Thermoelectric properties of Bi2Se3/Bi2Te3/Bi2Se3 and Sb2Te3/Bi2Te3/Sb2Te3 quantum well systems

In this work, we develop a theory of thermoelectric transport properties in two-dimensional semiconducting quantum well structures. Calculations are performed for n-type 0.1 wt.% CuBr-doped Bi₂Se₃/Bi₂Te₃/Bi₂Se₃ and p-type 3 wt.% Te-doped Sb₂Te₃/Bi₂Te₃/Sb₂Te₃ quantum well systems in the temperature range 50–600 K. It is found that reducing the well thickness has a pronounced effect on enhancing the thermoelectric figure of merit (ZT). For the n-type Bi₂Se₃/Bi₂Te₃/Bi₂Se₃ with 7 nm well width, the maximum value of ZT is estimated to be 0.97 at 350 K and for the p-type Sb₂Te₃/Bi₂Te₃/Sb₂Te₃ with well width 10 nm the highest value of the ZT is found to be 1.945 at 440 K. An explanation is provided for the resulting higher ZT value of the p-type system compared to the n-type system.     

Topological Dirac surface states in ternary compounds GeBi2Te4, SnBi2Te4 and Sn0.571Bi2.286Se4

Using high-resolution angle-resolved and time-resolved photoemission spectroscopy, we have studied the low-energy band structures in occupied and unoccupied states of three ternary compounds GeBi₂Te₄, SnBi₂Te₄ and Sn_0.571Bi_2.286Se₄ near the Fermi level. In previously confirmed topological insulator GeBi₂Te₄ compounds, we confirmed the existence of the Dirac surface state and found that the bulk energy gap is much larger than that in the first-principles calculations. In SnBi₂Te₄ compounds, the Dirac surface state was observed, consistent with the first-principles calculations, indicating that it is a topological insulator. The experimental detected bulk gap is a little bit larger than that in calculations. In Sn_0.571Bi_2.286Se₄ compounds, our measurements suggest that this nonstoichiometric compound is a topological insulator although the stoichiometric SnBi₂Se₄ compound was proposed to be topological trivial.     

Electric quadrupole interaction of111Cd in the system Sb1−xMx (M=Ag,Cd,In,Sn), Sb2Te3, Bi2Te3 and In2Te3

We have performed TDPAC-measurements to investigate the static quadrupole interaction of₁₁₁Cd in the classic semimetal Sb. The coupling constant depends on the concentration of small amounts of metal admixtures. The only exception is the system Sb_1–xAg_x. The temperature dependence of the efg in the narrow gap semiconductors Sb₂Te₃ and Bi₂Te₃ is similar to that one in Te. In contrast to these results the efg in the III–VI-semiconductor In₂Te₃ is temperature independent.     

Bi,Sn and Sb valence states in highT c (Bi,Pb/Sn,Sb)2Sr2Ca2Cu3Oy

The valence of Bi and its substituents Sn and Sb are investigated in the high temperature superconductor (Bi_0.8X_0.15Sb_0.05)₂Sr₂Ca₂Cu₃O_y (often denoted 2223) where X=Pb or Sn. Pb and Sn are isoelectronic with the valence states 2+ and 4+; Bi and Sb are as well with valence states 3+ and 5+. The valence state of Sn and Sb has been obtained from Mössbauer spectroscopy: they exist in the high charge states 4+ and 5+ respectively. Sn, Sb, and presumably Pb, take on the high valence state, and so furnish electrons to the conduction band. This is probably the reason why, although the (Pb, Sb)-doping aids in stabilizing the 2223 crystal structure, it is detremental to the electronic properties which lead to the superconducting phase. The valence state of Bi has been studied using X-ray photoelectron spectroscopy (XPS). These results show clearly that the Bi-based superconductor has a metal-like density of states at the Fermi level, and that the valence in the (Pb, Sb)-doped compounds is less than 3. This very surprising change in valence will have a profound effect on the superconducting properties, and is probably associated with the high valent states of Pb, Sn and Sb.     

