Electrical resistivity of liquid Bi–Sb alloys

The electrical resistivities of liquid Bi–Sb alloys have been measured by DC four-probe method within Bi-rich composition through a wide temperature range. The distinct anomaly of a hump shape was observed on resistivity–temperature (ρndash;T) curves for liquid Bi–Sb alloys on heating at the relatively high temperatures. These anomalies have revealed the temperature-induced liquid–liquid phase transition in Bi–Sb melts. The DSC results for BiSb20wt% alloy further prove the existence of liquid–liquid transition. Measuring the ρ–T curves first on heating and then on cooling we have found that on cooling the ρ–T curve remained linear. It means that the postulated liquid–liquid transition may be irreversible.     

Electrical resistivity of microinhomogeneous PdMnxFe1−x alloys

The electronic band-structure calculations of the PdFe ferromagnet and the PdMn antiferromagnet performed in this work permit one to conclude that the specific features of the electrical resistivity observed in the ternary PdMn_xFe_1−x alloy system [the deviation from the Nordheim-Kurnakov rule ρ₀(x)∼x(1−x), which is accompanied by a high maximum of residual resistivity (not typical of metals) ρ ₀ ^m ∼220 μΩ cm at x _C∼0.8 and a negative temperature resistivity coefficient in the interval 0.5≤x≤1] are due to the microinhomogeneous (multiphase) state of the alloys and a variation in the band-gap parameter d spectrum caused by antiferromagnetic ordering of a PdMn-type phase. __________ Translated from Fizika Tverdogo Tela, Vol. 44, No. 2, 2002, pp. 193–197. Original Russian Text Copyright ? 2002 by Kourov, Korotin, Volkova.     

Bulk and surface properties of liquid Sb–Sn alloys

The mixing behaviour of liquid Sb–Sn alloys has been described in terms of energetics and structure through the study of their thermodynamic, surface, transport and structural properties by using the Complex Formation Model (CFM) in the weak interaction approximation and by postulating SbSn chemical complexes as energetically favoured. The new Sb–Sn surface tension experimental data, obtained by the pinned drop method at temperatures ranging from 513 to 1023 K, have been analysed in the framework of the CFM and compared with the calculated values as well as with the corresponding literature data. The structural characteristics of Sb–Sn melts are described by the two microscopic functions, i.e. the concentration fluctuations in the long-wavelength limit and the Warren–Cowley short-range order parameter.     

Surface tension modelling of liquid Cd–Sn–Zn alloys

The thermodynamic model in conjunction with Butler equation and the geometric models were used for the surface tension calculation of Cd–Sn–Zn liquid alloys. Good agreement was found between the experimental data for limiting binaries and model calculations performed with Butler model. In the case of ternary alloys, the surface tension variation with Cd content is better reproduced in the case of alloys lying on vertical sections defined by high Sn to Zn molar fraction ratio. The calculated surface tension is in relatively good agreement with the available experimental data. In addition, the surface segregation of liquid ternary Cd–Sn–Zn and constituent binaries has also been calculated.     

Electrical resistivity and superconductivity of amorphous La−Ag alloys

We report on measurements of the electrical resistivity and the superconducting transition temperature of amorphous La–Ag alloys (60–74 at % La) obtained by liquid quenching. The temperature coefficient of the resistivity is always slightly negativ, its value cannot be described well by existing theories.T _c depends linearly on the La content and seems to be not very sensitive to the second alloy constituent.Dedicated to Prof. Dr. W. Buckel on the occasion of his 60th birthday     

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.     

Abnormal resistivity behavior of Cu–Ni and Cu–Co alloys in undercooled liquid state

The resistivity behavior of undercooled liquid Cu–Ni and Cu–Co alloys had been studied in the contactless method, to probe the structure transition in undercooled melts during the cooling process. Over the entire concentration range, linear behavior of resistivity with temperature was obtained in liquid and undercooled liquid Cu–Ni system. It implied that the formation of icosahedral order might not influence the electron scattering in undercooled liquid Cu–Ni alloys. Similar results were obtained in Cu–Co system in the vicinity of liquidus temperature. A turning point was obvious in temperature coefficient of resistivity for undercooled liquid Cu–Co alloys around the bimodal line, which was interpreted to be responsible for metastable liquid–liquid phase separation. During liquid phase separation process, resistivity decreased and the temperature coefficient of resistivity was larger than that of homogeneous melts. In combination with transmission electron microscopy and scanning electron microscope studies on the as-solidified microstructure, this was interpreted as the formation of egg-type structure and concentration change in Cu-rich and Co-rich phases. The mechanism controlling the separation and droplets motion was also discussed in undercooled liquid Cu–Co system.     

