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.     

非晶态(Fe1-xCrx)84B16合金的低温热电势

在80—380K之间对(Fe_1-xCr_x)₈₄B₁₆(x=0.01—0.46)非晶态合金的绝对热电势S进行了测量,结果表明,磁性非晶合金的S(T)行为并不都是非线性并有一个浅的极小。少量Cr(x≤0.05)的加入使S的绝对值减小,并使S(T)的极小消失;当Cr含量较多时,样品磁性变弱,S(T)从典型的磁性非晶合金的非线性行为过渡到接近于非磁性非晶合金的线性行为。对x=0.15,0.25的样品,其居里点正落在我们测量的温 关键词：     

Thermoelectric powers of liquid cadmium zinc alloys

The results of new measurements of the absolute thermoelectric power S of liquid cadmium zinc alloys are reported. These measurements extend up to about 730°C for most compositions. A linear dependence of S vs temperature is found. The dependence of S vs concentration, at 450°C, is discussed in the framework of Faber and Ziman's model.     

Spin-glass behaviour of [La,Gd]B6 and [La,Dy]B6 alloys

Electrical resistance and absolute thermoelectric power measurements have been made in the temperature range between 2 and 30 K on a few polycrystalline specimens of [L$\text{a}$,Gd]B₆ and [L$\text{a}$,Dy]B₆ with different concentrations of rare earth ions. The resistance of these alloys varies as $\text{～ T}{}^{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ which is characteristic of spin glasses at low temperature. The thermoelectric power of all specimens but one, shows a broad positive peak in the lower part of the temperature range and becomes negative at higher temperatures, a feature that is typical of a spin glass to paramagnetic phase transition. The exceptional specimen has a large Gd concentration and its thermoelectric power remains positive to higher temperatures than would be expected for a spin glass.     

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.     

The optical properties of liquid metals

Measurements of the dielectric constant, ε₁ + iε₂, have been made on liquid mercury, cadmium, lead and bismuth by a polarimetric method for a range of wavelengths in the visible region. Special attention has been paid to the problem of surface conditions and the final results are believed to be truly representative of the bulk properties of the liquids. The values for the absorption, ωε₂, are found to be consistently higher than those calculated from the free electron Drude theory. This is equivalent to the results of previous workers that a best fit to the Drude equations requires an effective number of electrons slightly greater than the number of valence electrons. Sum rule arguments show that this is to be expected when coupling with the core states is properly taken into account.

Measurements on mercury-bismuth alloys are also reported.     

Peculiarities of the electronic transport in Co2CrAl and Co2CrGa half-metallic ferromagnets

We present results on the transport properties of the half-metallic ferromagnetic Heusler alloys Co₂CrAl and Co₂CrGa in the temperature range from 4 to 900 K. The peculiarities of the resistivity and the absolute differential thermoelectric power are considered within a two-current model of conductivity, taking into account the energy gap at the Fermi level in the electronic spectrum of alloys for electrons with spin opposite to the direction of the magnetization vector.     

Phase equilibria in Hg-He mixtures near the critical point of almost pure Hg

Abstract

The paper presents new high pressure - high temperature experiments on the phase behavior of mercury-helium mixtures. Two distinct fluid phases are shown to exist in Hg-He-mixtures at temperatures and pressures higher than the critical temperature and pressure of pure mercury. Very accurate thermoelectric properties in the immediate vicinity of the critical point of pure fluid mercury show that profound chnages in the electronic structure in that region are manifest in a correspondingly strong thermodynamic state-dependence of the effective interparticle interaction. The latter noticeably influences the features of the phase behavior of pure fluid Hg and the Hg-He-mixtures.     

The reassessment of the structural transition regions along the liquidus of Fe–Si alloys and a possible liquid–liquid structural transition in FeSi2 alloy

We reassessed the structural transition regions along the liquidus of Fe–Si alloys by using ab initio molecular dynamics simulation. Except for 50 at.% Si, structural transition compositions are found at both 30 at.% Si and 67 at.% Si (FeSi₂) which are eutectic alloys. We demonstrated that the liquid structure in the sub-region of 0～30 at.% Si is close-packed, and in the sub-region of 67～100 at.% Si liquid alloys have very open structure. From 30 at.% Si to 67 at.% Si, the close-packed structure gradually change into open one. These structure transition sub-regions are also supported by the formation enthalpy of liquid alloys. Furthermore, the predicted enthalpy change between 1585 K and 1873 K is so large that there is probably liquid–liquid transition with temperature at FeSi₂ alloy which is an important thermoelectric material. Discussions have been made on the materials phenomenon of several Fe–Si alloys based on the structural information.     

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.     

