Local structure and vibrational properties of {alpha}-Pu, {alpha}-U, and the {alpha}-U charge-density wave

Journal Article · Sun May 01 00:00:00 EDT 2005 · Physical Review. B, Condensed Matter and Materials Physics

DOI:https://doi.org/10.1103/PhysRevB.71.184113· OSTI ID:20719003

Nelson, E J; Blobaum, K J.M.; Wall, M A ^[1]; Allen, P G ^[2]; Booth, C H ^[3]

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1. Materials Science and Technology Division, Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551 (United States)
2. Chemistry and Chemical Engineering Division, Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551 (United States)
3. Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

The local atomic environment and vibrational properties of atoms in monoclinic pure {alpha}-plutonium as well as orthorhombic pure {alpha}-uranium and its low-temperature charge-density-wave (CDW) modulation are examined by extended x-ray absorption fine structure spectroscopy (EXAFS). Pu L{sub III}-edge and U L{sub III}-edge EXAFS data measured at low temperatures verify the crystal structures of {alpha}-U and {alpha}-Pu samples previously determined by x-ray diffraction and neutron scattering. Debye-Waller factors from temperature-dependent EXAFS measurements are fit with a correlated Debye model. The observed Pu-Pu bond correlated Debye temperature of {theta}{sub cD}({alpha}-Pu)=162{+-}5 K for the pure {alpha}-Pu phase agrees with our previous measurement of the correlated Debye temperature of the gallium-containing {alpha}{sup '}-Pu phase in a mixed phase 1.9 at. % Ga-doped {alpha}{sup '}-Pu/{delta}-Pu alloy. The temperature dependence of the U-U nearest neighbor Debye-Waller factor exhibits a sharp discontinuity in slope near T{sub CDW}=43 K, the transition temperature at which the charge-density wave (CDW) in {alpha}-U condenses from a soft phonon mode along the (100) direction. Our measurement of the CDW using EXAFS is the first observation of the structure of the CDW in polycrystalline {alpha}-U. The different temperature dependence of the Debye-Waller factor for T<T{sub CDW} can be modeled by the change in bond length distributions resulting from condensation of the charge density wave. For T>T{sub CDW}, the observed correlated Debye temperature of {theta}{sub cD}({alpha}-U)=199{+-}3 K is in good agreement with other measurements of the Debye temperature for polycrystalline {alpha}-U. CDW structural models fit to the {alpha}-U EXAFS data support a squared CDW at the lowest temperatures, with a displacement amplitude of {epsilon}=0.05{+-}0.02 A.

• OSTI ID: 20719003
• Journal Information: Physical Review. B, Condensed Matter and Materials Physics, Vol. 71, Issue 18; Other Information: DOI: 10.1103/PhysRevB.71.184113; (c) 2005 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1098-0121
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ABSORPTION SPECTROSCOPY
BOND LENGTHS
CHARGE DENSITY
DEBYE TEMPERATURE
DEBYE-WALLER FACTOR
DOPED MATERIALS
FINE STRUCTURE
GALLIUM
MONOCLINIC LATTICES
NEUTRON DIFFRACTION
PHONONS
PLUTONIUM-ALPHA
PLUTONIUM-DELTA
POLYCRYSTALS
TEMPERATURE DEPENDENCE
TRANSITION TEMPERATURE
URANIUM-ALPHA
X-RAY DIFFRACTION
X-RAY SPECTROSCOPY