Electronic structure of the BaA1-xBxO3 (A, B = Pb, Bi, Sn, Sb) alloy systems Implications for superconductivity

Coherent potential approximation studies of the electronic structure of the BaA_1-xB_xO₃ (where A and B are different combinations of the elements Pb, Bi, Sn and Sb) alloy systems have been performed with accurate tight-binding hamiltonians. The calculations show how semiconducting BaSnO₃ evolves into a metal upon alloying with Sb or Bi. Common characteristics of the densities of states are pointed out. Using the rigid muffin-tin approximation an analysis of the superconducting properties is given.     

A survey of surface tension,molar volume and density for Sn–Ag–Cu–Bi–Sb quinary alloys as lead-free solders

ABSTRACT

By applying the geometric models and the theoretical equation, the surface tension, the molar volume and the density were studied. The empirical calculations were carried out in temperature range 623?K?≤?T?≤?1123?K. Only few thermophysical properties were estimated for eight quinary alloys: Sn3.55Ag0.5Cu3Bi3Sb, Sn3.48Ag0.5Cu3Bi5Sb, Sn3.48 Ag0.5Cu5Bi3Sb, Sn3.40 Ag0.5Cu5Bi5Sb, Sn3.53Ag1Cu3Bi3Sb, Sn3.46Ag1Cu3Bi5Sb, Sn3.46Ag1Cu5Bi3Sb, Sn3.38Ag1Cu5Bi5Sb. The results show that surface tension and density have a linear appearance for all temperatures. We have also studied the influence of the composition and temperature in the studied alloys. The obtained theoretical results are compared with the experimental ones and with the conventional Pb–Sn welds.     

The effect of sintering temperature on the intergranular properties of Bi2223 superconductors

A systematic study of the intergranular properties of (Bi,Pb)₂Sr₂Ca₂Cu₃O_y (Bi2223) polycrystalline samples has been done using the electrical resistivity and Ac susceptibility techniques. In this project, we have prepared a series of Bi2223 samples with different sintering temperature. The XRD results show that by increasing sintering temperature up to 865 °C the Bi2212 phase fraction decrease. It was found that the Bi2212 phase on the grain boundaries is likely to play the role of weak links and consequently reduces the intergranular critical current densities. Analysis of the temperature dependence of the Ac susceptibility near the transition temperature (T_c) has been done employing Bean's Critical State Model. The observed variation of intergranular critical current densities (J_c) with temperature indicates that the weak links are changed from superconductor–normal metal–superconductor (SNS) for well-coupled sample to superconductor–insulator–superconductor (SIS) type of junctions for the sample with high Bi2212 phase fraction.     

Addition of nanometer SiC in the silver-sheathed Bi2223 superconducting tapes

Nanometer SiC particles were added to (Bi,Pb)₂Sr₂Ca₂Cu₃O_x (Bi2223) precursor powders and the powders were transformed into silver-sheathed superconducting tapes by the standard powder-in-tube (PIT) technique. The influence of SiC on the melting temperature, high-T_c (Bi2223) phase formation, microstructure and transport property of the tapes was studied by means of DTA, XRD, SEM/EDX, electrical and magnetic measurements. The results showed that SiC addition lowered the melting temperature of the superconductor powders and consequently, decreased the optimum sintering temperature of the tapes. However, the addition did not affect the Bi2223 phase formation and critical temperature (T_c) of the tapes up to 1.00 wt.% of SiC. Most importantly, the addition of a small amount of SiC (0.15 wt.%) improved the critical current (I_c) and I_c behavior in magnetic field as a result of the enhancement in density, grain alignment, grain connectivity and flux pinning of the tapes.     

Comparative photoemission study of Bi2(Sr,Ca)3Cu2O8+y and Bi1.7Pb0.3Sr2Ca2Cu3O10+y

The electronic structure of Bi-based 2223 single phase superconductor has been studied by ultraviolet and X-ray photoemission. By comparison with that of 2212 phase superconductor, we find a higher density of states nearE _F for 2223 phase. From analysis of the Cu 2p core-level spectroscopy, we obtain a relatively smaller charge transfer energy between copper and oxygen as well as the Coulomb repulsion energy on Cu site for 2223 phase. We relate these changes to the increase of hole concentration from 2212 to 2223 phase. The experimental results support the viewpoint that the transition temperature should be correlated with the density of states atE _F .     