Photoconductivity in amorphous chalcogenide thin films: Effect of incorporation of Bi,Sb and Te IN Ge22Se78 binary alloy

Temperature and intensity dependence of steady state photoconductivity is studied in amorphous thin films of various chalcogenide glasses with a view to see the effect of incorporation of Bi, Sb and Te in Ge-Se system. Our results show that the photosensitivity decreases as 10 at % of Bi, Sb and Te are incorporated in Ge₂₂Se₇₈.Transient photoconductivity measurements have also been made on the same samples. These results show that the decay of photoconductivity becomes slower when Bi, Sb and Te are incorporated. The results have been explained in terms of the defect states which are introduced after incorporation of these elements in the binary system.     

用DV－4光谱仪分析航空结构钢中Pb、Sn、As、Sb、Bi

本文介绍了分析航空结构钢中Ｐｂ、Ｓｎ、Ａｓ、Ｓｂ、Ｂｉ残余元素的一种新的快速方法──发射光谱分析法，找出了最佳分析参数，建立了校准曲线，经精密度和准确度试验后，相对标准偏差为１．２５％－９．１０％，结果令人满意。     

纯硒中杂质元素的ICP-AES测定

电感耦合等离子体-原子发射光谱同时测定纯硒中的碲、铅、铋、锑、铜、铁、镍、铝、锡、砷和硼12种元素的含量,优化出各元素的分析波长和分析条件;用基体匹配补偿基体效应,方法简单,快速可靠,样品回收率为94%-107%.     

Superconductivity of A1-type SnSb,SbTe and TeI alloys

Superconducting A1-type Sn, SnSb, Sb, SbTe, Te, Te I and I films were vapour-quenched on glass substrates quench-coated with CaO. The highest transition temperature is exhibited by 100 Å thick 20Sn–80Sb films, which become superconducting at 21.6 K.     

Switching phenomena in amorphous thin films of Ge,Cd x Te y and Sb x Se y

The threshold and memory switching effects in amorphous thin films of Ge, Cd _x Te _y and Sb _x Se _y , prepared by cathodic sputtering and vacuum evaporation are investigated. The switching is dependent on the polarity and the material of the contacts. The memory effect is typical for Ge and Cd _x Te _y films whilst the threshold effect sustaining a repeating frequency of about 0·1 Hz was found with Sb _x Se _y , films. The proper switching time was 0·2–0·4 s for the samples under consideration. A considerable variance of the critical intensity of the electric field when the switching set in was observed, as well as a variance of its dependence on the temperature and the surface properties of the substrate. With Ge samples the switching depended on the total amount of energy accumulated in them. A simple model is proposed on the ground of the achieved results assuming electronic processes in the first phase of the duration of the switching (i.e. injection from electrodes into the amorphous film) and bulk thermal processes leading to the creatin of a conduction channel in the second phase.     

Calculated cross sections for the single ionization of atoms (N, Cu, As, Se, Sn, Sb, Te, I, Pb) by electron impact

By correcting some primary parameters in the semi-classical Deutsch--M?rk (DM) formula, this paper calculates the absolute single electron-impact ionization cross sections of atoms N, Cu, As, Se, Sn, Sb, Te, I and Pb from threshold to 10000eV. The calculated cross sections are compared with available experimental data and other theoretical results. An excellent agreement was achieved between the calculated and measured cross sections for these atoms over a wide range of impact energies.     

Thermal characterization of Se78Ge22 and Se68Ge22M10 (M=Cd,In, Pb) chalcogenide glasses

The paper reports studies on the glass transition kinetics of Se₇₈Ge₂₂ and Se₆₈Ge₂₂M₁₀ (M?=?Cd, In, Pb) chalcogenide glasses. Differential scanning calorimetry (DSC) was performed at different heating rates under non-isothermal conditions. Different kinetic parameters, such as glass transition temperature (T _g) and the activation energy of the glass transition (E _t) have been calculated to investigate the effects of Cd, In and Pb additives on the glass transition kinetics of glassy Se₇₈Ge₂₂ alloy.     

