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Nature. 2015 Sep 10;525(7568):226-9. doi: 10.1038/nature14681. Epub 2015 Aug 24.

The most incompressible metal osmium at static pressures above 750 gigapascals.

Author information

1
Bavarian Research Institute of Experimental Geochemistry and Geophysics, University of Bayreuth, D-95440 Bayreuth, Germany.
2
Laboratory of Crystallography, University of Bayreuth, D-95440 Bayreuth, Germany.
3
Center for Advanced Radiation Sources, University of Chicago, Illinois 60437 Argonne, USA.
4
Photon Sciences, Deutsches Elektronen-Synchrotron (DESY), D-22603 Hamburg, Germany.
5
European Synchrotron Radiation Facility, BP 220, Grenoble F-38043, France.
6
Swedish e-Science Research Centre (SeRC), Linköping University, SE-58183 Linköping, Sweden.
7
Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-58183 Linköping, Sweden.
8
Centre de Physique Théorique, CNRS, École Polytechnique, 91128 Palaiseau, France.
9
Radboud University, Institute for Molecules and Materials, Heyendaalseweg 135, 6525AJ Nijmegen, The Netherlands.
10
Department of Theoretical Physics and Applied Mathematics, Ural Federal University, Mira street 19, Ekaterinburg, 620002, Russia.
11
Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 USA.
12
Materials Modeling and Development Laboratory, National University of Science and Technology 'MISIS', 119049 Moscow, Russia.

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. It is also very incompressible, but its high-pressure behaviour is not well understood because it has been studied 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, 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.

PMID:
26302297
DOI:
10.1038/nature14681

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