Physicochemical Properties of Sn-Zn and SAC + Bi Alloys

Applying the discharge crucible (DC) method, the viscosity, density, and surface tension were determined for Sn-9Zn and Sn-2.92Ag-0.4Cu-3.07Bi (SAC + Bi) alloys. For comparison, the dilatometric, maximum bubble pressure, and capillary flow methods were used for measurements of these same physicochemical properties for the Sn-2.92Ag-0.4Cu-3.07Bi (SAC + Bi) alloy. The measurements were performed for Sn-9Zn and SAC + Bi alloys in the temperature range from 513 K to 723 K and 530 K to 1180 K, respectively. The experimental data obtained show that addition of Bi to SAC increases the density and decreases the surface tension and viscosity in comparison with SAC solder. Additionally it was found that the properties studied by different methods (maximum bubble pressure, dilatometric, capillary flow, and discharge crucible) were almost identical.     

Surface tension measurements of the Bi-Sn and Sn-Bi-Ag liquid alloys

The maximum bubble pressure method has been used to measure the surface tension of pure Bi, surface tension and density of liquid binary Bi-Sn alloys (X_Bi = 0.2, 0.4, 0.6, and 0.8 molar fractions) at the temperature range from about 500 K to 1150 K. Similarly, there were investigated ternary alloys adding to the eutectic (3.8/at.%Ag-Sn) 0.03, 0.06, 0.09, and 0.12 molar fractions of Bi. The linear dependencies of densities and surface tensions on temperature were observed and they were described by straight-line equation. It has been confirmed that the additions of Bi to liquid Sn and to the eutectic alloy (3.8at.%Ag-Sn) markedly reduce the surface tension. Experimental data of the surface tension of liquid Bi-Sn were compared with modeling based on Butler’s method and a reasonable agreement was observed.     

Evaluation of the Thermoelectric Module Consisting of W-Doped Heusler Fe2VAl Alloy

Power generation performance of a thermoelectric module consisting of the Heusler Fe₂VAl alloy was evaluated. For construction of the module, W-doped Fe₂VAl alloys were prepared using powder metallurgy process. Power generation tests of the module consisting of 18 pairs of p–n junctions were conducted on a heat source of 373–673 K in vacuum. The reduction of thermal conductivity and improvement of thermoelectric figure of merit by W-doping enhanced the conversion efficiency and the output power. High output power density of 0.7 W/cm² was obtained by virtue of the high thermoelectric power factor of the Heusler alloy. The module exhibited good durability, and the relatively high output power was maintained after temperature cycling test in air.     

Surface-tension measurements of the eutectic alloy (Ag-Sn 96.2 at.%) with Cu additions

The maximum bubble-pressure method has been used to measure the surface tension and density of liquid alloys (Ag-Sn)_eut + Cu (X_Cu = 0.005, 0.020, 0.0375, and 0.065 (mole fraction)). The surface tension and density measurements were curried out in the temperature ranges of 262–942°C and 264–937°C, respectively. The linear dependencies of surface tensions and densities on temperature were observed, and they were described by straight-line equations. It has been found that the additions of Cu to the Ag-Sn eutectic alloy increase the surface tension. Experimental data of the surface tension were compared with those from modeling based on Butler’s method, using the optimized-thermodynamic parameters from the literature, and a slight tendency contrary to the experimental results was observed.     

Sn addition on the tensile properties of high temperature Zn–4Al–3Mg solder alloys

The Zn–4Al–3Mg based solder alloy is a promising candidate to replace the conventional Pb–5Sn alloy in high-temperature electronic packaging. In this study, the tensile properties of Zn–4Al–3Mg–xSn alloys (x = 0, 6.8 and 13.2 wt.%) at high temperatures (e.g., 100 °C, and 200 °C) were investigated. It was found that the uniaxial tensile strength (UTS) of Zn–4Al–3Mg–xSn solder alloys all decrease monotonously with the increment of temperature. The elongation ratio at 100 °C is superior to that at room temperature whereas follows a significant drop at 200 °C. The microstructure observations show that a typical brittle fracture of Zn–4Al–3Mg alloy occurs at room temperature and 200 °C under normal tension, whereas a ductile fracture is found at 100 °C. The 6.8 wt.% Sn addition in Zn–4Al–3Mg alloy causes a dramatic decrease of yield strength, and a slight deterioration of the ductility.     

