Dresden 2003 – scientific programme
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SYEC: Materials under extreme conditions
SYEC 3: Extreme Conditions (Poster Session)
SYEC 3.6: Poster
Wednesday, March 26, 2003, 13:00–19:00, P2a
Sodium at megabar pressures — •M. Hanfland1, K. Syassen2, I. Loa2, N. E. Christensen3, and D. L. Novikov4 — 1ESRF, F-38043 Grenoble — 2MPI für Festkörperforschung, D-70569 Stuttgart — 3Dept. of Physics and Astronomy, Univ. of Aarhus, DK-8000 Aarhus — 4A. D. Little Inc., Acorn Park, Cambridge, MA 02140-2390
Following the prediction of symmetry-breaking phase transitions of dense Li by Neaton and Ashcroft [1], the interest in the behaviour of the light alkali metals at very high pressures has increased considerably. We have studied Na to 155 GPa pressure at 300 K using angle-dispersive x-ray diffraction with image plates as detectors. The expected transformation of Na from the bcc to the fcc structure [2,3] is observed at 65 GPa [4]. At 103 GPa Na transforms to the 16-atom cubic structure (cI16) recently found for Li at pressures above 42 GPa [5]. Two more phase transitions of Na were observed at 117 and 123 GPa, respectively. While the bcc and fcc phases show a bright metallic-like reflectivity, the phases existing beyond 100 GPa are becoming progressively darker, indicating a transition to a semimetallic state. We also report selected results of first-principles total energy calculations of the structural stability of Na at Megabar pressures and calculations of electronic properties of the observed high-pressure phases.
[1] J. B. Neaton and N. W. Ashcroft, Nature 400, 141 (1999).
[2] J. B. Neaton and N. W. Ashcroft, Phys. Rev. Lett. 86, 2830 (2001).
[3] N. E. Christensen and D. L. Novikov, Solid State Commun. 119, 477 (2001).
[4] M. Hanfland, I. Loa, K. Syassen, Phys. Rev. B 65, 184109 (2002).
[5] M. Hanfland, K. Syassen, N. E. Christensen, D. L. Novikov, Nature 408, 174 (2000).