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1.	Dubrovinsky, L., et al. (författare) The most incompressible metal osmium at static pressures above 750 gigapascals 2015 Ingår i: Nature. - : NATURE PUBLISHING GROUP. - 0028-0836 .- 1476-4687. ; 525:7568, s. 226- 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.
2.	Glazyrin, K., et al. (författare) Importance of Correlation Effects in hcp Iron Revealed by a Pressure-Induced Electronic Topological Transition 2013 Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 110:11, s. 117206- 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.
3.	Pourovskii, L. V., et al. (författare) Electronic properties and magnetism of iron at the Earth's inner core conditions 2013 Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 87:11, s. 115130- Tidskriftsartikel (refereegranskat)abstract We employ state-of-the-art ab initio simulations within the dynamical mean-field theory to study three likely phases of iron (hcp, fcc, and bcc) at the Earth's core conditions. We demonstrate that the correction to the electronic free energy due to correlations can be significant for the relative stability of the phases. The strongest effect is observed in bcc Fe, which shows a non-Fermi-liquid behavior, and where a Curie-Weiss behavior of the uniform susceptibility hints at a local magnetic moment still existing at 5800 K and 300 GPa. We predict that all three structures have sufficiently high magnetic susceptibility to stabilize the geodynamo.
4.	Ahuja, Rajeev, et al. (författare) Titanium metal at high pressure : Synchrotron experiments and ab initio calculations 2004 Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 69, s. 184102- Tidskriftsartikel (refereegranskat)
5.	Asker, Christian, 1979-, et al. (författare) Equation of state and elastic properties of face-centered cubic FeMg alloy at ultrahigh pressures from first-principles 2010 Ingår i: Earth and Planetary Science Letters. - : Elsevier BV. - 0012-821X .- 1385-013X. ; 293:1-2, s. 130-134 Tidskriftsartikel (refereegranskat)abstract We have ca1culated the equation of state and elastic properties of face-centered cubic Fe and Fe-rich FeMg alloy at ultrahigh pressures from first principles using the Exact Muffin-Tin Orbitals method. The results show that adding Mg into Fe influences strongly the equation of state, and cause a large degree of softening of the elastic constants, even at concentrations as small as 1-2 at. %. Moreover, the e1astic anisotropy increases, and the effect is higher at higher pressures.
6.	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.
7.	Bosak, A., et al. (författare) Possible artifacts in inferring seismic properties from X-ray data 2016 Ingår i: Physics of the Earth and Planetary Interiors. - : ELSEVIER SCIENCE BV. - 0031-9201 .- 1872-7395. ; 260, s. 14-19 Tidskriftsartikel (refereegranskat)abstract We consider the experimental and computational artifacts relevant for the extraction of aggregate elastic properties of polycrystalline materials with particular emphasis on the derivation of seismic velocities. We use the case of iron as an example, and show that the improper use of definitions and neglecting the crystalline anisotropy can result in unexpectedly large errors up to a few percent. (C) 2016 Elsevier B.V. All rights reserved.
8.	Bykov, M., et al. (författare) Fe-N system at high pressure reveals a compound featuring polymeric nitrogen chains 2018 Ingår i: Nature Communications. - : NATURE PUBLISHING GROUP. - 2041-1723. ; 9 Tidskriftsartikel (refereegranskat)abstract Poly-nitrogen compounds have been considered as potential high energy density materials for a long time due to the large number of energetic N-N or N=N bonds. In most cases high nitrogen content and stability at ambient conditions are mutually exclusive, thereby making the synthesis of such materials challenging. One way to stabilize such compounds is the application of high pressure. Here, through a direct reaction between Fe and N-2 in a laser-heated diamond anvil cell, we synthesize three ironnitrogen compounds Fe3N2, FeN2 and FeN4. Their crystal structures are revealed by single-crystal synchrotron X-ray diffraction. Fe3N2, synthesized at 50 GPa, is isostructural to chromium carbide Cr3C2. FeN2 has a marcasite structure type and features covalently bonded dinitrogen units in its crystal structure. FeN4, synthesized at 106 GPa, features polymeric nitrogen chains of [N-4(2-)](n) units. Based on results of structural studies and theoretical analysis, [N-4(2-)](n) units in this compound reveal catena-poly[tetraz-1-ene-1,4-diyl] anions.
