Understanding Materials Under High Pressure

JULY 12, 2007

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A schematic representation of the shell structure of Sn under pressure from a fanciful drawing of a diamond-anvil cell. (Schematic available at webelements.com.)

The ability to reliably predict the bonding and interatomic forces in solids is an important topic in condensed-matter physics, and various theoretical methods have been developed and are constantly refined. For basic as well as applied science, the power of prediction provides fundamental insights into materials and paves the road to new and potentially important technologies. The atomic vibrations in a material are particularly sensitive to the bonding, and, in comparison with experiments, can provide a serious test for any theoretical description. This goal has been met by the Argonne Advanced Photon Source (APS) that reveals, for the first time, the vibrational density of states of Sn (tin) at high pressure up to 64 GPa and their accurate modeling with density functional theory calculations. (Density of states, or DOS, is the property in condensed-matter physics that quantifies how closely packed energy levels are in a physical system.)

In carrying out this research, scientists from the University of Nevada, Las Vegas; Los Alamos National Laboratory; East China Normal University; Wilbur Wright College; and Argonne, using the X-ray Operations and Research beamline 3-ID at the APS, have achieved remarkable agreement between measurement and theory at different very high pressures. As this is far from the common situation, it constitutes a major advance in high-pressure materials research.

Based on the DOS results, the group derived several thermodynamic quantities that are important to a fundamentally improved understanding of Sn and similar metals under extreme pressures. The established excellent agreement between theory and measurement for Sn, even at the very small excitation energies of atomic vibrations, renews our hope for the validity of theoretical methods for compounds at extremely high pressures.

Contact: Hubertus Giefers hubertus@physics.unlv.edu

See: Hubertus Giefers, Elizabeth A. Tanis, Sven P. Rudin, Carl Greeff, Xuezhi Ke, Changfeng Chen, Malcolm F. Nicol, Michael Pravica, Walter Pravica, Jiyong Zhao, Ahmet Alatas, Michael Lerche, Wolfgang Sturhahn, and Ercan Alp, “ Phonon Density of States of Metallic Sn at High Pressure,” Phys. Rev. Lett. 98, 245502 (2007). DOI: 10.1103/PhysRevLett.98.245502

Support for this research was provided by the U.S. Department of Energy Cooperative Agreement No. DEFC52-06NA26274 with the University of Nevada, Las Vegas. S. P. R. and C. G. are supported by the Department of Energy under Contract No.W-7405-Eng-36. Use of the Advanced Photon Source is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

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