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

Journal Article · Tue Aug 10 04:00:00 EDT 2004 · Physical Review B

OSTI ID:860901

Nelson, E J; Allen, P G; Blobaum, K J.M.; Wall, W A; Booth, C H

The local atomic environment and vibrational properties of atoms in monoclinic pure {alpha}-plutonium as well as orthorhombic pure a-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}{prime}-Pu phase in a mixed phase 1.9 at% Ga-doped {alpha}{prime}-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 {var_epsilon} = 0.05 {+-} 0.02 {angstrom}.

• Research Organization: Ernest Orlando Lawrence Berkeley NationalLaboratory, Berkeley, CA (US)
• Sponsoring Organization: USDOE Director. Office of Science. Office of Basic EnergySciences. Chemical Sciences Geosciences and Biosciences Division,Lawrence Livermore National Laboratory
• DOE Contract Number: AC02-05CH11231
• OSTI ID: 860901
• Report Number(s): LBNL--56127; UCRL-JRNL-206377; BnR: KC0302030
• Journal Information: Physical Review B, Journal Name: Physical Review B Journal Issue: 18 Vol. 71
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ABSORPTION
AMPLITUDES
ATOMS
BOND LENGTHS
CHARGE DENSITY
CRYSTAL STRUCTURE
DEBYE TEMPERATURE
DEBYE-WALLER FACTOR
FINE STRUCTURE
MODULATION
NEUTRONS
PHONONS
SCATTERING
SPECTROSCOPY
STRUCTURAL MODELS
TEMPERATURE DEPENDENCE
TRANSITION TEMPERATURE
X-RAY DIFFRACTION