9.	Bykova, E., et al. (författare) Metastable silica high pressure polymorphs as structural proxies of deep Earth silicate melts 2018 Ingår i: Nature Communications. - : NATURE PUBLISHING GROUP. - 2041-1723. ; 9 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.
10.	Cerenius, Y, et al. (författare) Compressibility measurements on iridium 2000 Ingår i: JOURNAL OF ALLOYS AND COMPOUNDS. - : ELSEVIER SCIENCE SA. - 0925-8388. ; 306:1-2, s. 26-29 Tidskriftsartikel (refereegranskat)abstract The compressibility of iridium was determined by energy-dispersive X-ray diffraction and synchrotron radiation up to a pressure of 65 GPa in the diamond-anvil cell. The bulk modulus (B-0) was determined to be B-0,=306 (23) with B-0'=6.8 (1.5) when using a
11.	Dubrovinskaia, N.A., et al. (författare) Experimental and theoretical identification of a new high-pressure TiO$_2$ polymorph 2001 Ingår i: Physical Review Letters. - 0031-9007. ; 87:27, s. 275501-1 Tidskriftsartikel (refereegranskat)
12.	Dubrovinskaia, N. A., et al. (författare) Experimental and theoretical identification of a new high-pressure TiO2 polymorph 2001 Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 87, s. 275501-1 Tidskriftsartikel (refereegranskat)
13.	Dubrovinskaia, N., et al. (författare) Beating the miscibility barrier between iron and magnesium by high-pressure alloying 2005 Ingår i: Physical Review Letters. ; 95, s. 245502- Tidskriftsartikel (refereegranskat)
14.	Dubrovinskaia, N., et al. (författare) Beating the miscibility barrier between iron group elements and magnesium by high-pressure alloying 2005 Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 95:24 Tidskriftsartikel (refereegranskat)abstract Iron and magnesium are almost immiscible at ambient pressure. The low solubility of Mg in Fe is due to a very large size mismatch between the alloy components. However, the compressibility of Mg is much higher than that of Fe, and therefore the difference in atomic sizes between elements decreases dramatically with pressure. Based on the predictions of ab initio calculations, we demonstrate in a series of experiments in a multianvil apparatus and in electrically and laser-heated diamond anvil cells that high pressure promotes solubility of magnesium in iron. At the megabar pressure range, more than 10 at. % of Mg can dissolve in Fe and then the alloy can be quenched to ambient conditions. A generality of the concept of high-pressure alloying between immiscible elements is demonstrated by its application to two other Fe group elements, Co and Ni.
15.	Dubrovinskaia, N., et al. (författare) Compressibility of boron-doped diamond 2006 Ingår i: High Pressure Research. - : Informa UK Limited. - 0895-7959 .- 1477-2299. ; 26, No. 2, s. 79-85 Tidskriftsartikel (refereegranskat)
16.	Dubrovinsky, L, et al. (författare) Chemical interaction of Fe and Al2O3 as a source of heterogeneity at the Earth's core-mantle boundary 2001 Ingår i: NATURE. - : MACMILLAN PUBLISHERS LTD. - 0028-0836. ; 412:6846, s. 527-529 Tidskriftsartikel (refereegranskat)abstract Seismological studies have revealed that a complex texture or heterogeneity exists in the Earth's inner core and at the boundary between core and mantle(1-4). These studies highlight the importance of understanding the properties of iron when modelling th
17.	Dubrovinsky, L., et al. (författare) Iron-silica interaction at extreme conditions and the electrically conducting layer at the base of Earth's mantle 2003 Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 422:6927, s. 58-61 Tidskriftsartikel (refereegranskat)abstract The boundary between the Earth's metallic core and its silicate mantle is characterized by strong lateral heterogeneity and sharp changes in density, seismic wave velocities, electrical conductivity and chemical composition(1-7). To investigate the composition and properties of the lowermost mantle, an understanding of the chemical reactions that take place between liquid iron and the complex Mg-Fe-Si-Al-oxides of the Earth's lower mantle is first required(8-15). Here we present a study of the interaction between iron and silica (SiO2) in electrically and laser-heated diamond anvil cells. In a multianvil apparatus at pressures up to 140 GPa and temperatures over 3,800 K we simulate conditions down to the core-mantle boundary. At high temperature and pressures below 40 GPa, iron and silica react to form iron oxide and an iron-silicon alloy, with up to 5 wt% silicon. At pressures of 85-140 GPa, however, iron and SiO2 do not react and iron-silicon alloys dissociate into almost pure iron and a CsCl-structured (B2) FeSi compound. Our experiments suggest that a metallic silicon-rich B2 phase, produced at the core-mantle boundary (owing to reactions between iron and silicate(2,9,10,13)), could accumulate at the boundary between the mantle and core and explain the anomalously high electrical conductivity of this region(6).
