supposed.
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| 4. |
- Glazyrin, K., et al.
(författare)
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Importance of Correlation Effects in hcp Iron Revealed by a Pressure-Induced Electronic Topological Transition
- 2013
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 110:11, s. 117206-
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Tidskriftsartikel (refereegranskat)abstract
- We discover that hcp phases of Fe and Fe0.9Ni0.1 undergo an electronic topological transition at pressures of about 40 GPa. This topological change of the Fermi surface manifests itself through anomalous behavior of the Debye sound velocity, c/a lattice parameter ratio, and Mossbauer center shift observed in our experiments. First-principles simulations within the dynamic mean field approach demonstrate that the transition is induced by many-electron effects. It is absent in one-electron calculations and represents a clear signature of correlation effects in hcp Fe.
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| 5. |
- Dewaele, A., et al.
(författare)
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High-pressure high-temperature equation of state of KCl and KBr
- 2012
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 85:21, s. 214105-
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Tidskriftsartikel (refereegranskat)abstract
- The equation of state of KCl and KBr, compressed in a helium pressure medium in a diamond-anvil cell, has been measured by x-ray diffraction in the B1 and B2 phases up to 165 GPa at 298 K. The P-V-T of B2 KCl and B2 KBr has been calculated by ab initio molecular dynamics in a wide compression range and up to 7000 K. The thermal pressure exhibits a linear behavior with temperature and remains low under high compression. The experimental P-V points and the thermal pressure calculated by molecular dynamics have been used to set up a high-pressure high-temperature equation of state of B2 KCl and B2 KBr. With these equations of state, B2 KCl and B2 KBr can be used as pressure markers in laser-heated diamond-anvil-cell experiments.
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| 6. |
- Dinnebier, RE, et al.
(författare)
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Bulk moduli and high-pressure crystal structures of minium, Pb3O4, determined by X-ray powder diffraction
- 2003
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Ingår i: American Mineralogist. - 0003-004X. ; 88:7, s. 996-1002
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Tidskriftsartikel (refereegranskat)abstract
- We report the pressure dependence of the crystal structure of lead tetroxide (P less than or equal to 41.05 GPa, T 298 K) using high-resolution angle-dispersive X-ray powder diffraction. Pb3O4 shows two reversible phase transitions in the measured pressure range. The crystal structures of the modifications identified have in common frameworks of Pb+4O6 octahedra and irregular Pb+2O4+1 respectively Pb2+O6+1 polyhedra. At ambient conditions, Pb3O4 crystallizes in space group P4(2)/mbc (phase 1). Between 0.11 and 0.3 GPa it exhibits a displacive second order phase transition to a structure with space group Pbam (phase II). A second displacive phase transition occurs between 5.54 and 6.6 GPa to another structure with space group Pbam (phase 111) but halved c dimension. A non-linear compression behavior over the entire pressure range is observed, which can be described by two Vinet relations in the ranges from 0.28 to 5.54 GPa and from 6.6 to 41.05 GPa. The extrapolated bulk moduli of the high-pressure phases were determined to be K-0 = 21(2) GPa for phase 11 and K-0 = 91(3) GPa for phase III. The crystal structures of all phases were refined from X-ray diffraction powder data collected at several pressures between 0.06 and 41.05 GPa. Except for their cell dimensions, phases I and 11 were found to be isostructural to the corresponding phases at low temperatures, whereas phase III can be derived from the Sr2PbO4 aristotype. With increasing pressure, the lone pair which is localized at Pb2+ adopts increasingly pure s-character, which is reflected by the similar coordination polyhedra of Ph2+ in Pb3O4 (phase 111) and of Sr2+ in Sr2PbO4.
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| 7. |
- Isaev, Eyvas, et al.
(författare)
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Impact of lattice vibrations on equation of state of the hardest boron phase
- 2011
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 83:13, s. 132106-
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Tidskriftsartikel (refereegranskat)abstract
- An accurate equation of state (EOS) is determined for the high-pressure orthorhombic phase of boron, B(28), experimentally as well as from ab initio calculations. The unique feature of our experiment is that it is carried out on the single crystal of B(28). In theory, we take into consideration the lattice vibrations, often neglected in first-principles simulations. We show that the phonon contribution has a profound effect on the EOS of B(28), giving rise to anomalously low values of the pressure derivative of the bulk modulus and greatly improving the agreement between theory and experiment.
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| 8. |
- Koemets, E., et al.
(författare)
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Revealing the Complex Nature of Bonding in the Binary High-Pressure Compound FeO2
- 2021
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Ingår i: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 126:10
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Tidskriftsartikel (refereegranskat)abstract
- Extreme pressures and temperatures are known to drastically affect the chemistry of iron oxides, resulting in numerous compounds forming homologous series nFeOmFe(2)O(3) and the appearance of FeO2. Here, based on the results of in situ single-crystal x-ray diffraction, Mossbauer 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.
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| 9. |
- Arulraj, A, et al.
(författare)
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Shear strain in Nd0.5Ca0.5MnO3 at high pressures
- 2005
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Ingår i: Physical Review Letters. - 1079-7114. ; 94:16, s. 29-31
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Tidskriftsartikel (refereegranskat)abstract
- High-pressure x-ray powder diffraction has been measured on the half doped rare earth manganite Nd0.5Ca0.5MnO3 up to a pressure of 15 GPa. We report the presence of a quantifiable amount of shear distortion of the MnO6 octahedra in Nd0.5Ca0.5MnO3 at high pressures. The lattice strain of Nd0.5Ca0.5MnO3 is minimal at a crossover pressure of p*similar to 7 GPa, with the same lattice strain above and below this pressure achieved by shear and Jahn-Teller-type distortions, respectively. The increase in shear strain with increasing pressure provides a mechanism for the insulating behavior of manganites at high pressures that has not been considered before.
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| 10. |
- Fedotenko, T., et al.
(författare)
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Synthesis of palladium carbides and palladium hydride in laser heated diamond anvil cells
- 2020
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Ingår i: Journal of Alloys and Compounds. - : ELSEVIER SCIENCE SA. - 0925-8388 .- 1873-4669. ; 844
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Tidskriftsartikel (refereegranskat)abstract
- The diamond anvil cell (DAC) technique is a powerful method for the synthesis and studying of novel materials at extreme conditions. In this work we report on high-pressure high-temperature (HPHT) synthesis of palladium carbides (PdCx) and palladium hydride (PdH) in a laser heated diamond anvil cell. Formation of PdCx with a face-centered cubic (fcc) structure resulted from a chemical reaction of Pd with carbon from the diamond anvils at a pressure of about 50 GPa and temperature of 2500-3000 K. The samples were analyzed in situ using synchrotron X-ray diffraction. The compressional behavior of PdC0.19(3) and PdC0.17(3), was studied on decompression. The fit of the pressure-volume data using the 3rd order Birch-Murnaghan equation of state gave the following parameters: V-0 = 65.1 (1) angstrom 3, K-0 = 241 (9) GPa and K-0 = 2.1 (3) for PdC0.19(3), and V-0 = 64.51 (5) angstrom(3), K-0 = 189 (8) GPa and K-0 = 4.5 (4) for PdC0.17(3). The palladium hydride PdH was synthesized at P = 39 (2) GPa and T = 1500 (200) K through a direct reaction of Pd with paraffin oil. (C) 2020 Elsevier B.V. All rights reserved.
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