Effect of Alloying Elements on the Electrification–Fusion Phenomenon in Sn-Based Eutectic Alloys

The effect of alloying elements on the electrification–fusion phenomenon in Sn-based eutectic alloys (Sn-9Zn and Sn-37Pb) under alternating current was investigated in this study. Experimental results showed that the critical fusion current densities (CFCD) of Sn-based alloys were closely related to both the conductivity of the individual phase and the eutectic temperature. While the electrical current density value required to trigger microstructural evolution for the Sn-9Zn alloy was larger than the CFCD of pure Sn (1399 A/cm²), that for the Sn-37Pb alloy was not. Through in situ examination of the microstructural evolution during electrification–fusion tests, the initial liquation site emerged from individual Sn-based eutectic phase (i.e., the Sn/Zn eutectic phase or Sn/Pb eutectic phase); The liquation regions in the Sn/Zn eutectic phase and β-Sn phase of the Sn-9Zn alloy were not concentrated over the observation area. The liquation regions in the Sn/Pb eutectic phase and β-Sn phase of the Sn-37Pb alloy were extensively distributed over the observation area. According to the fusion distributed density at the observation area, the Sn-9Zn alloy has great potential to replace the Sn-37Pb alloy in future electrification applications.     

Reducing Lattice Thermal Conductivity of the Thermoelectric Compound AgSbTe2 (P4/mmm) by Lanthanum Substitution: Computational and Experimental Approaches

In this study we performed lattice dynamics first-principles calculations for the promising thermoelectric (TE) compound AgSbTe₂, and estimated the stability of its three polymorphs over a wide temperature range from 0 to 600 K. We calculated the vibrational density of states of the AgSbTe₂ (P4/mmm) phase. The results suggested that formation of substitutional defects at Ag-sublattice sites impedes lattice vibrations, thereby reducing lattice thermal conductivity. We focused on calculations based on the Debye approximation for the compound La_0.125Ag_0.875SbTe₂, and predicted reduction of the average sound velocity from 1684 to 1563 m s^?1 as a result of La doping. This is manifested as a ca. 14% reduction in thermal conductivity. To confirm the results from computation we produced two Ag–Sb–Te-based alloys, a ternary alloy without La addition and a quaternary alloy containing La. We measured the thermal conductivity of both alloys by use of the laser flash analysis method, and, as a result of La alloying, observed a reduction in thermal conductivity from 0.92 to 0.71 W m^?1 K^?1 at 573 K, as calculated from first principles.     

Phase Stability and Thermoelectric Properties of CuFeS2-Based Magnetic Semiconductor

Recently, based on measurement results below 400 K, we suggested that chalcopyrite CuFeS₂-based alloys hold promise as thermoelectric materials. In this study, we have investigated the phase stability of such compounds and measured their thermoelectric properties at temperatures above 400 K. Thermogravimetric data indicate that the samples synthesized by a spark plasma sintering method were stable up to 700 K, above which sulfur deficiency becomes prominent. The electrical resistivity of the electron-doped samples showed metallic behavior up to 700 K. The Seebeck coefficients show large negative values of about ?300 μV/K above 400 K. As a result, the power factor of Cu_0.97Fe_1.03S₂ is ~1 mW/K²m in the temperature range of 400 K to 600 K.     

Electronic and Magneto-Transport Across the Heusler Alloy (Co2FeAl)/p-Si Interfacial Structure

Electronic and magneto-transport across the Heusler alloy Co₂FeAl (CFA)/ p-Si structure have been studied. The morphology of the Heusler alloy film surface has also been characterized by atomic force microscopy and magnetic force microscopy (MFM). X-ray diffraction data revealed formation of the CFA alloy phase with the L2₁ structure. MFM results revealed formation of a fine domain structure of average size ～10 nm and magnetic signal strength 0.23°. The I–V characteristics are strongly temperature-dependent between ～80 K and 300 K for forward bias, compared with weak temperature dependence on reversing the polarity. At low temperature the I–V characteristics have the features of a backward diode. The observed strong temperature dependence is because of thermionic emission of carriers across the interface. The weak temperature dependence is because of dominant field-emission tunnelling of carriers across the interface. Large magnetic field sensitivity of the reverse current has also been observed. The observed magnetic field sensitivity for the reverse current shows the involvement of electronic spin in transport across the interface, from the Heusler alloy to the silicon. An MR of ～35% in the presence of a magnetic field was estimated from the I–V data. The study has shown that spin-dependent tunnel transport from the CFA alloy to silicon across the interface results in the observed value of MR, which seems to be because of spin scattering.     