18.	Dubrovinsky, L, et al. (författare) Iron-Silica Interaction at Extreme Conditions and the Nature of the Electrically Conducting Layer at the base of Earth's Mantle 2003 Ingår i: Nature. ; 422, s. 58-61 Tidskriftsartikel (refereegranskat)
19.	Dubrovinsky, L., et al. (författare) Noblest of all metals is structurally unstable at high pressure 2007 Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 98:4 Tidskriftsartikel (refereegranskat)abstract In a series of experiments in externally electrically heated diamond anvil cells we demonstrate that at pressures above similar to 240 GPa gold adopts a hexagonal-close-packed structure. Ab initio calculations predict that at pressures about 250 GPa different stacking sequences of close-packed atomic layers in gold become virtually degenerate in energy, strongly supporting the experimental observations.
20.	Dubrovinsky, L., et al. (författare) Pressure-induced invar effect in Fe-Ni alloys 2001 Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 86:21, s. 4851-4854 Tidskriftsartikel (refereegranskat)
21.	Dubrovinsky, L, et al. (författare) Pressure-induced invar effect in Fe-Ni alloys 2001 Ingår i: PHYSICAL REVIEW LETTERS. - 0031-9007. ; 86:21, s. 4851-4854 Tidskriftsartikel (refereegranskat)abstract We have measured the pressure-volume (P-V) relations for cubic iron-nickel alloys for three different compositions: Fe0.64Ni0.36, Fe0.55Ni0.45, and Fe0.20Ni0.80. It is observed that for a certain pressure range the bulk modulus does not change or can even
22.	Dubrovinsky, L., et al. (författare) Relativistic Effects Driven Structural Phase Transition in Gold at High Pressure Ingår i: Nature. Tidskriftsartikel (refereegranskat)
23.	Dubrovinsky, L. S., et al. (författare) Materials science - The hardest known oxide 2001 Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 410:6829, s. 653-654 Tidskriftsartikel (refereegranskat)
24.	Dubrovinsky, L. S., et al. (författare) The structure of the metallic high-pressure Fe3O4 polymorph : experimental and theoretical study 2003 Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 15, s. 7697- Tidskriftsartikel (refereegranskat)
25.	Dubrovinsky, L, et al. (författare) Stability of (Mg0.5Fe0.5)O and (Mg0.8Fe0.2)O magnesiowustites in the lower mantle 2001 Ingår i: EUROPEAN JOURNAL OF MINERALOGY. - : E SCHWEIZERBARTSCHE VERLAGS. - 0935-1221. ; 13:5, s. 857-861 Tidskriftsartikel (refereegranskat)abstract We have heated magnesiowtistites (Mg0.5Fe0.5)O and (Mg0.8Fe0.2)O to temperatures of over 1000 K at pressures of over 80 GPa simulating the stability of the solid solution at physical conditions relevant to the Earth's lower mantle. The X-ray study of the
26.	Dubrovinsky, L, et al. (författare) Theoretical study of the stability of MgSiO3-perovskite in the deep mantle 1998 Ingår i: GEOPHYSICAL RESEARCH LETTERS. - : AMER GEOPHYSICAL UNION. - 0094-8276. ; 25:23, s. 4253-4256 Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract We have used theoretical methods (Full-Potential Linear-muffin-tin-orbital, FPLMTO, and lattice dynamics) to calculate the Gibbs free energy of the phases, perovskite (MgSiO3), SBAD (SiO2), stishovite (SiO2) and periclase (MgO). At 300 K, perovskite is fo
27.	Dubrovinsky, L, et al. (författare) X-ray diffraction under non-hydrostatic conditions in experiments with diamond anvil cell: wustite (FeO) as an example 2000 Ingår i: MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING. - : ELSEVIER SCIENCE SA. - 0921-5093. ; 288:2, s. 187-190 Tidskriftsartikel (refereegranskat)abstract The stress state in a solid specimen compressed between two flat and parallel anvil faces (in a diamond anvil cell, for example) is non-hydrostatic. The resulting lattice strains, measured by X-ray diffraction, exhibit certain features, which are absent i
28.	El, Goresy A, et al. (författare) A monoclinic post-stishovite polymorph of silica in the Shergotty meteorite 2000 Ingår i: SCIENCE. - : AMER ASSOC ADVANCEMENT SCIENCE. - 0036-8075. ; 288:5471, s. 1632-1634 Tidskriftsartikel (refereegranskat)abstract A post-stishovite phase of silica was identified in the Shergotty meteorite by x-ray diffraction and field emission scanning electron microscopy. The diffraction pattern revealed a monoclinic Lattice, similar to the baddeleyite-structured polymorph with t
