Actinide elements produce a plethora of interesting physical behaviors due to the $5f$ states. This review compiles and analyzes progress in the understanding of the electronic and magnetic structure of the $5f$ states in actinide metals. Particular interest is given to electron energy-loss spectroscopy and many-electron atomic spectral calculations, since there is now an appreciable library of core $d\ensuremath{\rightarrow}\text{valence}$ $f$ transitions for Th, U, Np, Pu, Am, and Cm. These results are interwoven and discussed against published experimental data, such as x-ray photoemission and absorption spectroscopy, transport measurements, and electron, x-ray, and neutron diffraction, as well as theoretical results, such as density-functional theory and dynamical mean-field theory.

Nature of the 5f states in actinide metals

The elastic constants c11, c12 and c44 of U, Np, Pu, and Am telluride single crystals have been obtained by Brillouin scattering from the measured sound velocities in prominent crystallographic directions. In case of the U chalcogenides also by ultrasound techniques. The Cauchy pressure, the Poisson ratio, the anisotropy ratio, the bulk modulus and the Debye temperature have been derived from these data. U and Pu telluride have a negative c12, implying intermediate valence. AmTe has a very low bulk modulus, but a positive c12. It is extremely soft, with a very low sound velocity. For AmTe also the LO and TO phonon frequencies could be determined. The elastic data point to a divalent Am state. The optical reflectivity of the light actinide tellurides (and sometimes of all chalcogenides) has been measured between UV and infrared wavelengths, in the case of AmTe down to the far infrared. The plasma edge of the free carriers has been determined, which yields the ratio of n/m*. Together with the γ value of the specific heat and magnetic data a consistent proposal for the electronic structure of the light actinide chalcogenides can be given. Thus, the Pu chalcogenides are intermediate valent and represent the high-pressure phase of the corresponding Sm chalcogenides. AmTe, as judged by the electronic, optic and magnetic properties seems to be in the 5f7 configuration, i.e. divalent Am, but with a narrow, half-filled (24 meV) wide 5f band, about 0.1 eV below the bottom of the 6d conduction band. We thus propose a new kind of unhybridized heavy fermion. Also AmTe seems to represent a high-pressure phase of EuTe.

Electronic and elastic properties of the light actinide tellurides

Publisher Summary Stimulated by technological prospects of high-density magneto-optical (MO) recording and by fundamental research on magnetism, a wealth of experimental data on MO Kerr spectra had been collected until the beginning of the nineties. The theoretical explanation of magneto-optical Kerr effect (MOKE) spectra because of first-principles band-structure calculations was at that time in its infancy, and consequently all the insight that theory could give in the microscopic mechanism leading to large Kerr rotations was mainly speculative, because nothing could be proven by first-principles calculations. This situation has profoundly changed, due to the rapid development of first-principles computational research on MO Kerr spectra during the nineties.

Chapter 3 Magneto-optical kerr spectra

Pressure induced structural phase transformation and mechanical properties of NaCl-type (B1) to CsCl-type (B2) structure in uranium monochalcogenides (UX; X = S, Se, and Te) are presented. An effective interionic interaction potential is constructed, consisting of the long-range Coulomb and the Hafemeister and Flygare type short-range overlap repulsion extended up to the second-neighbour ions and the van der Waals (vdW) interaction. Particular attention is devoted to evaluate the vdW coefficients following the Slater–Kirkwood variational method, as both the ions are polarizable. Our calculated results have revealed reasonably good agreement with the available experimental data on the phase transition pressures (Pt = 81, 21, 13 GPa) and the elastic properties of UX (X = S, Se, and Te). The equation of state curves (plotted between V (P)/V (0) and pressure) for both the NaCl-type (B1) and CsCl-type (B2) structures obtained by us are in fairly good agreement with the experimental results. The calculated values of the volume collapses (ΔV (P)/V (0)) are also closer to their observed data. The variations of the second- and third-order elastic constants with pressure have followed systematic trends, which are almost identical to those exhibited by the measured and observed data in other compounds of the NaCl-type structure family.

https://iopscience.iop.org/article/10.1088/0953-8984/19/23/236204/pdf

B1–B2 structural phase transition and elastic properties of UX (X = S, Se, and Te) compounds at high pressure

The calculated electronic structure and charge density of UC and US are reported. We also report calculations on the elastic constants of the cubic compounds UC, US, and UTe using the local-spin-density approximation (LSDA) to the exchange and correlation potential. Good agreement between calculations and experiment has been obtained for UC and US suggesting that the chemical bonding is well reproduced by LSDA for these two compounds. In contrast, for UTe the calculations do not reproduce the measured negative Poissons ratio (negative ${\mathit{C}}_{12}$). We suggest that the failure to describe the elasticity of UTe reflects the weakness of LSDA in describing accurately electron systems that are strongly correlated and we speculate that UTe is an anomalous, possibly mixed valent, system.

Calculation of elastic constants in uc, us, and ute

Low-temperature resistance measurements were performed on UTe crystals in the pressure range from 1 GPa to 20 GPa The Curie temperature obtained as the maximum in the temperature derivative dR/dT, increases strongly with pressure It has a maximum at 75 GPa followed by a decrease with a smaller slope at higher pressures Another anomaly in the R-T characteristic is observed above 10 GPa and ascribed to the presence of the B2 phase, which is known to form in a very sluggish phase transformation

http://iopscience.iop.org/article/10.1088/0953-8984/4/25/011/pdf

High-pressure resistance study of UTe

Resistivity and superconductivity of americium metal under pressure up to 25 GPa

The electrical resistance of PuSb under high pressure

The electrical resistance of USe was measured between 2 and 300 K at pressures up to 20 GPa. The Curie temperature, as inferred from the maxima in the temperature derivative of the resistance, d R d T , increased strongly to a maximum at 4 GPa. At pressures above 12 GPa no indication of magnetic ordering could be found in the resistance behaviour. Comparison with previously published results on UTe is made.

The electrical resistance of USe under high pressure

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High-pressure resistance study of UTe

Resistivity and superconductivity of americium metal under pressure up to 25 GPa

The electrical resistance of PuSb under high pressure

The electrical resistance of USe under high pressure