Thermoelectric Properties of Al-Doped ZnO Thin Films

We have prepared 2 % Al-doped ZnO (AZO) thin films on SrTiO₃ substrates by a pulsed laser deposition technique at various deposition temperatures (T _dep = 300–600 °C). The thermoelectric properties of AZO thin films were studied in a low temperature range (300–600 K). Thin film deposited at 300 °C is fully c-axis-oriented and presents electrical conductivity 310 S/cm with Seebeck coefficient ?65 μV/K and power factor 0.13 × 10^?3 Wm^?1 K^?2 at 300 K. The performance of thin films increases with temperature. For instance, the power factor is enhanced up to 0.55 × 10^?3 Wm^?1 K^?2 at 600 K, surpassing the best AZO film previously reported in the literature.     

The study of structural,electronic, elastic and optical properties in Be1−xZnxTe alloys

Structural, optical and electronic properties, elastic constants of Be_1−xZn_xTe alloys have been studied by employing Castep program based on density functional theory (DFT). The Generalized Gradient Approximation (GGA) and Local Density Approximation (LDA) were utilized as exchange correlation. Using elastic constants for compounds, bulk modulus, forbidden band gap, Fermi energy and Kramers–Kronig relations; dielectric constants, the refractive index, absorption coefficient, energy loss function have been found through calculations. Apart from these results the elastic constants and bulk modulus were obtained experimentally, using X-ray measurement and Vegard׳s law with aim comparison. These properties of ternary alloys were explored using the properties of binary alloys. It is seen that results obtained from both methods are all in agreement. Be_1−xZn_xTe alloy also shows the alloy ionic character for x=0.25. When the Zn is increased, the ionic property of all alloys is increases. Furthermore, as the alloy with x=0.25 shows a flexible characteristic property, other alloys become brittle one.     

Preparation and Thermoelectric Properties of Doped Bi2Te3-Bi2Se3 Solid Solutions

Since Bi₂Te₃ and Bi₂Se₃ have the same crystal structure, they form a homogeneous solid solution. Therefore, the thermal conductivity of the solid solution can be reduced by phonon scattering. The thermoelectric figure of merit can be improved by controlling the carrier concentration through doping. In this study, Bi₂Te_2.85Se_0.15:D _m (D: dopants such as I, Cu, Ag, Ni, Zn) solid solutions were prepared by encapsulated melting and hot pressing. All specimens exhibited n-type conduction in the measured temperature range (323 K to 523 K), and their electrical conductivities decreased slightly with increasing temperature. The undoped solid solution showed a carrier concentration of 7.37 × 10¹⁹ cm^?3, power factor of 2.1 mW m^?1 K^?1, and figure of merit of 0.56 at 323 K. The figure of merit (ZT) was improved due to the increased power factor by I, Cu, and Ag dopings, and maximum ZT values were obtained as 0.76 at 323 K for Bi₂Te_2.85Se_0.15:Cu_0.01 and 0.90 at 423 K for Bi₂Te_2.85Se_0.15:I_0.005. However, the thermoelectric properties of Ni- and Zn-doped solid solutions were not enhanced.     

Effect of Composition on Thermoelectric Properties of Polycrystalline CrSi2

Ingots with compositions CrSi_2?x (with 0 < x < 0.1) were synthesized by vacuum arc melting followed by uniaxial hot pressing for densification. This paper reports the temperature and composition dependence of the electrical resistivity, Seebeck coefficient, and thermal conductivity of CrSi_2?x samples in the temperature range of 300 K to 800 K. The silicon-deficient samples exhibited substantial reductions in resistivity and Seebeck coefficient over the measured temperature range due to the formation of metallic secondary CrSi phase embedded in the CrSi₂ matrix phase. The thermal conductivity was seen to exhibit a U-shaped curve with respect to x, exhibiting a minimum value at the composition of x = 0.04. However, the limit of the homogeneity range of CrSi₂ suppresses any further decrease of the lattice thermal conductivity. As a consequence, the maximum figure of merit of ZT = 0.1 is obtained at 650 K for CrSi_1.98.     