Specific features of Bi2Te3 doping with Sn

The effect of doping bismuth telluride with tin, on its electrophysical properties, has been studied. It is shown that the main features in the transport coefficients of Bi₂Te₃:Sn can be explained by the existence of resonant Sn states within the valence band. The existence of resonant Sn states was confirmed by codoping Bi₂Te₃:Sn with the electroactive impurity I. Fiz. Tverd. Tela (St. Petersburg) 40, 1428–1432 (August 1998)     

The impact of Y substitution on the 110 K high Tc phase in a Bi (Pb):2223 superconductor

The structural and superconducting properties of Bi_1.7Pb_0.3Sr₂Ca_2−xY_xCu₃O_y superconducting samples are investigated by X-ray diffraction (XRD), resistivity and thermoelectric power (TEP) measurements. XRD results reveal that the volume percentage of the 2223 high T_c phase decreases with an increase in Y content. The replacement of the Ca²⁺ ion by the Y³⁺ ion does not influence the tetragonal structure of the pure Bi (Pb): 2223 system and the lattice parameters vary with Y content. The results of resistivity indicate that the critical temperatures T_c of the samples decrease monotonically with an increase in Y content. Further, the critical concentration of Y to completely suppress superconductivity in the Y-doped Bi (Pb):2223 system is higher (0.60) than that reported (0.20) for the other rare-earth elements. On the other hand, the values of TEP at room temperature are found to be negative for Y=0.00 and 0.10 samples, and it changed to positive with further increase in Y content. The hole-carrier concentration per Cu ion (P) is deduced by using two different ways: the first in terms of T_c values in the superconducting state and the other in terms of TEP values in the normal state. Interestingly, it is found that the values of P deduced from the formal way are not consistent with the reported parabolic behavior for superconducting systems in the under-doped region, and consequently disagree with the general roles of substitution. However, the vice versa is recorded for the values of P deduced from the latter way. The results are discussed in terms of the possible reasons for the suppression of superconductivity in the considered system.     

Study of the occupied and unoccupied electronic states of the Y-substituted (Bi,Pb)-2223 high temperature superconductor

Spectra for the filled and unfilled electronic states of the (Bi,Pb)-2223 high temperature superconductor were recorded by photoemission and fluorescence X-ray absorption in the entire doping range achieved by substitution of bivalent Ca ions with trivalent Y. In photoemission these samples show diminishing spectral intensity near E _F and at 1.5 eV binding energy with increasing Y content. Parallel to the observations for the filled states the O1s X-ray absorption spectra show a decrease and a shift to higher energies of the empty states just above E_F The spectral structures are identified in the framework of the Hubbard model.     

Influence of Sb doping on crystal structure and electrical property of SnO2 nanoparticles prepared by chemical coprecipitation

Sb doped SnO₂ (ATO) nanoparticles with Sb doping concentrations ranging from 0% to 20% (Sb/Sb+Sn) have been prepared by chemical coprecipitation using metallic Sn and SbCl₃ as raw materials. The influence of Sb doping concentration on crystal structure and electrical property was studied in detail. Results indicated that all ATO nanoparticles possessed the same tetragonal rutile structure as that of bulk SnO₂. The average crystal size of the ATO nanoparticles decreased from 16 to 7 nm by increasing the Sb doping concentration. The unit-cell volume of ATO nanoparticles was either expanded or contracted, strongly depending on the Sb doping concentration. The electrical resistivity decreased sharply from 111 to minimum of 1.05 Ω cm when the Sb doping concentration was increased from 0% to 15% and then increased slightly to 1.42 Ω cm when the Sb doping concentration was increased from 15% to 20%. Finally, high resolution X-ray photoelectron spectroscopy (XPS) measurement was employed to investigate the valence state of Sb in samples with various Sb doping levels.     

Raman scattering features of lead pyroantimonate compounds. Part I: XRD and Raman characterization of Pb2Sb2O7 doped with tin and zinc

Yellow pyroantimonates Pb Sb, Pb Sb Sn and Pb Sb Zn were synthesized by solid‐state reactions at high temperature and characterized by X‐ray diffraction and Raman spectroscopy. The lattice size of cubic pyrochlores increases with Sn and Zn doping and with Pb overstoichiometry, indicating the replacement of Sb⁵⁺ by the larger cations. This fact permits the understanding of the corresponding Raman spectral modifications as a consequence of the changes in the local symmetry of the Sb O polyhedra, justifying the exploitation of Raman spectroscopy to noninvasively identify structural modifications of pyroantimonate pigments in artworks. Copyright © 2008 John Wiley & Sons, Ltd.     

