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.     

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.     

Electrical and thermal conductivities and Seebeck coefficient of liquid copper–bismuth alloys

The electrical resistivity and absolute thermoelectric power of the liquid Cu _x –Bi_{(1? x )} system have been measured over the whole composition range from the liquidus to 1100°C. The thermal conductivity is deduced from measurements of these two properties. The experimental results are interpreted and discussed in term of the extended Faber–Ziman formula using the t-matrix formalism with hard-sphere structure factors. The concentration and energy dependence of the phase shifts have been taken into account for a complete conductivity and thermopower calculation.     

Electrical and thermoelectrical properties of selenium-tellurium liquid alloys

A study has been made of the electrical conductivity and thermoelectric power of liquid alloys Te_1-x Se _x with 0≤-x≤-0.5. The temperature range extends from undercooling to about 900°C for electrical conductivity and 750°C for thermoelectric power. A partial conservation after melting of covalent bonds between the atoms of the chains leads to a liquid model in which Gubanov's theory predicts an energy band gap. The experimental results in the intrinsic semiconductor range give the band gap and the mobility ratio values. The thermal gap changes from 1.2 to 3 ev between pure tellurium and the alloy with 70 at. % selenium. There is a large increase in hole mobility with atomic % selenium. For x≥0.2 the low temperature results of the electrical conductivity can be explained by the existence of localized states in the band gap. The high temperature measurements show a trend to the metallic state, but this state cannot be reached at one atmosphere pressure even for tellurium.     

Effect of impurities on thermoelectric power due to phonon drag in metals

The effect of inelastic impurity scattering of electrons on the thermoelectric power due to phonon drag in metals has been studied. It is shown that this is the main cause of the thermoelectric power suppression due to doping at low temperatures. The thermoelectric power in a metal with a quadratic electron spectrum has been calculated as a function of temperature and impurity concentration. In addition to the impurity concentration, the correction to the thermoelectric power due to inelastic scattering contains the large factor Θ_D/T. Zh. éksp. Teor. Fiz. 111, 2237–2242 (June 1997)     

Electrical properties of CuTlSe2 in the liquid state

The electrical conductivity and thermoelectric power of CuTlSe₂ have been investigated as a function of temperature up to 230 °C above its melting point. In the liquid state the experimental data are analyzed in terms of a model developed for the density of states and electrical transport in solid amorphous semiconductors (Mott, 1970). Positive thermoelectric power suggests a large predominance of holes in electrical conduction. It appears that the conduction is due to holes in extended states near the band edge. It is found that the energy gap has a large temperature coefficient =5.5×10^–4eV/K.     

Electrical properties of polycrystalline TiO<Subscript>2·</Subscript> Thermoelectric power

The present work determined thermoelectric power for high-purity polycrystalline TiO₂ at elevated temperatures (1,123–1,323 K) and in the gas phase of controlled oxygen activity, . The slope of the thermoelectric power vs logp(O₂) is 1/10, instead of 1/6 expected by the theory and observed for TiO₂ single crystal. The discrepancy between the two is considered in terms of the effect of the local grain boundary structure on thermoelectric power. A comparison between the electrical conductivity and thermoelectric power data indicates that the oxygen activity values related to the n–p transition point determined by thermoelectric power are lower than those determined by electrical conductivity. This project was performed as part of UNSW R&D program on solar–hydrogen.     

Thermoelektrische Eigenschaften reiner Metalle in der Umgebung der Schmelztemperatur

The thermoelectric power of the face-centered cubic metals copper, silver, gold and aluminium was measured in the vicinity of the melting temperature. For all four metals mentioned a discontinuous change of the absolute Seebeck coefficient towards more positive values was found at the melting point. — Values of the thermoelectric power of liquid metals may be calculated with a model using the correlation function of the ions and their pseudopotentials as proposed byZiman. The results agree, at least qualitatively, with the measured values.     

The absolute thermoelectric powers of some liquid alloys

Measurements of the absolute thermoelectric powers of several liquid alloys as a function of temperature and composition are reported.

The alloys Hg-In and Hg-Tl were studied. In both cases the absolute thermoelectric powers show a minimum when plotted against concentration at low concentrations.