Thermoelectric Properties of Light-Element-Containing Zintl Compounds CaZn2−x Cu x P2 and CaMnZn1−x Cu x P2 (x = 0.0–0.2)

Light-element-containing CaAl₂Si₂-type Zintl phases CaZn_2?x Cu _x P₂ and CaMnZn_1?x Cu _x P₂ (x = 0.0–0.2) have been synthesized by solid-state reaction. Electrical resistivity (ρ), Seebeck coefficient (α), and thermal conductivity (κ) were measured over a wide temperature (T) range (80–1000 K) to evaluate the thermoelectric potential of these materials. Below 300 K, the power factor (PF; α ²/ρ) is very small. Above 600 K, however, PF increases rapidly for all compositions because of a rapid increase of α and a simultaneous decrease of ρ. The measured large α is consistent with the wider band gap expected for these compositions. Compared with the pure compounds, larger PF values are observed for the Cu-substituted compounds; the largest observed PF is ～0.5 mW/m K². The thermal conductivity is found to be rather low, despite the presence of light elements, and is in the range 1.0–1.5 W/m K at 1000 K. Because of the combination of low κ and moderate PF values, the dimensionless figure of merit ZT = α ² T/ρκ reaches a maximum of 0.4 for CaZn_1.9Cu_0.1P₂.     

Magnetic properties of (FeIn2S4)1 − x (In2S3) x alloy single crystals

(FeIn₂S₄)_{1 ? x} (In₂S₃) _x alloy single crystals are grown by oriented crystallization in the entire range of component concentrations. For the single crystals, studies of the magnetic properties are carried out in the temperature range 4–300 K and the magnetic-field range 0–14 T. It is established that almost all of the alloys are paramagnetic materials at temperatures down to the lowest achievable temperatures (～4 K). It is shown that the ground magnetic phase state of the alloys is the spin-glass state with the freezing temperature steadily increasing with increasing Fe²⁺ cation content. The most probable causes and mechanism of formation of the magnetic state of the (FeIn₂S₄)_{1 ? x} (In₂S₃) _x crystals are discussed.     

Microstructural Investigation,Raman and Magnetic Studies on Chemically Synthesized Nanocrystalline Ni-Doped Gadolinium Oxide (Gd<Subscript>1.90</Subscript>Ni<Subscript>0.10</Subscript>O<Subscript>3−<Emphasis Type="Italic">δ</Emphasis></Subscript>)

Nanocrystalline Ni-doped gadolinium oxide (Gd_1.90Ni_0.10O_3?δ, GNO) is synthesized by co-precipitation method. The as-prepared sample is annealed in vacuum at 700°C for 6 h. Analyses of the x-ray diffractogram by Rietveld refinement method, transmission electron microscopy and Raman spectroscopy of GNO recorded at room temperature confirmed the pure crystallographic phase and complete substitution of Ni-ions in Gd₂O₃ lattice. Magnetization (M) as a function of temperature (T) and magnetic field (H) is measured by a superconducting quantum interference device magnetometer, which suggests the presence of ferromagnetic/antiferromagnetic phases together with a paramagnetic phase. From the M–T curve it can be shown that the ferromagnetic phase dominates over para-/antiferromagnetic phases in the temperature range of 300–100 K, but from 100 K to 50 K, the antiferromagnetic phase dominates over ferro-/paramagnetic phases. Hysteresis loops recorded at different temperatures indicate the presence of weak ferro-/antiferromagnetism, which dominates in the low field region (～ 4000 Oe), above which magnetization increases linearly. The sharp increase of magnetization in M–T curve observed in the temperature range of 50–5 K confirms the presence of dominating ferromagnetic plus paramagnetic phase over antiferromagnetic part. For the first time a combined formula generated from three-dimensional (3D) spin wave model and Johnston formula is proposed to analyze the coexistence of different magnetic phases in different temperature ranges. Interestingly, the combined formula successfully explains the co-existence of different magnetic phases along with their contribution at different temperatures. The onset of ferromagnetism in Gd_1.90Ni_0.10O_3?δ is explained by oxygen vacancy mediated F-centre exchange (FCE) coupling mechanism.     