Electrical resistivity of Sn–3.5Ag–xBi solder melts

This article reported the temperature dependence of the electrical resistivity (ρ) of liquid Sn–3.5Ag lead-free solder alloy in continuous heating and cooling processes with varying Bi content in the range of 0, 2, 3.5, 5, and 7?wt.% Abnormal transitions can be observed on ρ–T curves, which indicate liquid–liquid structure transition (LLST) occurs in Sn–3.5Ag–xBi melts. Interestingly, unlike the pattern at first heating cycle, the LLST is reversible during subsequent cooling and heating cycles. Sn may play an important role on the reversibility, and Bi has a noticeable influence on the turning temperatures and characteristics during first heating cycle. The transition mechanism is analyzed from the viewpoint of short-range orders.     

Electrical resistivity of dilute (Cr1−xAlx)95Mo5 alloys

The temperature dependence of the electrical resistivity of (Cr_1−xAl_x)₉₅Mo₅ alloys with x = 0.11, 0.44, 0.77, 1.49, 2.07, 3.11, 4.84, 7.31 and 10.63%, was measured. The non-magnetic behaviour of the antiferromagnetic alloys (x = 0.11, 0.44, 0.77, 1.49, 7.31 and 10.63%) was determined by using the temperature dependence of the alloys with x = 2.07, 3.11 and 4.84% that remain paramagnetic at all temperatures, as a model. This allowed an analysis of the data in terms of existing theories.     

Thermoelectric properties of mechanically alloyed Bi–Sb alloys

Homogeneous polycrystalline Bi_100-xSb_x (x=12, 15, 22) alloys were synthesized by mechanical alloying. The transport coefficients (electrical resistivity, thermal conductivity, and thermopower) were measured, in the 77–300 K temperature range, on samples consolidated either by sintering or extrusion. The thermoelectric figure of merit was deduced from the three coefficients. The temperature dependences are discussed as a function of the alloys’ microstructures taking into account the qualitative effect of potential barriers. Extrusion leads to better performing thermoelectric materials than does sintering. The highest figure of merit is reached for temperatures around 150 K, a temperature at which no reliable thermoelectric material of long service life is available until now. Received: 11 November 1998 / Accepted: 5 January 1999 / Published online: 24 March 1999     

Electrical resistivity of alkali metals: Inflation–deflation effect of Fermi surface

The electrical resistivity of liquid alkali metals was calculated using the extended Ziman formula. The possible role of Fermi surface (FS) inflation–deflation (ID) was examined. The calculations reveal that replacing the sharp free electron FS by the expanded (respectively, contracted) one substantially improves the results. This was achieved directly by considering a FS correction factor of the Fermi radius and indirectly by a shift in the muffin-tin zero (MTZ) of the potential from its initial values. Consequently, a correlation between the shift of the MTZ of the potential and the FS factor parameter is revealed. The role of this correlation might contribute to a better understanding of the electron transport properties of other liquid metals and their alloys.     

Effects of a Cu-contained compound on the microstructures and thermoelectric properties of Zn–Sb based alloys

Zn–Sb based alloys with Cu₂Sb addition were prepared using spark plasma sintering technique and the effects of a Cu-contained intermetallic phase on the microstructures and thermoelectric properties were examined. Rietveld refinement reveals that there are many phases in the alloys, which involve β-Zn₄Sb₃, a major phase ZnSb, a small amount of an intermetallic compound Cu₅Zn₈ and unidentified impurity phases, the quantities of ZnSb and Cu₅Zn₈ increase from 67.3 wt.% to 91.8 wt.% and 0–4.3 wt.% with Cu₂Sb additive increasing, respectively. The ZnSb plays a fundamental role in controlling the thermoelectric properties, and Cu₅Zn₈ is of great significance to optimize the transport properties. The maximum thermoelectric figure of merit ZT of 0.72 is obtained for the alloy (Cu₂Sb)_0.05–(Zn₄Sb₃)_0.95 at 654 K, which is 0.25 higher than that of undoped β-Zn₄Sb₃ at the same conditions. Therefore, we conclude that a proper addition of Cu₂Sb can contribute to the improvement of thermoelectric properties of Zn–Sb based alloys.     

