Electrical conductivity,thermoelectric power and dielectric constant of NiWO4

The a.c. electrical conductivity ( _ac), thermoelectric power () and dielectric constant () of antiferromagnetic NiWO₄ are presented. _ac and have been measured in the temperature range 300 to 1000 K and in the temperature range 600 to 1000 K. Conductivity data are interpreted in the light of band theory of solids. The compound obeys the exponential law of conductivity = ₀ exp (–W/kT). Activation energy has been estimated as 0.75eV. The conductivity result is summarized in the following equation =2.86 exp (–0.75 eV/kT)^–1 cm^–1 in the intrinsic region. The material is p-type below 660 K and above 950 K, and is n-type between 660 and 950 K.     

Electrical conductivity,thermoelectric power and optical absorption studies of amorphous and crystalline gallium antimonide thin films

Amorphous films (240–1740 Å thick) of gallium antimonide were formed by vacuum evaporation onto goldseal glass slides and onto sodium chloride crystals. They were annealed in successive cycles to obtain the ideal amorphous state. The heat treatment was continued until the crystalline phase was obtained. The electrical conductivity, the thermoelectric power with respect to bulk silver and the optical absorption were measured in all these films before and after crystallization. The electron diffraction patterns of the as-deposited, the annealed and the crystalline films were obtained using a transmission electron microscope. The activation energy for conduction ΔE, the amorphous-to-crystalline transition temperature, the density of states at the Fermi level N(_EF) and the optical energy gap E_o were evaluated.     

The thermoelectric power of someThCe alloys

Measurements of thermoelectric power have been made on someThCe alloys in the temperature range 2–300 K. A modified version of the Nordheim-Gorter rule has been used to obtain the contribution from scattering by the Ce atoms. The results up to 70 K can be understood in terms of the model of nonmagnetic 4f states in agreement with other recent work on this alloy system.     

Electrical conductivity,thermoelectric power and dielectric constant of a Gd2Ti2O7 single crystal

Electrical conductivity, thermoelectric power and dielectric constant of a Gd₂Ti₂O₇ single crystal have been studied in the temperature range 300–1000 K. Gd₂Ti₂O₇ is found to be an-type semiconductor with energy band gap 1.5 eV. It exhibits an extrinsic nature up to 675 K and an intrinsic nature above 675 K. The thermoelectric power increases with temperature in the region 300–675 K whereas it decreases with temperature in the region 675–1000 K. The dielectric constant increases slowly in the temperature range 300–675 K but this increase becomes fast in the temperature range 675–1000 K.     

Electrical conductivity and thermoelectric power of amorphous Sb2Te3 thin films and amorphous-crystalline transition

The results of electrical conductivity and thermoelectric studies on antimony telluride, a promising thermoelectric material, in the thin film state are reported. Films were vacuum-deposited on to clean glass substrates with thickness between 50 and 200 nm and studied in the temperature interval 300 to 470 K. On heating the as-grown films, there is a sharp fall both in the Seebeck coefficient and the electrical resistivity at around 340 to 370 K for all the films. This is attributed to an amorphous to crystalline transition, which is confirmed by X-ray diffractogram and electron diffraction patterns.[/p]     

Electrical resistivity and thermoelectric power of copper-germanium films

CuGe films over the whole composition range were prepared by the vapour quenching of the alloys onto glass substrates held at 300 K. The electrical resistivity, thermoelectric power and temperature dependence of the films were studied in the temperature range 100–500 K. The observed behaviour of the electrical resistivity and thermoelectric power is understandable on the basis of transmission electron microscopy and electron diffraction observations which indicate three structural regions. Up to 5 at.% Ge in copper the films are single phase with a structure similar to that of pure copper; in the range 5–80 at.% Ge in copper the films consist of a mixture of Cu₃Ge, copper and germanium; beyond 80 at.% the CuGe films are single-phase amorphous.     

The kinematic viscosity of liquid copper-aluminum alloys

The method of damped torsional vibrations of crucible with liquid under investigation is used for measuring the temperature dependences of kinematic viscosity ν of Cu_{100 ? x} Al _x melts (x = 0–100 at.%) in the range of temperatures t between the liquidus and 1100–1450°C. Unlike the majority of such experiments, the measurements are performed both in the process of heating the sample after its melting and in the course of subsequent cooling. The branching of ν(t) curves corresponding to the foregoing modes is revealed below certain temperatures dependent on the composition of sample (viscosity hysteresis). The curves obtained under cooling have a simple exponential shape predicted by activation theories of viscous flow. The obtained temperature dependences are used for constructing isotherms of kinematic viscosity, on which maxima are observed in the vicinity of stoichiometric concentration of CuAl₃ and composition of Cu-30 at.% Al. For the same compositions, extrema are observed on the concentration dependence of activation energy of viscous flow.     