29.	El, Goresy A, et al. (författare) A new poststishovite silicon dioxide polymorph with the baddelyite structure (zirconium oxide) in the SNC meteorite Shergotty: Evidence for extreme shock pressure 1998 Ingår i: METEORITICS & PLANETARY SCIENCE. - : METEORITICAL SOC. ; 33:4 Annan publikation (övrigt vetenskapligt/konstnärligt)
30.	El, Goresy A, et al. (författare) An ultradense polymorph of rutile with seven-coordinated titanium from the Ries crater 2001 Ingår i: SCIENCE. - : AMER ASSOC ADVANCEMENT SCIENCE. - 0036-8075. ; 293:5534, s. 1467-1470 Tidskriftsartikel (refereegranskat)abstract We report the discovery of an ultradense post-rutile polymorph of titanium dioxide in shocked gneisses of the Ries crater in Germany. The microscopic diagnostic feature is intense blue internal reflections in crossed polarizers in reflected light. X-ray d
31.	Fedotenko, T., et al. (författare) Isothermal equation of state of crystalline and glassy materials from optical measurements in diamond anvil cells 2021 Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 92:6 Tidskriftsartikel (refereegranskat)abstract 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 omega-Ti up to 30 GPa in a Ne pressure transmitting medium. Within the accuracy of the measurements, the bulk modulus of omega-Ti determined using optical microscopy was similar to that obtained from x-ray diffraction. For glassy carbon compressed to similar to 30 GPa, the previously unknown bulk modulus was found to be equal to K-0 = 28 (2) GPa [K = 5.5(5)]. Published under an exclusive license by AIP Publishing.
32.	Fedotenko, T., et al. (författare) Synthesis of palladium carbides and palladium hydride in laser heated diamond anvil cells 2020 Ingår i: Journal of Alloys and Compounds. - : ELSEVIER SCIENCE SA. - 0925-8388 .- 1873-4669. ; 844 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.
33.	Gillet, P, et al. (författare) Natural NaAlSi3O8-hollandite in the shocked Sixiangkou meteorite 2000 Ingår i: SCIENCE. - : AMER ASSOC ADVANCEMENT SCIENCE. - 0036-8075. ; 287:5458, s. 1633-1636 Tidskriftsartikel (refereegranskat)abstract The hollandite high-pressure polymorph of plagioclase has been identified in shock-induced melt veins of the Sixiangkou 16 chondrite. It is intimately intergrown with feldspathic glass within grains previously thought to be "maskelynite." The crystallogra
34.	Glazyrin, K., et al. (författare) Sub-micrometer focusing setup for high-pressure crystallography at the Extreme Conditions beamline at PETRA III 2022 Ingår i: Journal of Synchrotron Radiation. - Chichester, United Kingdom : Wiley-Blackwell. - 0909-0495 .- 1600-5775. ; 29, s. 654-663 Tidskriftsartikel (refereegranskat)abstract Scientific tasks aimed at decoding and characterizing complex systems and processes at high pressures set new challenges for modern X-ray diffraction instrumentation in terms of X-ray flux, focal spot size and sample positioning. Presented here are new developments at the Extreme Conditions beamline (P02.2, PETRA III, DESY, Germany) that enable considerable improvements in data collection at very high pressures and small scattering volumes. In particular, the focusing of the X-ray beam to the sub-micrometer level is described, and control of the aberrations of the focusing compound refractive lenses is made possible with the implementation of a correcting phase plate. This device provides a significant enhancement of the signal-to-noise ratio by conditioning the beam shape profile at the focal spot. A new sample alignment system with a small sphere of confusion enables single-crystal data collection from grains of micrometer to sub-micrometer dimensions subjected to pressures as high as 200 GPa. The combination of the technical development of the optical path and the sample alignment system contributes to research and gives benefits on various levels, including rapid and accurate diffraction mapping of samples with sub-micrometer resolution at multimegabar pressures.
