Crystallographic phase transitions in actinide metals as a function of pressure

Conference · Wed Sep 01 00:00:00 EDT 1993

OSTI ID:10181505

Eriksson, O; Soederlind, P; Melsen, J; Ahuja, R; Johansson, B ^[1]; Wills, J M; Boring, A M ^[2]

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1. Uppsala Univ. (Sweden). Dept. of Physics
2. Los Alamos National Lab., NM (United States)

We present first-principles calculations of the equilibrium volumes and crystal structures of the light actinides (Th--Pu). The calculated equilibrium volumes for fcc Th, bct Pu, {alpha}-U, and {beta}-Np are found to agree reasonably well with the experimental data, and when comparing the total energies of the bcc, fcc, bct, {alpha}-U, and {beta}-Np structures we obtain the correct crystal structures for all studied systems. Equilibrium volumes for Th--Pu, using a hypothetical fcc structure, have been calculated; although spin-orbit coupling is included in these calculations, the calculated equilibrium volume of Pu is smaller than for Np, in disagreement with experiment. Moreover, the calculated tetragonal elastic constant, C{prime}, is shown to be negative for bcc U, bcc Np, bcc Pu, and fcc Pu. Thus, our zero temperature calculations suggest that the bcc structure is unstable for these elements and that fcc Pu is also unstable. This is in conflict with experiment and we are led to the conclusion that temperature effects must be of crucial importance for stabilizing cubic structures in U, Np, and Pu. Further, as a function of decreasing volume we predict a crystal structure sequence fcc {yields} bct {yields} fcc in Th, a sequence {alpha}-U {yields} bct {yields} bcc in U, and a sequence {beta}-Np {yields} bct {yields} bcc in Np. Also, a sequence of transitions in Sc as a function of decreasing volume have been calculated, namely hcp {yields} fcc {yields} {omega} {yields} {beta}-Np {yields} bcc.

• Research Organization: Los Alamos National Lab., NM (United States)
• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: W-7405-ENG-36
• OSTI ID: 10181505
• Report Number(s): LA-UR-93-3086; CONF-930905-2; ON: DE93040138; TRN: 93:021709
• Resource Relation: Conference: Actinides `93,Santa Fe, NM (United States),19-24 Sep 1993; Other Information: PBD: [1993]
• Country of Publication: United States
• Language: English

Related Subjects

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
36 MATERIALS SCIENCE
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
NEPTUNIUM
CRYSTAL-PHASE TRANSFORMATIONS
THORIUM
URANIUM
PLUTONIUM
ACTINIDES
SCANDIUM
FCC LATTICES
BCC LATTICES
HCP LATTICES
CRYSTAL STRUCTURE
VOLUME
400702
360102
050700
PROPERTIES OF RADIOACTIVE MATERIALS
STRUCTURE AND PHASE STUDIES
FUELS PRODUCTION AND PROPERTIES