Statistical-mechanical perturbation theory for liquid metals

The techniques of statistical mechanical perturbation theory are applied to liquid metals. An ion-ion repulsive pair potential is determined from an experimental structure factor curve at a temperature β₀=1/kT₀. The theory then permits the prediction of radial distribution functions, structure factors, compressibilities, and other properties at all liquid temperatures. As a preliminary test of the theory, it has been used to calculate the isothermal compressibilities of Na, Hg and Ga. The results are in very good agreement with the experimental values, which for the last metals differ from earlier theoretical predictions by almost a factor of five.     

Role of hydrogen in the absorption of ionizing radiation energy by a metal-hydrogen system

Ab initio calculations of the electronic structure of pure Pd, pure Ti, and PdH_x and TiH_x (x = 1, 2, 3) systems are performed within the local density approximation. It is found that the electronic subsystem of metals containing dissolved hydrogen increases their capacity to absorb the energy of electromagnetic radiation and accumulate it for a longer time than pure metals. These two factors promote the nonequilibrium migration of hydrogen atoms and their release from metals upon exposure to ionizing radiation.     

Molecular dynamics simulations on local structure and diffusion in liquid TixAl1−x alloys

The microscopic structure and dynamics of liquid Ti_xAl_1-x alloys together with pure liquid Ti and Al metals were investigated by means of molecular dynamics simulations. This work gives the structural properties, including pair-correlation function, bond-angle distribution function, HA and Voronoi indices, and their composition dependence. The dynamical properties have also been studied. The calculated pair-correlation function, bond-angle distribution function, and HA and Voronoi indices suggest that the stoichiometric composition Ti_0.75Al_0.25 exhibits a different local structure order compared with other concentrations, which help us understand the appearance of the minimum diffusion coefficient at this composition. These results indicate that the mobility of atoms strongly depends on their atomic local structure.     

Surface energies of metals in both liquid and solid states

Although during the last years one has seen a number of systematic studies of the surface energies of metals, the aim and the scientific meaning of this research is to establish a simple and a straightforward theoretical model to calculate accurately the mechanical and the thermodynamic properties of metal surfaces due to their important application in materials processes and in the understanding of a wide range of surface phenomena. Through extensive theoretical calculations of the surface tension of most of the liquid metals, we found that the fraction of broken bonds in liquid metals (f) is constant which is equal to 0.287. Using our estimated f value, the surface tension (γ_m), surface energy (γ_SV), surface excess entropy (−dγ/dT), surface excess enthalpy (H_s), coefficient of thermal expansion (α_m and α_b), sound velocity (c_m) and its temperature coefficient (−dc/dT) have been calculated for more than sixty metals. The results of the calculated quantities agree well with available experimental data.     

Model pseudopotentials and electronic properties of non-transition metals

Two new model pseudopotentials for electron-ion interaction in metals are proposed which contain a single adjustable parameter r_c, the radius of the ion core. The models are used in the evaluation of several properties like electrical resistivity (liquid and solid metals), thermoelectric power, electron dispersion, Fermienergy, density of states and electronic susceptibilities of certain non-transition liquid metals. The obtained results are largely satisfactory with available theoretical and experimental values. The study reveals that the present model pseudopotentials have improved in most of the cases the previous results of other one parameter models.     

A possible role of the surface free enthalpy excess of solid chemical elements in their melting and critical temperature

A 5–20% increase in the average number of neighbors of an atom (n_avrg) in the surface phase between 0 K and melting temperature T_m makes the solid surface “geometrically impossible” to exist at some temperature called the melting temperature. The latter results in the collapse of crystal structure, beginning with the formation of surface layers of liquid a few atoms thick, in agreement with recently published studies. The critical temperature of solid chemical elements is also discussed. The derivation yields expressions for the heat of melting (ΔH_m), entropy of melting (ΔS_m), melting temperature (T_m) and critical temperature (T_c) in case of pure metals.     

