107 research outputs found
Photoelectron spectroscopy of NpPd3 and PuPd3
We present the results of x-ray and ultraviolet photoelectron spectroscopy of NpPd3 and PuPd3. The spectra indicate that for both compounds, the 5f electrons are well localized on the actinide sites. Comparison with bulk measurements indicates that for NpPd3 the electrons have a valence of Np3+ and thus a ground state 5f4 with a Hund's rules 5I4 configuration. Similarly for PuPd3, we find a Pu3+ valence, 5f5 ground state and a Hund's rules 6H5/2 configuration
Electronic structure and non-magnetic character of -Pu-Am alloys
The {\em around-mean-field} LSDA+U correlated band theory is applied to
investigate the electronic and magnetic structure of -Pu-Am alloys.
Despite a lattice expansion caused by the Am atoms, neither tendency to 5
localization nor formation of local magnetic moments on Pu atoms in Pu-Am
alloys are found. The -manifolds in the alloys are calculated being very
similar to a simple weighted superposition of elemental Pu and Am -states
A Full-Potential-Linearized-Augmented-Plane-Wave Electronic Structure Study of delta-Plutonium and the (001) Surface
The electronic and geometric properties of bulk fcc delta-plutonium and the
quantum size effects in the surface energies and the work functions of the
(001) ultra thin films (UTF) up to 7 layers have been investigated with
periodic density functional theory calculations within the full-potential
linearized augmented-plane wave (FP-LAPW) approach as implemented in the WIEN2k
package. Our calculated equilibrium atomic volume of 178.3 a.u.^3 and bulk
modulus of 24.9 GPa at the fully relativistic level of theory, i.e.
spin-polarization and spin-orbit coupling included, are in good agreement with
the experimental values of 168.2 a.u.^3 and 25 GPa (593 K), respectively. The
calculated equilibrium lattice constants at different levels of approximation
are used in the surface properties calculations for the thin films. The surface
energy is found to be rapidly converged with the semi-infinite surface energy
predicted to be 0.692eV at the fully-relativistic level.Comment: 27 pages,8 figure
Measurements of the band gap of ThF4 by electron spectroscopy techniques
We present an experimental determination of the band gap of ThF4 performed by two different techniques.
The first measurement was performed by combining x-ray photoemission spectroscopy and bremsstrahlung
isochromat spectroscopy. The second measurement exploited the position of the inelastic threshold in reflection
electron energy loss spectroscopy. Both measurements gave compatible values of the band gap, with the average
E = 10.2(2) eV. This value was found to be in excellent agreement with theoretical calculations. The measured
band gap is significantly larger than the 229mTh excitation energy, making ThF4 a possible candidate material for
a solid-state nuclear clock based on the vacuum ultraviolet \u3b3 decay
Multiplet effects in the electronic structure of -Pu, Am and their compounds
We propose a straightforward and efficient procedure to perform dynamical
mean-field (DMFT) calculations on the top of the static mean-field LDA+U
approximation. Starting from self-consistent LDA+U ground state we included
multiplet transitions using the Hubbard-I approximation, which yields a very
good agreement with experimental photoelectron spectra of -Pu, Am, and
their selected compounds.Comment: submitted to Europhysics Letter
Nature of non-magnetic strongly-correlated state in delta-plutonium
Ab-initio relativistic dynamical mean-field theory is applied to resolve the
long-standing controversy between theory and experiment in the "simple"
face-centered cubic phase of plutonium called delta-Pu. In agreement with
experiment, neither static nor dynamical magnetic moments are predicted. In
addition, the quasiparticle density of states reproduces not only the peak
close to the Fermi level, which explains the large coefficient of electronic
specific heat, but also main 5f features observed in photoelectron
spectroscopy.Comment: 9 pages, 3 figure
Crystal chemical design, synthesis and characterisation of U(IV)-dominant betafite phases for actinide immobilisation
Crystal chemical design principles were applied to synthesise novel U4+ dominant and titanium excess betafite phases
Ca1.15(5)U0.56(4)Zr0.17(2)Ti2.19(2)O7 and Ca1.10(4)U0.68(4)Zr0.15(3)Ti2.12(2)O7, in high yield (85–95 wt%), and ceramic density reaching 99% of theoretical. Substitution of Ti on the A-site of the pyrochlore structure, in excess of full B-site occupancy, enabled the radius ratio (rA/rB = 1.69) to be tuned into the pyrochlore stability field, approximately 1.48 ≲ rA/rB ≲ 1.78, in contrast to the archetype composition CaUTi2O7 (rA/rB = 1.75). U L3-edge XANES and U 4f7/2 and U 4f5/2 XPS data evidenced U4+ as the dominant speciation, consistent with the determined chemical compositions. The new betafite phases, and further analysis reported herein, point to a wider family of actinide betafite pyrochlores that could be stabilised by application of the underlying crystal chemical principle applied here
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