35.	Golosova, N. O., et al. (författare) Magnetic and structural properties of FeCO3 at high pressures 2017 Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 96:13 Tidskriftsartikel (refereegranskat)abstract The structural and magnetic properties of siderite FeCO3 have been studied by means of neutron powder diffraction at pressures up to 7.5 GPa and first-principles theoretical calculations. The lattice compression in the rhombohedral calcite-type structure is dominated by the reduction of the Fe-O bonds, while the changes of the C-O bonds are much less pronounced. The Neel temperature of the antiferromagnetic ( AFM) ground state increases substantially under pressure with a coefficient dT(N)/dP = 1.8K/GPa, which is about 1.5 times larger in comparison with those predicted by the empirical Bloch rule. The ab initio calculations were performed in the framework of the density functional theory including Hubbard-U correction. The calculated structural parameters and Neel temperature as functions of pressure provide a reasonable agreement with the experimental results. The analysis of the density of electronic states points toward increased covalent bonding between the Fe and O atoms upon pressure, giving rise to unexpectedly large pressure coefficient of the Neel temperature and reduced ordered magnetic moments of Fe atoms.
36.	Isaev, Eyvas, et al. (författare) Impact of lattice vibrations on equation of state of the hardest boron phase 2011 Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 83:13, s. 132106- 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.
37.	Kantor, I., et al. (författare) Pressure-induced phase transition in Mg0.8Fe0.2O ferropericlase 2006 Ingår i: Phys. Chem. Miner.. ; 33:35 Tidskriftsartikel (refereegranskat)
38.	Kantor, I, et al. (författare) Short-range order and Fe clustering in Mg1-xFexO under high pressure 2009 Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 80:1, s. 014204- Tidskriftsartikel (refereegranskat)abstract By combining high-pressure and high-temperature Moumlssbauer spectroscopic studies of (Mg,Fe)O with results of ab initio simulations, several important properties of this material were established. Under high pressure (Mg,Fe)O shows changes in the short-range order with the tendency to form iron clusters. These changes were found to be irreversible, implying sluggish kinetics of these processes at ambient conditions. The pressure-induced spin crossover is interpreted here as a gradual noncooperative transition. The onset and width of spin crossover depends, therefore, not only on pressure, temperature, and composition, but also on short-range order in the FeO-MgO solid solution.
39.	Koemets, E., et al. (författare) Revealing the Complex Nature of Bonding in the Binary High-Pressure Compound FeO2 2021 Ingår i: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 126:10 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.
40.	Kuznetsov, A. Y., et al. (författare) High-pressure synthesis and physical properties of an orthorhombic phase of chromium dioxide 2006 Ingår i: J. Appl. Phys.. ; 5:99 Tidskriftsartikel (refereegranskat)
41.	Lazor, P, et al. (författare) Synchrotron X-ray Diffraction of Iron under High Pressure and Temperature 2000 Ingår i: Proceedings of the AIRAPT-17, Honolulu, Hawaii, July 1999. - 81 7371 339 1 ; , s. 1059-1062 Konferensbidrag (refereegranskat)
42.	Mattesini, M., et al. (författare) Cubic TiO2 as a potential light absorber in solar-energy conversion 2004 Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 70:11 Tidskriftsartikel (refereegranskat)abstract Materials are currently sought for use in the photo-induced decomposition of water on crystalline electrodes. Titanium dioxide is valuable in this respect. The electronic structural properties of cubic TiO2 polymorphs were investigated by means of first-principles methods. We demonstrate that both fluorite- and pyrite-type TiO2 have important optical absorptive transitions in the region of the visible light. A cubic TiO2 phase that can efficiently absorb the sunlight would be an important candidate material for the development of the solar cells. Also, we present results on the Ti L edges for the two different titania forms. We predict that a qualitative spectroscopic discrimination of the cubic polymorphs can be achieved by following the Ti 2p → 3d x-ray transitions.
