J. Rebizant

Plutonium-based superconductivity with a transition temperature above 18 K

Plutonium is a metal of both technological relevance and fundamental scientific interest. Nevertheless, the electronic structure of plutonium, which directly influences its metallurgical properties, is poorly understood. For example, plutoniums 5f electrons are poised on the border between localized and itinerant, and their theoretical treatment pushes the limits of current electronic structure calculations. Here we extend the range of complexity exhibited by plutonium with the discovery of superconductivity in PuCoGa5. We argue that the observed superconductivity results directly from plutoniums anomalous electronic properties and as such serves as a bridge between two classes of spin-fluctuation-mediated superconductors: the known heavy-fermion superconductors and the high-Tc copper oxides. We suggest that the mechanism of superconductivity is unconventional; seen in that context, the fact that the transition temperature, Tc ≈ 18.5 K, is an order of magnitude greater than the maximum seen in the U- and Ce-based heavy-fermion systems may be natural. The large critical current displayed by PuCoGa5, which comes from radiation-induced self damage that creates pinning centres, would be of technological importance for applied superconductivity if the hazardous material plutonium were not a constituent.

Electroseparation of Actinides from Lanthanides on Solid Aluminum Electrode in LiCl-KCl Eutectic Melts

University of Grenoble, ENSEEG, 38402 Saint Martin d’He`res, FranceThis work presents a study on the electrochemical behavior of actinides (An 5 Am and Pu! and lanthanides (Ln 5 La and Nd!onto solid aluminum cathodes in a molten LiCl-KCl eutectic at 733 K. Cyclic voltammetry of these elements onto Al workingelectrode is carried out to estimate the reduction potentials of An and Ln and to predict the efficiency of an An/Ln separation byelectrolysis. Results show that the reduction of Am

Advances in the preparation and characterization of transuranium systems

The most remarkable advance that one can report as regards transuranium systems is certainly the discovery of superconductivity above 18 K in PuCoGa5. Motivated by this discovery, we have investigated bulk samples of both PuCoGa5 and its Rh analogue. Characterizations of polycrystalline Co and Rh compounds are reported. The new PuRhGa5 compound is also found to become superconducting above 8 K.

Triple-q Octupolar Ordering in NpO2.

We report the results of resonant x-ray scattering experiments performed at the Np M(4,5) edges in NpO2. Below T(0)=25 K, the development of long-range order of Np electric quadrupoles is revealed by the growth of superlattice Bragg peaks. The polarization and azimuthal dependence of the intensity of the resonant peaks are well reproduced assuming anisotropic tensor susceptibility scattering from a triple-q(-->) longitudinal antiferroquadrupolar structure. Electric-quadrupole order in NpO2 could be driven by the ordering at T0 of magnetic octupoles of Gamma(5) symmetry, splitting the Np ground state quartet and leading to a singlet ground state with zero dipole-magnetic moment.

A new family of actinide ternary intermetallic compounds

Abstract We have prepared an extended group of compounds of the general formula An 2 T 2 X (AnU, Np; T Ni, Co, Rh, Pd, Pt, Ir; XIn, Sn), which crystallize in the tetragonal structure (U 3 Si 2 type). The lattice parameters and atomic positions were determined using X-ray diffraction on single crystals. Preliminary magnetic and Mossbauer spectroscopy data show that we can follow the onset of magnetism within this group, which can be correlated with the Hill criterion and the development of 5f-d hybridization.

Direct observation of electric-quadrupolar order in UO2

We report direct experimental evidence for long-range antiferro ordering of the electricquadrupole moments on the U ions. Resonant x-ray scattering experiments at the uranium M4 absorption edge show a characteristic dependence in the integrated intensity upon rotation of the crystal around the scattering vector. Although quadrupolar order in uranium dioxide was advocated already in the 1960s no experimental evidence for this phenomenon was provided until now. We conclude with a possible model to explain the phase diagram of the solid solutions of UO2 and NpO2. We suggest that in the region 0.30 < x < 0.75 neither the transverse nor the longitudinal quadrupole ordering can dominate, leading to frustration and only short-range ordering.

Preparation and photoelectron spectroscopy study of UNx thin films

Abstract Thin films of UN and U 2 N 3 were prepared by reactive DC sputtering of U in N 2 -containing atmosphere. The composition of the films was modified by varying the partial pressure of N 2 . 4f-Core-level photoelectron spectra as well as valence-band spectra obtained with HeII and HeI photoexcitation confirm the itinerant character of the 5f-electronic states in UN, showing a high density of states at the Fermi energy. The 4f peaks in U 2 N 3 are shifted towards higher binding energy and are symmetric, indicating a low density of states at the Fermi level. Valence-band spectra show indeed a maximum of 5f emission at 0.8 eV below the Fermi level, but some 5f intensity at the Fermi level is preserved, contradicting full 5f localisation.

Metallorganische Chemie des Technetiums: VIII. Technetium(I)-carbonyl-Komplexe mit Polypyrazol-1-yl-borato-Liganden im Vergleich mit seinen Mn- und Re-Homologen

Abstract The compounds HB(C3H3N2)3Tc(CO)3 and HB(3,5-Me2C3HN2)3Tc(CO)3 have been synthesized for the first time, and their molecular and crystal structure as well as the structures of the known analogous compounds of manganese and rhenium determined by single-crystal X-ray diffraction. The IR-, 1H-NMR-, 13C-NMR-, UV- and EI-MS-spectroscopic data are discussed in correlation to the electric dipole moment and the charge distribution within the molecule.

Heavy fermion behavior of U2T2X compounds

Magnetic and specific-heat studies of U[sub 2][ital T][sub 2][ital X] compounds show a frequent occurrence of the [gamma] enhancement in conjunction with the onset of antiferromagnetic ordering. The largest value of 830 mJ/mol K[sup 2] was observed in U[sub 2]Pt[sub 2]In, which is nonmagnetic down to 1.2 K. Variations of electronic structure are documented by optimized relativistic LCAO calculation.Magnetic and specific‐heat studies of U2T2X compounds show a frequent occurrence of the γ enhancement in conjunction with the onset of antiferromagnetic ordering. The largest value of 830 mJ/mol K2 was observed in U2Pt2In, which is nonmagnetic down to 1.2 K. Variations of electronic structure are documented by optimized relativistic LCAO calculation.

The first cationic indenyl-f-metal complexes with pentagonal bipyramidal geometry. Crystal structures of [C9H7UBr2(CH3CN)4]+2 [UBr6]2− and [{C9H7UBr(CH3CN)4}2O]2+ [UBr62−☆

Abstract Treatment of the octahedral complexes, C9H7AnHal3·2C4H8O (An = U r Th) with verypure methyl cyanide leads to the formation of the novel complexes [C9H7AnHal2(CH3CN)4]+2 [AnHal62− (I). Reaction of C9H7UHal3·2C4H8O with methyl cyanide containing dry oxygen gives the red complex [{C9H7UHal-(CH3CN)4}2O]2+ [UHal6]2− (II). Both uranium complexes with Hal = Br have been characterized by elemental analysis, vibration spectroscopy and X-ray structure analysis. The cation in I exhibits a pentagonal bipyramidal geometry and that in II consists of two pentagonal bipyrmids bonded by an oxygen occupying the common apex. A series of analogous compounds containing the 1-ethylindenyl, 1, 4, 7-trimethylindenyl or 1,2,3,4,5,6,7-heptamethylindenyl anion has been prepared and characterized . The reactions of the octahedral compounds with butyronitirle and benzonitrile is discussed.