A comparison of genetic programming and neural networks; new formulations for electrical resistivity of Zn–Fe alloys

It is difficult to automatically solve a problem in a systematic method without using computers. In this study, a comparison between Neural Network (NN) and genetic programming (GEP) soft computing techniques as alternative tools for the formulation of electrical resistivity of zinc–iron (Zn–Fe) alloys for various compositions is proposed. Different formulations are supplied to control the verity and robustness of NN and GEP for the formulation to design composition and electrolyte conditions in certain ranges. The input parameters of the NN and GEP models are weight percentages of zinc and iron in the film and in the electrolyte, measurement temperature, and corrosion voltage of the films. The NN- and GEP-based formulation results are compared with experimental results and found to be quite reliable with a very high correlation (R ²=0.998 for GEP and 0.999 for NN).     

Solidification microstructure of as-cast Mg–Zn–Y alloys

Composites consisting of icosahedral (i) phase and ductile α-Mg can be fabricated by controlling the alloy composition. With increasing Mg content, the primary solidification phase changed from the i phase to the α-Mg phase and single eutectic structure can be obtained at a composition of Mg₇₂Zn_23.5Y_3.5. The i phase showed a variation in structural order from the well-ordered icosahedral phase to the 1/1 rhombohedra1 approximant with lattice constants a=27.2 Å and α = 63.43°. The structural change in the i phase can be explained by microdomain formation due to compositional change during solidification. Annealing treatment improves the structural order of the i phase by homogenization. By controlling the alloy composition, a single eutectic structure consisting of a hard i phase and a ductile α-Mg phase could be obtained.     

Volumetric properties of near-eutectic liquid Li–Pb alloys

The density and the thermal expansion of liquid lithium–lead alloys with Pb content of 83.0 and 84.3 at. % was measured using gamma-ray attenuation technique over the temperature range from liquidus to 1000 K. The density change during solid–liquid phase transition was directly measured for the first time for Li15.7Pb84.3 alloy. A comparison of the obtained results with literature data has been carried out.     

Surface tension measurement of metastable liquid Ti–Al–Nb alloys

Thermophysical properties of liquid alloys are usually difficult to measure, especially for high melting point and reactive alloys. In this work, the surface tensions of superheated and undercooled liquid Ti₅₅Al₄₅, Ti₅₀Al₄₅Nb₅ and Ti₄₅Al₄₅Nb₁₀ alloys are determined by using oscillating drop method under electromagnetic levitation state. The experimental results of Ti–Al and Ti–Al–Nb alloys display linear temperature dependence. The maximum undercoolings of 259 (0.143T _L), 268 (0.146T _L) and 275 K (0.147T _L) are respectively achieved for these three alloys. Furthermore, the viscosities of liquid Ti_55−x Al₄₅Nb _x alloys are also derived from the experimental results.     

The evolution of covalent bonding structures of liquid In–Sn alloys

The short-range orders of liquid In_xSn_100−x binary alloys have been investigated along the liquidus based on the experimental results obtained using X-ray diffraction. The covalent bonding structures characterized by the shoulder on the high-Q side of the first peak of S(Q) for all the In_xSn_100−x melts are detected. With increasing Sn content, there is a rather continuous change of the local structure possibly related to the presence of nearly covalent bonds in the liquid alloy. The peculiar temperature dependence of the viscosity is assigned to the evolution of tetrahedral units. The observed correlation between liquid structures and peculiar viscosity behaviors provides new insight into nucleation phenomena from microscopic viewpoint.     

Disorder in liquid Cu–Pd alloys

The disorder in thermodynamic and microscopic structure of liquid Cu–Pd alloy at 1350?K has been studied using regular associated solution model. For this, we have calculated free energy of mixing (G_M ), activity (a), concentration fluctuation in long wavelength limit [S_CC (0)] and chemical short-range order parameter (α ₁) of liquid Cu–Pd alloy at 1350?K. The energetic and structural asymmetry of liquid Cu–Pd alloys has been successfully explained on the basis of regular associated solution model.