Electronic structure and phase stability of Pu-Ga alloys

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Plutonium metal has six different crystallographic allotropes from room temperature until it melts just above 600 C. The room-temperature {alpha} phase is monoclinic with 32 atoms per unit cell, (an {alpha} phase with 16 atoms per cell also exists), which is the lowest-symmetry crystal structure known of any pure element. In fact, only the high-temperature {delta} (fcc) phase of Pu possesses one of the traditional close-packed structures. The low-symmetry and small lattice constants of the lowest-temperature phase of the light actinides can be used as an argument for f-bonding in these materials. The large volume increase in Pu in going ... continued below

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8 pages; Other: FDE: PDF

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Gonis, A., LLNL March 1, 1997.

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Description

Plutonium metal has six different crystallographic allotropes from room temperature until it melts just above 600 C. The room-temperature {alpha} phase is monoclinic with 32 atoms per unit cell, (an {alpha} phase with 16 atoms per cell also exists), which is the lowest-symmetry crystal structure known of any pure element. In fact, only the high-temperature {delta} (fcc) phase of Pu possesses one of the traditional close-packed structures. The low-symmetry and small lattice constants of the lowest-temperature phase of the light actinides can be used as an argument for f-bonding in these materials. The large volume increase in Pu in going from the {alpha} to the {delta} phase has been argued on phenomenological grounds to be the result of decreased f-bonding. In addition, XPS data have been obtained for both the {alpha} and the {delta} phases. Both sets of data show the presence of a peak below the Fermi level (EF). This peak is 2.0 eV wide in the {alpha} phase and 3.0 eV wide in the {delta} phase. The XPS intensity calculations (for the two phases) which treat the f-electrons as bonding states agree with the measurements of the {alpha} phase spectra, but not with those of the {delta} phase. The calculated spectrum shows a narrow f-peak pinned at EF instead of the wide f-peak below E{sub F} seen in the XPS spectra. It can be argued that the wide spectra seen experimentally are due to the multiplet structure of localized f-states that do not participate very actively in the bonding. In spite of the difference in the properties of the {alpha} and {delta} phases of Pu (for example {alpha}-Pu is brittle while {delta}-Pu is ductile), it is not difficult to retain either phase by alloying. Indeed, it is often desirable to retain the ductile {delta} phase for engineering purposes, by alloying for example, Pu with Al, Ga, or Si.

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8 pages; Other: FDE: PDF

Notes

OSTI as DE00016380

Source

  • Topical Conference on Plutonium and the Actinides, Santa Fe, NM (US), 08/24/1997--08/27/1997; Other Information: Supercedes report DE98050999; PBD: 01 Mar 97

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  • Other: DE98050999
  • Report No.: UCRL-JC-127364
  • Report No.: CONF-970844*--
  • Grant Number: W-7405-Eng-48
  • Office of Scientific & Technical Information Report Number: 16380
  • Archival Resource Key: ark:/67531/metadc618819

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  • March 1, 1997

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  • June 16, 2015, 7:43 a.m.

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  • Jan. 3, 2017, 12:22 p.m.

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Gonis, A., LLNL. Electronic structure and phase stability of Pu-Ga alloys, article, March 1, 1997; (digital.library.unt.edu/ark:/67531/metadc618819/: accessed October 23, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.