Thermal properties of Sn-based solder alloys

During last few decades, emerging environmental regulations worldwide, more notably in Europe and Japan, have targeted the elimination of Pb usage in electronic assemblies due to the inherent toxicity of this element. This situation drives to the replacement of the Sn–Pb solder alloy of eutectic composition commonly used as joining material to suitable lead-free solders for microelectronic assembly. Sn-based alloys containing Ag, Cu, Bi, and Zn are potential lead-free solders, usually close to the binary or ternary eutectic composition. For this reason a great effort was directed to establish reliable thermophysical data fundamental to interpret the solidification process and fluidity of alloys belonging to these systems. In this work, an analysis of the solidification process of pure Sn, binary Sn–Ag, Sn–Cu, Sn–Bi, Sn–Zn, Sn–Pb and ternary Sn–Ag–Cu eutectic alloys was carried out using computer aided-cooling curve analysis and differential scanning calorimetry.     

Electrical resistivity and thermoelectric power of polycrystalline and amorphous Se-Te-Cu system

The dark electrical resistivity and thermoelectric power have been measured for the bulk ternary alloy Se-Te-Cu. The samples were both polycrystalline and amorphous in structure. The measurements were carried out below room temperature. Depending on Cu addition, crystallographic structure, and amorphous or polycrystalline state, the samples manifested semiconducting or metallic behaviour. The maximum difference in electrical resistivity magnitude was of 14 orders. The activation energy ΔE of charge carriers determined for all semiconducting samples ranged from 0.07 to 0.25 eV. An increase in thermoelectric power resulting from the electron–phonon mass enhancement was estimated.     

Absolute thermoelectric power ofAuFe alloys between 0.01 K and 7 K

We present direct measurements of the absolute thermoelectric power of some diluteAuFe alloys at very low temperature using a high-sensitivity voltmeter. The experimental results are discussed in the light of the spin-glass versus Kondo competition.     

Concentration dependence of the anomalous thermoelectric power of dilute magnetic alloys

It has been pointed out recently by one of us (M.S.R.C.) that the variation of the Kondo slopesd (of the /c vs. lnT curves) of dilute magnetic alloys containing a finite solute concentrationc bears a close resemblance to the variation of the functionf (=cos⁶ cos2) with the phase shift for ordinary spin-independent scattering. Sinced is itself primarily determined byf the inference is that is a function ofc when the criterion of infinite dilution is violated. For infinite dilutions theory expects the anomalous thermoelectric power in such alloys to be independent ofc as well as ofT. Taking the experimentally observed extremum in the TEP (S _m) as an approximation to such a TEP, we report, for finite solute concentrations, the variation ofS _m withc, to correspond with the variation off(=cos ⁶ sin2) with . This substantiates the above inference. In fact, one can predict the sign and the variation (withc) ofd, knowing that ofS _m, and vice versa, for a given dilute magnetic alloy system.     

Electrical and thermal conductivity of A319 and A356 aluminum alloys

A rotational contactless inductive measurement technique has been used to measure the electrical resistivity of A319 and A356 aluminum alloys at both solid and liquid states. The method is based on the phenomena that when a conducting material rotates in a magnetic field, circulating eddy currents are induced and generate an opposing torque, which is proportional to the electrical conductivity of the material. The technique was checked and calibrated with pure aluminum where considerable electrical resistivity data exist in the literature. Wiedemann-Franz-Lorenz law was used to estimate the thermal conductivity of A319 and A356 aluminum alloys in liquid state.     

填料粒子形貌对液态灌封胶粘度与热导率的影响

采用40μm球形与无规则形α-Al2O3粒子填充液体硅橡胶,研究了Al2O3粒子用量、形貌对液态灌封胶的粘度与热导率的影响,并用XRD、SEM分析了两种Al2O3的晶型以及在灌封胶中的分布状态。结果表明,在相同的填充量下无规则形Al2O3粒子填充灌封胶的热导率高,球形Al2O3填充灌封胶的可加工性优异。当球形与无规则形填料混合填充的比例为9∶1时可以获得最高的热导率,比单一使用球形Al2O3提高了17.1%。     

Electrical conductivity measurements in liquid metals by rotational technique

The rotational contactless inductive measurement technique has been developed to measure the electrical conductivity of liquid metals. This method is based on the phenomena when a conductor material rotates in a magnetic field, circulating eddy currents are induced and generate a damping torque proportional to the electrical resistivity of the material. The technique was tested to measure the conductivity of five conductors and one low melting composite (LMA-158).