Yu. Yu. Tsiovkin

Electronic structure and magnetic state of transuranium metals under pressure

The electronic structures of bcc Np, fcc Pu, Am, and Cm pure metals under pressure have been investigated employing the LDA + U method with spin-orbit coupling (LDA + U + SO). The magnetic state of the actinide ions was analyzed in both LS and jj coupling schemes to reveal the applicability of corresponding coupling bases. It was demonstrated that whereas Pu and Am are well described within the jj coupling scheme, Np and Cm can be described appropriately neither in a {mσ}, nor in a {jmj} basis, due to intermediate coupling scheme realization in these metals that requires some finer treatment. The LDA + U + SO results for the considered transuranium metals reveal band broadening and gradual 5f electron delocalization under pressure.

Temperature dependence of electrical resistivity in δ-plutonium alloys

The anomalous behaviour of the temperature dependence of the electrical resistivity in Pu-based dilute alloys (δ-Pu) has been considered within the Mott two-band conductivity model. It has been shown that the physical origin of the negative sign of the temperature coefficient of resistivity (TCR), observed in δ-Pu based alloys, is the interference between electron–impurity and electron–phonon interactions. A simple criterion for negative TCR observability at high temperatures (T>θD) was found and applied to explain qualitatively the experimental data on the TCR in some Pu-based dilute alloys. To make a numerical evaluation of the electrical resistivity, the coherent potential approach to the Mott two-band conductivity model was combined with the ab initio obtained fcc-Pu density of states (as the starting point in the iteration procedure) and applied to the calculation of resistivity temperature dependence in pure Pu and Pu–5 at.% Al alloy. The results are compared with experimental data.

Effect of phonon anharmonicity on the thermal and elastic properties of stabilized δ-plutonium

The Debye temperature, bulk modulus, density, and molar heat capacity of a Pu0.95Al0.05 alloy have been calculated as functions of the temperature using a self-consistent thermodynamic model developed according to a quasi-classical approach that takes into account the effect of phonon anharmonicity on the acoustic and thermodynamic properties of metals. The results of self-consistent numerical simulation of the thermal and elastic properties are compared to the available experimental data and theoretical results obtained using alternative approaches. It is established that the phonon anharmonicity plays a significant role in the formation of elastic and thermal properties of the system under consideration.

Theory of the residual resistivity of dilute alloys of nonmagnetic 3d–5d transition metals

The residual resistivity of dilute alloys of nonmagnetic transition metals is calculated by the kinetic equation method with allowance for the two-band character of the conduction at low impurity concentrations. It is shown that for all dilute nonmagnetic binary alloys of the substitution type the value of the residual resistivity is a linear function of the square modulus of the off-diagonal s-d matrix element of the scattering T-matrix.

Temperature and concentration dependences of the plutonium-americium alloy resistivity at high temperatures

A many-band model of conductivity is stated in terms of which it is shown qualitatively and quantitatively that interference scattering of conduction electrons may be the main reason for the negative temperature coefficient of resistance in actinide alloys at high temperatures (T > ΘD). The temperature run of the resistivity in such alloys is completely determined by the balance between coherent and incoherent contributions to electron-impurity-phonon scattering. The model is used to analyze the concentration and temperature dependences of the plutonium and americium alloy resistivity.

Theory of the residual electrical resistivity of binary actinide alloys

A system of self-consistent equations has been proposed for the coherent potential approximation of the multiband conductivity model for the case of conduction electron scattering from chaotic electric fields of ions of disordered binary alloy components at zero temperature. It has been qualitatively demonstrated that the deviation of the concentration dependence of the residual electrical resistivity of actinide alloys with multiband conductivity from the Nordheim rule is caused by the explicit dependence of the electrical resistivity of the alloy on the magnitude and sign of the real part of the Green’s function at the Fermi level. The derived system of equations for the multiband coherent potential approximation has been used to calculate the concentration dependence of the density of states and the residual electrical resistivity of the alloys of neptunium and plutonium. The results of the calculations have been compared with the available experimental data.

Residual electrical resistivity of dilute nickel alloys

A quantitative calculation of the residual electrical resistivity of dilute ferromagnetic nickel-based alloys has been performed in the framework of the four-current conduction model using the kinetic equation and ab initio approaches for and ab initio approaches for the determination of the scattering potential. The contributions to the residual electrical resistivity from scattering by inhomogeneities of the impurity Coulomb potential and the exchange interaction have been separated by comparing the calculated and experimental data.