Yu Jiang

Multiconfigurational nature of 5f orbitals in uranium and plutonium intermetallics

Uranium and plutonium’s 5f electrons are tenuously poised between strongly bonding with ligand spd-states and residing close to the nucleus. The unusual properties of these elements and their compounds (e.g., the six different allotropes of elemental plutonium) are widely believed to depend on the related attributes of f-orbital occupancy and delocalization for which a quantitative measure is lacking. By employing resonant X-ray emission spectroscopy (RXES) and X-ray absorption near-edge structure (XANES) spectroscopy and making comparisons to specific heat measurements, we demonstrate the presence of multiconfigurational f-orbital states in the actinide elements U and Pu and in a wide range of uranium and plutonium intermetallic compounds. These results provide a robust experimental basis for a new framework toward understanding the strongly-correlated behavior of actinide materials.

Local Structure of La1 xSrxCoO3 Determined from EXAFS and Neutron Pair Distribution Function Studies

The combined local structure techniques, extended x-ray absorption fine structure and neutron pair distribution function analysis, have been used for temperatures 4< or =T< or =330 K to rule out a large Jahn-Teller (JT) distortion of the Co-O bond in La1-xSrxCoO3 for a significant fraction of Co sites (x< or =0.35), indicating few, if any, JT-active, singly occupied e_{g} Co sites exist.The combined local structure techniques, extended x-ray absorption fine structure and neutron pair distribution function analysis, have been used for temperatures 4 {le} T {le} 330 K to rule out a large Jahn-Teller (JT) distortion of the Co-O bond in La{sub 1-x}Sr{sub x}CoO{sub 3} for a significant fraction of Co sites (x {le} 0.35), indicating few, if any, JT-active, singly occupied e{sub g} Co sites exist.

Self-irradiation damage to the local structure of plutonium and plutonium intermetallics

The effect of self-irradiation damage on the local structure of δ-Pu, PuAl2, PuGa3, and other Pu intermetallics has been determined for samples stored at room temperature using the extended x-ray absorption fine-structure (EXAFS) technique. These measurements indicate that the intermetallic samples damage at a similar rate as indicated in previous studies of PuCoGa5. In contrast, δ-Pu data indicate a much slower damage accumulation rate. To explore the effect of storage temperature and possible room temperature annealing effects, we also collected EXAFS data on a δ-Pu sample that was held at less than 32u2009K for a two month period. This sample damaged much more quickly. In addition, the measurable damage was annealed out at above only 135u2009K. Data from samples of δ-Pu with different Ga concentrations and results on all samples collected from different absorption edges are also reported. These results are discussed in terms of the vibrational properties of the materials and the role of Ga in δ-Pu as a network...

Synthesis, structure and physical properties of YbNi3Al9.23.

The physical properties of YbNi(3)Al(9.23(1)), including the crystal structure, magnetization, specific heat, valence, and electrical resistivity, are reported. Single crystal x-ray diffraction reveals that the compound crystallizes with the rhombohedral space group R32 and has unit cell parameters a = 7.2443(3) Å and c = 27.251(3) Å with some crystallographic disorder at Al sites. The compound orders antiferromagnetically at T(N) = 3 K despite the presence of strong ferromagnetic correlations, accompanied by a spin-flop-like transition to a moment-aligned state above 0.1 T. X-ray absorption spectroscopy and magnetic susceptibility measurements indicate a localized Yb(3+) electronic configuration, while the Sommerfeld coefficient for the magnetically ordered state was determined as approximately 135 mJ mol(-1) K(-2), suggesting moderately heavy fermion behavior. Therefore, these data indicate a balance between competing Ruderman-Kittel-Kasuya-Yosida (RKKY) and Kondo interactions in YbNi(3)Al(9.23(1)) with a somewhat dominant RKKY interaction that leads to a relatively high ordering temperature.

PuPt2In7: a computational and experimental investigation

of 250 mJ/mol K 2 indicates heavy fermion behavior. We report the results of generalized gradient approximation (GGA)+U calculations of PuPt2In7 and as yet unsynthesized isovalent PuPt2Ga7. The strength of the c-f hybridization of PuPt2In7 is similar to the PuCoIn5 superconductor. The bare and f-weighted susceptibility within the constant-matrix-element approximation is calculated, showing a maximum along the qz direction at qx = qy = 0.5. A similar and slightly stronger maximum is also found in the structurally related heavy-fermion materials PuCoGa5 and PuCoIn5. The absence of superconductivity in PuPt2In7 is examined based on the results of our calculations.

Magnetic frustration effects in uranium intermetallics

The effect of geometrical frustration on the development of the heavy-fermion state and quantum criticality is studied in UAuCu4, UAuPt4, UAu3Ni2 samples through measurements of their magnetic susceptibility, heat capacity, and electrical resistivity. In addition, since lattice disorder can play a large role in defining magnetic properties in frustrated systems, extended X-ray absorption fine structure (EXAFS) data have also been obtained. The local structure results show a strong correlation with the magnetic properties in these samples.

Order and disorder in the local and long-range structure of the spin-glass pyrochlore, Tb2Mo2O7

To understand the origin of the spin-glass state in molybdate pyrochlores, the structure of Tb(2)Mo(2)O(7) is investigated using two techniques: the long-range lattice structure was measured using neutron powder diffraction, and local structure information was obtained from the extended x-ray absorption fine structure technique. While the long-range structure appears generally well ordered, enhanced mean-squared site displacements on the O(1) site and the lack of temperature dependence of the strongly anisotropic displacement parameters for both the Mo and O(1) sites indicate some disorder exists. Likewise, the local structure measurements indicate some Mo-Mo and Tb-O(1) nearest-neighbor disorder exists, similar to that found in the related spin-glass pyrochlore, Y(2)Mo(2)O(7). Although the freezing temperature in Tb(2)Mo(2)O(7), 25xa0K, is slightly higher than in Y(2)Mo(2)O(7), 22xa0K, the degree of local pair distance disorder is actually less in Tb(2)Mo(2)O(7). This apparent contradiction is considered in light of the interactions involved in the freezing process.

Local structure of La{sub 1-x}Sr{sub x}CoO{sub 3} determined from EXAFS and neutron PDF studies.

The combined local structure techniques, extended x-ray absorption fine structure and neutron pair distribution function analysis, have been used for temperatures 4< or =T< or =330 K to rule out a large Jahn-Teller (JT) distortion of the Co-O bond in La1-xSrxCoO3 for a significant fraction of Co sites (x< or =0.35), indicating few, if any, JT-active, singly occupied e_{g} Co sites exist.The combined local structure techniques, extended x-ray absorption fine structure and neutron pair distribution function analysis, have been used for temperatures 4 {le} T {le} 330 K to rule out a large Jahn-Teller (JT) distortion of the Co-O bond in La{sub 1-x}Sr{sub x}CoO{sub 3} for a significant fraction of Co sites (x {le} 0.35), indicating few, if any, JT-active, singly occupied e{sub g} Co sites exist.