The absolute thermoelectric power of polyvalent liquid metals

Results on the measurement of the absolute thermoelectric power of ten polyvalent liquid metals (Al, Bi, Cd, Ga, Hg, In, Pb, Sn, Tl, Zn) from their melting points to about 750°C are reported. The electrical resistivities and the absolute thermoelectric powers of these metals have been calculated using the latest available data on structure factor and Harrison and Animalu form factors. These are compared with the experimental values. It is seen that whereas the predicted and experimental values of the electrical resistivities are in reasonable agreement, those for the absolute thermoelectric power are not. It is suggested that the experimental data on the absolute thermoelectric powers and the resistivities of liquid metals may be used to find the magnitude of the form factor at K = 2k _F.     

General properties of a magnetic-field-induced landau Fermi liquid in high-temperature superconductors and heavy fermion metals

It has been shown that the magnetic-field-induced transition from a non-Fermi-liquid state to a Fermi liquid state in the Tl₂Ba₂CuO_{6 + x} high-temperature superconductor is similar to a transition observed in heavy fermion metals. This behavior is explained in the theory of the Fermi condensate quantum-phase transition implying the existence of Landau quasiparticles. The Fermi condensate quantum-phase transition can be considered as a universal cause of the strongly correlated behavior observed in various metals and liquids such as high-temperature superconductors, heavy fermion metals, and two-dimensional Fermi systems.     

Surface energy of liquid metals at the melting temperature related to bulk liquid structure

The product σχ_Tm of surface energy σ and isothermal compressibility σχ_Tm for liquid metals at the melting temperature T_m yields a length l ranging from about 0.2 to 0.5 Å over the entire range of liquid metals. The variation of l, which has been related brfore to the thickness of the liquid-vapour interface, is shown to be accurately represented by , where the constant c is determined empirically, K_B and N being the Boltzmann factor and Avogadro's number respectively, and S_Tm(0) the bulk liquid structure factor in the long wavelength limit at the melting temperature. A microscopic interpretation of l is proposed.     

The influence of pair potentials on the structure of polyvalent liquid metals

The structure factors of some polyvalent liquid metals show a shoulder on their first peak. We explain these shoulders on the basis of ionic pair potentials : a shoulder is expected near the wave vector 2k_F, the wave length of the oscillations in the metallic pair potentials. To show this quantitatively, we used the “optimized random phase approximation” of Andersen et al.     

Electrical resistivity of ternary glassy and liquid Pd-alloys

The electrical resistivity of liquid (Pd₁₀₀Cu_100?x)₈₀Ge₂₀ alloys has been measured as a function of temperature. For Cu-rich negative temperature coefficients and for Pd-rich alloys positive temperature coefficients of the electrical resistivity have been observed. This behavior is very similar to recent observed resistivity temperature curves of glassy (Pd₁₀₀Cu_100?x)₈₀P₂₀ alloys. An explanation of the resistivity behavior in terms of liquid metals theory is suggested.     

Validity of model-potential approach for the expanded liquid alkali metals

The liquid density along the saturation line is calculated for Na, K, Rb and Cs. Good results are obtained in sodium in the whole experimental range T ? 0.85 T_c (T_c is the critical temperature). The observed discrepancy in the heavier alkali metals for T ? 0.75 T_c is tentatively related to recent speculations.     

The origin of an elastic line in the L 3 x-ray emission spectrum of metallic manganese

A strong elastic line has been found in the L ₃ x-ray emission spectrum of metallic Mn. To unravel its physical nature, the ground-state properties of α-Mn were studied in comparison with those of 3d metals (Cr and Fe in bcc structure), as well as the properties of the L ₃ absorption final states of these three transition metals. To model the electronic structure, LSDA band-structure calculations of Cr, Mn, and Fe were carried out, and L ₃ absorption spectra of these metals were computed in the atomic approximation. A joint analysis of the properties of the ground state and of the final absorption state excited by an x-ray-produced core hole suggests that the elastic line in the α-Mn spectra should be assigned to the specific character of the absorption final-state multiplet.     