OMVPE growth of the metastable III/V alloy GaAs0.5Sb0.5

The two crystal growth parameters most likely to affect the occurrence of GaAs_0.5Sb_0.5 spinodal decomposition during organometallic vapor phase epitaxial (OMVPE) growth, substrate temperature and substrate orientation, were investigated in detail. The temperature range studied was the widest over which good morphology layers could be grown, from 550 to 680° C. The InP substrate orientations used were (100), (221) and (311). The growth process was found to be diffusion controlled at high temperatures, but to be controlled by surface kinetics at temperatures below approximately 620° C, depending on substrate orientation. Growth of high quality layers was found to be much easier between 570 and 640° C. In addition, the 77 K PL intensity is much stronger for layers grown in this temperature range. The minimum PL halfwidth at 77 K is 20 meV and at 8 K is 16 meV. The typical room temperature hole mobilities are 100 cm²/Vs with hole concentrations of 2 x 10¹⁷ cm^-3 in undoped material. The temperature dependence of mobility is consistent with enhanced alloy scattering. Surprisingly, the growth temperature has no significant effect on either PL halfwidth or hole mobility between 560 and 660° C. The single Raman line observed for the unannealed alloy is split after annealing into two lines corresponding to the GaAs-rich and GaSb-rich alloys on either side of the range of solid immiscibility. The spinodal decomposition apparently starts at the surface where the coherency strain, which stabilizes the single phase alloy, is smallest.     

Corrosion Behavior of Pb-Free Sn-1Ag-0.5Cu-XNi Solder Alloys in 3.5% NaCl Solution

Potentiodynamic polarization techniques were employed in the present study to investigate the corrosion behavior of Pb-free Sn-1Ag-0.5Cu-XNi solder alloys in 3.5% NaCl solution. Polarization studies indicated that an increase in Ni content from 0.05 wt.% to 1 wt.% in the solder alloy shifted the corrosion potential (E _corr) towards more negative values and increased the linear polarization resistance. Increased addition of Ni to 1 wt.% resulted in significant increase in the concentration of both Sn and Ni oxides on the outer surface. Secondary-ion mass spectrometry and Auger depth profile analysis revealed that oxides of tin contributed primarily towards the formation of the passive film on the surface of the solder alloys containing 0.05 wt.% and 1 wt.% Ni. Scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDX) established the formation of a Sn whisker near the passive region of the solder alloy obtained from the polarization curves. The formation of Sn whiskers was due to the buildup of compressive stress generated by the increase in the volume of the oxides of Sn and Ni formed on the outer surface. The presence of Cl^? was responsible for the breakdown of the passive film, and significant pitting corrosion in the form of distinct pits was noticed in Sn-1Ag-0.5Cu-0.5Ni solder alloy after the polarization experiment.     

Density measurement of Sn-40Pb,Sn-57Bi,and Sn-9Zn by indirect Archimedean method

By the indirect Archimedean method, the density and the density-temperature relationship of the Sn-40Pb eutectic alloy and two Pb-free solders, Sn-57Bi and Sn-9Zn eutectic alloys, were measured from room temperature to about 250°C. The results showed that the density-temperature dependence for each alloy in both solid and melting states can be fitted linearly as ρ_S(Sn-40Pb)=8.51−8.94×10⁻⁴(T−25°C), ρ_L(Sn-40Pb)=8.15−13.8×10⁻⁴(T−T_m); ρ_S(Sn-57Bi)=8.54−5.86 × 10⁻⁴(T−25°C), ρ_L(Sn-57Bi)=8.51−10.9×10⁻⁴(T−T_m); and ρ_s(Sn-9Zn)=7.22−7.78×10⁻⁴(T−25°C), ρ_L(Sn-9Zn)=6.89−5.88×10 ⁻⁴(T−T_m), where the density unit was g/cm³. At the melting point, density of the melt of these solders is 8.15 g/cm³, 8.51 g/cm³, and 6.89 g/cm³, respectively. The density decreased 2.6% for Sn-40Pb eutectic alloy during melting, and 2.7% for Sn-9Zn eutectic alloy, but increased 0.5% for Sn-57Bi eutectic alloy. The excess molar volume for these alloys after mixing at their melting point is 0.03 cm³/mol for Sn-40Pb, 0.09 cm³/mol for Sn-57Bi, and 0.21 cm³/mol for Sn-9Zn.     

Influence of cation-vacancy imperfection on the electrical and photoelectric properties of the Cu1 − x Zn x InS2 alloy

The growth technology of single crystals of Cu_{1 ? x} Zn _x InS₂ alloys (x = 0–12) of n-type conductivity is developed. The formation mechanism of the alloy is investigated by X-ray structural analysis. It is shown that the single crystals have chalcopyrite structure, and the unit-cell parameters depend on the alloy composition. The temperature dependence of the electrical conductivity in the temperature range T = 27–300 K and the spectral distribution of the photoconductivity at T ≈ 30 K are investigated. Induced photoconductivity is found for CuInS₂-ZnIn₂S₄ with a content of ～8 and ～12 mol % ZnIn₂S₄ and thermally stimulated currents are investigated.