Structure and electrical properties of Sb2Te3 and Bi0.4Sb1.6Te3 metastable phases obtained by HPHT treatment

We have obtained the metastable phase of the thermoelectric alloy Bi_0.4Sb_1.6Te₃ with electron type conductivity for the first time using the method of quenching under pressure after treatment at P=4.0 GPa and T=400–850 °C. We have consequently performed comparative studies with the similar phase of Sb₂Te₃. The polycrystalline X-ray diffraction patterns of these phases are similar to the known monoclinic structure α-As₂Te₃ (C2/m) with less monoclinic distortion, β ≈ 92°. We have measured the electrical resistivity and the Hall coefficient in the temperature range of T=77?450 K and we have evaluated the Hall mobility and density of charge carriers. The negative Hall coefficient indicates the dominant electron type of carriers at temperatures up to 380 K in the metastable phase of Sb₂Te₃ and up to 440 K in the metastable state of Bi_0.4Sb_1.6Te₃. Above these temperatures, the p-type conductivity proper to the initial phases dominates.     

Half-metallicity in Fe-based Heusler alloys Fe2TiZ (Z = Ga,Ge, As,In, Sn and Sb)

The electronic structure and magnetic properties of new Fe-based Heusler alloys Fe₂TiZ (Z = Ga, Ge, As, In, Sn and Sb) have been studied by first-principles calculations. In these alloys, the 24-electron Fe₂TiGe, Fe₂TiSn are nonmagnetic semiconductors and other compounds are all ferrimagnetic metals. Fe₂TiAs and Fe₂TiSb are predicted to be half-metals with 100% spin polarization. The spin polarization ratio in Fe₂TiGa and Fe₂TiIn is also quite high. The calculated total moment for Fe₂TiAs and Fe₂TiSb is 1 μ_B, which is mainly determined by the Fe partial moment. The half-metallicity of Fe₂TiSb is stable under lattice distortion. The spin polarization of Fe₂TiSb is found to be 100% for the lattice variation in a range of 5.6–6.1 Å, which is attractive in practical applications.     

Spin polarization and transport of surface states in the topological insulators Bi2Se3 and Bi2Te3 from first principles

We investigate the band dispersion and the spin texture of topologically protected surface states in the bulk topological insulators Bi2Se3 and Bi2Te3 by first-principles methods. Strong spin-orbit entanglement in these materials reduces the spin polarization of the surface states to ～50% in both cases; this reduction is absent in simple models but of important implications to essentially any spintronic application. We propose a way of controlling the magnitude of spin polarization associated with a charge current in thin films of topological insulators by means of an external electric field. The proposed dual-gate device configuration provides new possibilities for electrical control of spin.     

High pressure transport characteristics of Bi2Te3, Sb2Te3, and BiSbTe3

This paper presents ambient and high pressure measurements of transport properties of the Bi₂Te₃–Sb₂Te₃ series of materials. The electrical resistivity, thermal conductivity, and Seebeck coefficient have been measured on both end compounds and the direct solid solution of the two at pressure up to 10 GPa. An additional discussion involving the high pressure structure will be presented. From this, it was determined that these materials undergo at least two structural phase transitions between 0 and 20 GPa and a discussion is presented regarding this and the changes in the transport properties.     

Mössbauer spectroscopic studies of MIIMIVS3 (MII=Sn,Pb; MIV=Sn,Ge, Hf) and PbSnS2Se

Temperature-dependent Mössbauer experiments have been carried out to examine the lattice dynamical properties of tin sites in Sn₂S₃ and its related compounds. The differences in the lattice parameters, estimated from the temperature dependence of the area intensities for the compounds, are attributed to the characteristics of their crystal structures.     

ICP-AES测定铜-锌合金中锌及杂质元素砷、铅、锑和铋

采用ICP-AES同时测定铜-锌合金中锌、砷、铅、锑和铋含量,优化了样品溶样条件.方法检出限为0.0003%-0.0012%,回收率为86%-112%,RSD为0.30%-5.17%,测试结果表明,该方法是测定铜锌合金的简单准确快速的方法.