Theoretical calculation of the temperature coefficient of surface excess entropy of pure liquid metals

The temperature coefficient of surface excess entropy dS_s/dT of pure liquid metals (Al, Ga and Bi) has been calculated in the framework of Skapski's nearest-neighbor interaction-broken-bond model. It is found that this coefficient varies by 47.2%, 69% and 85% for pure liquids Al, Bi and Ga, respectively, in the temperature range between the melting temperature T_m and T_m + 400 K. The value of the coefficient for pure liquid Ga is an order of magnitude larger than that of Al and Bi. The largest increase in dS_S/dT with temperature occurs in the first 100 K away from T_m, being the largest for liquid Ga which is about 43%. This variation is experimentally inaccessible and therefore lacking in the literature and has never been reported.     

Application of a structure factor-potential relationship to the electrical resistivity of the liquid alkali metals

In the Ziman formulation for the electrical properties of liquid metals, the resistivity depends on an average of the product of the structure factor and the pseudopotential. Ascarelli, Harrison and Paskin have derived a relationship for small wave vector between the structure factor and the pseudopotential for liquid metals such as the alkali metals. This formulation has been used over the entire range of wave vector (k = 0 to 2k _F). The resistivities of Na, K, Rb and Cs calculated with no adjustable parameters are within 25% of the observed values, while Li is underestimated by about a factor of five. The temperature dependencies of all but Li (which is anomalously non-linear) are in similar agreement with experiments made at constant volume.     

Resonant photoemission in DyNi2Mn x rare-earth intermetallides

The electronic structure of the DyNi₂Mn _x rare-earth (RE) intermetallides whose cubic structure is similar to the structure of RT₂ compounds is studied. Resonant photoemission and X-ray absorption methods are used in the vicinity of the 2p- and 3p-excitation thresholds of transition elements and the 3p-, 3d-, and 4d-thresholds of RE metals to find the Ni, Mn 3d-, and R 4f-partial densities of the states in the valent band. The use of resonant photoemission allows us to establish features of the interaction between the unfinished 4f-shells of ions of RE metals with ions of the transition 3d-elements in RNi₂Mn _x compounds. The contributions from atoms of various elements to the structure of the valent band are separated, and the basic regularities of band formation during the introduction of manganese atoms are found.     

Magnetic susceptibility of solid and liquid metals

Apparatus for the measurement of the magnetic susceptibilities of solid and liquid metals at temperatures up to 800°C is described. Prior to studying the susceptibilities of various metals through the melting point, the apparatus was tested by measuring the susceptibilities of tin and lead at room temperature, and the temperature dependences of susceptibility of several pure copper specimens enclosed in quartz bulbs. For copper, in the temperature range 20°C to 700°C,? _χ /?T = 1.9₂ × 10^?11 emu/g · deg C. This result is discussed in terms of the change of electronic susceptibility with volume expansion.     

On the mechanical stability of bcc transition elements and alloys

A volume independent and a volume dependent lattice energy function involving short-range interatomic potentials were able to be fitted to the elastic constants, cohesive energy, lattice parameter and for the latter function to the vacancy formation energy and bcc-fcc lattice stability energy, as well, for fcc metals and bcc alkali metals, but not to the cohesive energy and C' elastic constant of bcc transition metals. The assumption that directional, but partial, covalent bonds exist between nearest-neighbors in the bcc transition elements provides an explanation for the latter results and in addition explains the identical dependence of C' and the bcc-fcc lattice stability upon N_d, where N_d is the average number of d electrons, for the bcc transition metals and alloys. Both the mechanical and thermodynamic stability of the bcc structure for transition metals and all transition metal alloys disappears for 5 ? N_d > 2 and <?1.     

Temperature dependence of low angle structure factors of liquid alkali metals using electron-ion plasma model

The analytic solution of EIP model in the MSA via the OCP criterion yields temperature dependent results in RPA quite satisfactorily at high temperatures. The same set of parameters produces low and high angle structural properties. The model can work almost near to the critical point if the ion-core radius is allowed to vary systematically in the regionρ<2ρ _c,ρ _c being the critical density. The model can also accommodate the general scaling behaviour observed for the structure factors of liquid alkali metals.