The system Hg-Na was measured over the range 0 at. % to 10 at. % Na. The absolute thermoelectric power shows a very sharp minimum at about 5.0 at. % Na. This minimum becomes sharper with increasing temperature. The effect is more marked in this case than in the previous two cases.

Measurements of absolute thermoelectric power of the alloys of cadmium in mercury and gold in mercury show that it becomes less negative as the metals are added to mercury. This is the opposite effect to that found in the previous two alloys.

Measurements made on the Cd-In system show no minimum. The results on these alloys are discussed with relation to Mott's theory for liquid mercury (Mott 1966).     

Electrical properties of the AgTlSe2 semiconductor in the liquid state

The electrical conductivity and thermoelectric power of AgTlSe₂ have been investigated as a function of temperature from 390° C up to 590° C. The experimental data are analyzed in terms of a model developed for the density of states and electrical transport in solid amorphous semiconductors [12]. Positive thermoelectric power suggests a large predominance of holes in electrical conduction. It appears that the conduction is due to holes in localized states near the band edge.     

Transport properties of liquid iron up to 6 Gpa

Abstract

The electronic thermal conductivity λ_e(T, p) is determined by application of the Wiedemann-Frans relation with the Lorens function L(T) as obtained at 1 atmosphere, to electrical conductivity data obtained from two sets of high p, T measurements through the polymorphic phases into the liquid atate of pure Iron. Values of Δλ_e(T, p)/Δp in the liquid state vary between 42. 6 and 52. 4[mW cm^?1 K^?1 GPa^?1].Contributions to variations of the Lorens number L(T, p) are discussed in terms of the density of levels Nd(C) and the changes of the Fermi energy ? with p, T as obtained from data on the thermoelectric power S(T, p) variations combined with the electrical conductivlty u(T, p) variations, both determined from high presaure experimental values for did and liquid iron.     

Spin treatment-based approach for electronic transport in paramagnetic liquid transition metals

A novel concept is proposed to calculate both the electrical resistivity and thermoelectric power (TEP) of liquid transition metals (Mn, Fe, Co and Ni) characterized by a paramagnetic state in the liquid phase. By contrast to a previous work (PRB64, 094202 (2001)), where the resistivity was calculated by treating separately the interactions between spin up and spin down using the Matthiessen rule, our current approach is based on two types of muffin tin potentials in the t-matrix, namely spin up and spin down. The resistivity is treated as the result of the interference of the two kinds of spin states of electrons including a cross-contribution. The calculated resistivity values agree reasonably well with the available experimental ones for all the metals considered. Moreover, the calculated TEP, as deduced from the slope of resistivity vs. energy, has been found to be positive for Mn and Fe but negative for Co and Ni. Besides that, this formalism for resistivity calculation may be generalized to a system that may exist in different atomic states. It is worth mentioning that this concept is analogous to the one used in the process of neutron scattering on a metal composed of multiple isotopes.     

Electronic transport properties of liquid InSn20 alloy

In this article, temperature dependences of the electrical conductivity σ and the absolute thermoelectric power S of InSn20 wt% melt were investigated. Abnormal phenomena were observed on both σ–T and S–T curves within certain temperature range, suggesting a temperature-induced liquid structural change occurred in the melt. Combined with the data of the mean neighbor distance r ₁ obtained by the prior X-ray diffraction, according to Faber–Ziman theory, the temperature functioning patterns of the density of states N(E_F ) and its gradient value dN(E_F )/dE were deduced. The results reflect that the electronic structure of the melt at Fermi level also changes during the transition.     

Electrical resistivity of noble and transition metals using Animalu's model potential

Calculations of the electrical resistivity of several solid noble and transition metals have been carried out using the transition metal model potential proposed by Animalu. It has been found that, except for Cu, Ag and Au, the calculated resistivities of solid transition metals are considerably below the experimental values indicating that the Animalu's model potential fails to account for the electrical resistivities of transition metals. The failure of the Animalu's model potential has been discussed.     

Theoretical calculations of the temperature dependence of the electrical and thermal conductivities of liquid gallium

The electrical and thermal resistivities of liquid gallium are calculated over a range of temperatures above the melting point using the solutions of the Boltzmann equation. The experimental x-ray structure factor of Waseda and the form factor derived using the Heine-Abarenkov model potential are used in these calculations. The ratio of the electrical and thermal conductivities is calculated and compared to experimental values and to the theoretical Lorenz number.     