43.	Mattesini, M., et al. (författare) Cubic TiO2 as a potential light absorber in solar-energy conversion 2004 Ingår i: Phys. Rev. B. ; 70, s. 115101- Tidskriftsartikel (refereegranskat)
44.	Mattesini, M., et al. (författare) High-pressure and high-temperature synthesis of the cubic TiO2 polymorph 2004 Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 70, s. 212101- Tidskriftsartikel (refereegranskat)
45.	Mikhaylushkin, Arkady, 1977-, et al. (författare) Iron compressed and heated to extreme conditions 2008 Ingår i: American Physical Society March Meeting 2008,2008. Konferensbidrag (refereegranskat)
46.	Mikhaylushkin, Arkady, 1977-, et al. (författare) Pure iron compressed and heated to extreme conditions 2007 Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 99, s. 165505-1-165505-4 Tidskriftsartikel (refereegranskat)
47.	Norrby, Niklas, et al. (författare) High pressure and high temperature stabilization of cubic AlN in Ti0.60Al0.40N 2013 Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 113:5 Tidskriftsartikel (refereegranskat)abstract In the present work, the decomposition of unstable arc evaporated Ti0.6Al0.4N at elevated temperatures and quasihydrostatic pressures has been studied both experimentally and by first-principles calculations. High pressure and high temperature (HPHT) treatment of the samples was realized using the multi anvil press and diamond anvil cell techniques. The products of the HPHT treatment of Ti0.6Al0.4N were investigated using x-ray diffractometry and transmission electron microscopy. Complimentary calculations show that both hydrostatic pressure and high temperature stabilize the cubic phase of AlN, which is one of the decomposition products of Ti0.6Al0.4N. This is in agreement with the experimental results which in addition suggest that the presence of Ti in the system serves to increase the stability region of the cubic c-AlN phase. The results are industrially important as they show that Ti0.6Al0.4N coatings on cutting inserts do not deteriorate faster under pressure due to the cubic AlN to hexagonal AlN transformation.
48.	Ponomareva, A. V., et al. (författare) Influence of global magnetic state on chemical interactions in high-pressure high-temperature synthesis of B2 Fe2Si 2009 Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 94:18 Tidskriftsartikel (refereegranskat)abstract We show that effective chemical interactions in an alloy can be tuned by its global magnetic state, which opens exciting possibilities for materials synthesis. Using first-principles theory we demonstrate that at pressure of 20 GPa and at high temperatures, the effective chemical interactions in paramagnetic Fe-Si system are strongly influenced by the magnetic disorder favoring a formation of cubic Fe2Si phase with B2 structure, which is not present in the alloy phase diagram. Our experiments confirm theoretical predictions, and the B2 Fe2Si alloy is synthesized from Fe-Si mixture using multianvil press.
49.	Potapkin, V., et al. (författare) Magnetic interactions in NiO at ultrahigh pressure 2016 Ingår i: PHYSICAL REVIEW B. - : AMER PHYSICAL SOC. - 2469-9950. ; 93:20, s. 201110- Tidskriftsartikel (refereegranskat)abstract Magnetic properties of NiO have been studied in the multimegabar pressure range by nuclear forward scattering of synchrotron radiation using the 67.4 keV Mossbauer transition of Ni-61. The observed magnetic hyperfine splitting confirms the antiferromagnetic state of NiO up to 280 GPa, the highest pressure where magnetism has been observed so far, in any material. Remarkably, the hyperfine field increases from 8.47 T at ambient pressure to similar to 24 T at the highest pressure, ruling out the possibility of a magnetic collapse. A joint x-ray diffraction and extended x-ray-absorption fine structure investigation reveals that NiO remains in a distorted sodium chloride structure in the entire studied pressure range. Ab initio calculations support the experimental observations, and further indicate a complete absence of Mott transition in NiO up to at least 280 GPa.
50.	Rekhi, S., et al. (författare) Experimental and theoretical investigations on eskolaite (Cr2O3) at high pressures 2000 Ingår i: Journal of Alloys and Compounds. - 0925-8388 .- 1873-4669. ; 302:02-jan, s. 16-20 Tidskriftsartikel (refereegranskat)

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