Bi2Te3 合金低温热电性能及冷能发电研究

利用机械合金化和冷压烧结法制备得到n型和p型Bi₂Te₃基热电材料,在80—300 K温度范围测量了电导率、Seebeck系数,结果表明其具有良好的低温热电性能.采用Bi₂Te₃基热电材料制备出半导体热电器件,并配合附属设备搭建出一套半导体温差发电装置.利用液氮汽化时释放的冷能,对半导体热电器件的发电性能进行实验研究,得出这种半导体热电器件输出电压、输出功率与电流关系式,测得最大的输出功率达到1.33 W,从而证明了冷     

The thermoelectric power of type I superconductors in the intermediate state

Measurements of the thermoelectric power of superconducting indium in the intermediate state are reported. A large maximum in the thermoelectric power of crystalline indium is observed with the intermediate state value exceeding the normal state value in the temperature range 0.3 < T/T_c < 1. No maximum is observed in polycrystalline indium.     

Die Änderung der Thermospannung im Magnetfeld (2. Ettingshausen-Nernst-Effekt) bei Kupfer,Silber und Palladium

An experimental device is described for measuring the change in thermoelectric power in magnetic fields (2nd Ettingshausen-Nernst-effect). The change in thermoelectric power was determined for the metals Cu, Ag, Pd at magnetic fields up to 20 kOe at liquid nitrogen temperature. At low magnetic fields there is a proportionality toB ². The temperature dependence of the 2nd Ettingshausen-Nernst-effect is reported for Cu.     

23Na Knight shift of liquid Na-Sn alloys

Measurements of the ²³Na Knight shift in liquid Na-Sn alloys provide strong indications for the formation of compounds about the two distinct compositions Na₄Sn and Na₄Sn₃.     

Electrical and magnetic properties of semimetallic and semiconducting alloys of BiSb

Studies on electrical conductivity, thermoelectric power (t.e.p), Hall effect and diamagnetic susceptibility have been carried out on two inhomogeneous Bi-Sb alloys in the temperature range 100–300 K. Measurements have been confined to the plane perpendicular to the three-fold axis. Antimony impurity levels have been postulated to exist between the bands L_v and L_c. These levels together with the existing band structure of Bi-Sb alloys can explain the observed behaviour of both the alloys of which one is a semimetal and the other a semiconductor. The semiconductor-metal transitions induced by magnetic fields as observed earlier, could also be explained with the help of these antimony levels. The majority of the carriers in both the cases are holes. The different electronic parameters including density of carriers, mobility, nature of the charge carriers and effective masses for all the three bands have been calculated.     

Thermoelectric power and phase transition of polycrystalline As2Te3 under pressure

The pressure dependence of the thermoelectric power of monoclinic As₂Te₃ is measured up to 10 GPa using a Mao-Bell diamond anvil cell. The thermoelectric power never reaches an absolute value greater than the ambient pressure value of 242 μV/K. Evidence of a phase transition is present between 6 and 8 GPa where the thermoelectric power reaches an absolute value of 225 μV/K after passing through a minimum of S≈75 μV/K. X-ray diffraction experiments confirm that the resulting structure is β-As₂Te₃, which is isostructural with Bi₂Te₃ and Sb₂Te₃.     

The thermoelectric properties of quaternary chalcogenides

Abstract

Single phase compounds of the form 1–2₂-3–6, were fabricated using powder metallurgical techniques. Measurements were made of the thermoelectric power, Hall coefficient, electrical conductivity, microhardness and optical reflectance. The electronic properties are discussed in terms of alloy and ionized impurity scattering.     

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 power of cerium at high pressures

The electronic phase transition in cerium occurring near 7 kbar pressure at room temperature which is attributed to the 4f–5d electron promotion has been studied using thermoelectric power as a tool. The important results that have emerged out of this work are: (a) the relatively large variation in the absolute thermoelectric power ofγ-cerium (normal fcc phase) with pressure prior to the phase transition (in contrast to the rather small resistivity change with pressure in this region); (b) a sharp decrease in the thermoelectric power accompanying the iso-structuralγ-α phase transition; and (c) the continuous decrease in the thermoelectric power ofα-cerium (collapsed fcc phase) with pressure, ultimately changing sign at higher pressures. An explanation based on the “virtual bound state” model is proposed to account for these results.     

Electron transport properties of amorphous Mg80.4Cu19.6 alloy

The Hall coefficient, thermoelectric power and electrical resistivity of the liquid quenched amorphous Mg_80.4Cu_19.6 alloy have been measured over a wide temperature range below room temperature. The 2k_F value deduced from the observed Hall coefficient agrees well with the free electron value. The thermoelectric power is positive and increases linearly with increasing temperature above approximately 180 K. The downward deviation is evident in the lower temperature range. This behaviour is in sharp contrast with the negative thermoelectric power observed in the amorphous Mg-Zn alloy. Nevertheless, the overall temperature variation of the electrical resistivity resembles the previously reported data of the amorphous Mg_72.5Zn_27.5 alloy in various aspects; (1) the room temperature resistivity value, (2) the negative TCR and its magnitude, (3) the appearance of a broad maximum at about 50 K and a minimum at about 10 K and (4) T²-dependence in the range of 10～30 K and $\text{-(T-T}{}_{\max }\text{)}{}^{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$-dependence in the range of 50～220 K. The results are discussed in connection with $\text{2k}{}_{\mathrm{F}}\text{K}{}_{\mathrm{P}}$ criterion and Mooij correlation.