Change of absolute thermoelectric power of gold and platinum due to lattice defects

The temperature dependence of the extra-thermoelectric power of gold and platinum after quenching or after plastic deformation was measured in the temperature range from –190°C to 20°C. It was found that dislocations raise the absolute thermoelectric power of gold, whereas vacancies reduce it. In platinum both kinds of defects reduce the absolute value of the thermoelectric power in the whole range of temperatures.Gold was quenched from different temperatures into water and the change of electrical resistivity and of thermoelectric power was simultaneously measured. The extra-thermoelectric powerS varies directly with the concentration of vacancies. Its value is given by the relationS/c=–1·08 V/(grad at. % vac.) The activation energy of the formation of lattice vacancies in gold wasE _F =(0·93±0·14) eV.The analysis of the experimental results was carried out at this institute.     

Electrical properties and thermal conductivity of AgTlTe2 in the solid and liquid phases

Measurements of the electrical conductivity, thermelectric power and thermal conductivity of an AgTlTe₂ semiconductor in the solid and liquid states were carried out in a wide range of temperatures. In the liquid state the data analyzed in terms of a model developed for the density of states and electrical transport in solid amorphous semiconductors. Positive thermoelectric power suggests a large predominance of holes in electrical transport.     

Thermoelectric composite materials based on intermediate-valence cerium and ytterbium intermetallic compounds

An important thermoelectric characteristic-the power factor of composite thermoelectric materials—is calculated on the basis of performed measurements of the thermopower, electric conductivity, thermal conductivity, and reference data. The investigated composites consist of intermediate-valence CeNi and YbAl₃ intermetallic systems and elementary metals, nickel and chromium. On account of the specific transport properties of a heterogeneous medium, it becomes possible to increase the value of the power factor in composites at a sufficiently low concentrations of rare-earth-element-based intermetallic compounds. The dependences of the composite-thermoelectric-material power factor on the temperature and the mass fraction of valence-instable components are obtained.     

A significant enhancement in thermoelectric power factor of In2Te3 thin films by Se doping and Te composition tuning

Thermoelectric power factor of a material significantly relies on its electrical conductivity, thermal conductivity, and Seebeck coefficient. Herein, an attempt has been made to enhance the thermoelectric power factor of In₂Te₃ thin films by tuning their Te composition and via Se doping. The optimum Se-doping concentration and Te composition enhanced the power factor of pristine In₂Te₃ films by 14 and 7.4 times, respectively. The modified chemical composition, structural characteristics, and surface morphological features of In₂Te₃ films are observed to be pivotal in improving their thermoelectric power factor. Overall, this study offers a facile approach to control the thermoelectric power factor of In₂Te₃ thin films which is significant for their futuristic applications.     

Phase transition and high temperature thermoelectric properties of copper selenide Cu2-x Se （0 ≤ x ≤ 0.25）

With good electrical properties and an inherently complex crystal structure, Cu_2-xSe is a potential “phonon glass electron crystal” thermoelectric material that has previously not attracted much interest. In this study, Cu_2-xSe (0 ≤ x ≤ 0.25) compounds were synthesized by a melting-quenching method, and then sintered by spark plasma sintering to obtain bulk material. The effect of Cu content on the phase transition and thermoelectric properties of Cu_2-xSe were investigated in the temperature range of 300 K—750 K. The results of X-ray diffraction at room temperature show that Cu_2-xSe compounds possess a cubic structure with a space group of Fm3m (#225) when 0.15 < x le 0.25, whereas they adopt a composite of monoclinic and cubic phases when 0 ≤ x ≤ 0.15. The thermoelectric property measurements show that with increasing Cu content, the electrical conductivity decreases, the Seebeck coefficient increases and the thermal conductivity decreases. Due to the relatively good power factor and low thermal conductivity, the nearly stoichiometric Cu₂Se compound achieves the highest ZT of 0.38 at 750 K. It is expected that the thermoelectric performance can be further optimized by doping appropriate elements and/or via a nanostructuring approach.