萃取分离-石墨炉原子吸收光谱法测定铁镍基高温合金中砷、铅、锡、锑、铋

基于砷、铅、锡、锑、铋与碘离子形成络合物,用MIBK萃取使其与基体分离, 用石墨炉原子吸收光谱法测定了铁镍基高温合金中这五种元素。文章主要对萃取条件及萃取后剩余基体对待测元素的影响进行了研究, 同时采用掩蔽的方法消除了合金中钨、铌、钽的干扰。在所选定的实验条件下,测得砷、铅、锡、锑、铋的回收率范围为93％～99％;相对标准偏差范围为8.8％～12％。     

57Fe,119Sn掺杂Bi2Sr2Can-1CunO2n+4的化学键性质和Missbauer谱位移研究

利用电介质的平均能带模型计算了Bi2Sr2Can-1CuO2n 4(n=1,2,3)的化学化学键参数,应用由共价性和极化率定义的化学环境因子计算^57Fe和^19Sn在Bi2Sr2Can-1CuO2n 4中的Moessbauer同质异能位移,确定了^57Fe和^119Sn在Bi2Sr2Can-1CunO2n 4中的价态和占位情况。     

研磨对Y-123和Bi(Pb)-2223超导相的影响

通过X射线衍射、差热分析、电子显微镜、超导电性测量等手段研究了研磨对Y-123和Bi(Ph)-2223超导相和成相过程的影响。结果表明:研磨对Y-123和Bi(Ph)-2223超导相的影响显著不同,研磨导制了Bi(Ph)-2223超导相的破坏。同时指出Bi(Ph)-2223超导相同一结构特征的两种属性:好的可塑性和结构易破坏性。前者是优点,后者是缺点。在加工、测量、使用过程中,要尽力避免后一缺点带来的超导电性的破坏或由于局部结构破坏而导致的整体性能的降低。     

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。     

Ultrasonic studies of aluminium-substituted Bi(Pb)-2223 superconductors

The compositional dependence of elastic properties of Al³⁺-substituted Bi(Pb)-2223 superconducting system with the general formula Bi_1.7−x Al_xPb_0.3Sr₂Ca₂Cu₃ O_y (x = 0.0, 0.1, 0.2 and 0.3) have been studied by means of ultrasonic pulse transmission (UPT) technique at 1 MHz (300 K). The elastic moduli of the specimens are computed and corrected to zero porosity. The observed variation of elastic constants with aluminium substitution has been explained on the basis of the strength of interatomic bonding. The applicability of heterogeneous metal mixture rule for estimating elastic constants and transition temperature has been tested.     

Interaction of laser light waves by dynamic stark splitting

The internal stresses of condensed films are measured during both, condensation and annealing. Especially, materials are studied which can be stabilized in amorphous phases by quenching condensation technique. All amorphous films of Bi, Bi + Pb, Bi+Sb, Pb+Bi and Sn+Cu grow without any noticeable stress. In contrary, amorphous Sb-films arise with remarkable tensil stresses. The probably important difference between Sb and the other materials consists in the composition of the vapor. At normal evaporation conditions Sb-vapor contains almost only Sb₄-molecules, whereas the other materials evaporate monoatomically. The results are discussed with regard to a modell for the origin of the stresses based on the socalled Ostwald's rule for crystal growth.     

High-spin structures of 51 121, 123, 125, 127Sb nuclei: Single proton and core-coupled states

The ^{121,123,125,127}Sb nuclei have been produced as fission fragments in three reactions induced by heavy ions: ¹²C + ²³⁸U at 90 MeV bombarding energy, ¹⁸O + ²⁰⁸Pb at 85 MeV, and ³¹P + ¹⁷⁶Yb at 152 MeV. Their level schemes have been built from gamma rays detected using the EUROBALL III and IV arrays. High-spin states of ^123,125,127Sb nuclei have been identified for the first time. Moreover isomeric states lying around 2.3 MeV have been established in ^123,125,127Sb from the delayed coincidences between the fission fragment detector SAPhIR and the gamma array. All the observed states can be described by coupling a d_5/2 or g_7/2 proton to an excited Sn core involving either vibrational states or broken neutron pairs.     

Topological surface states in lead-based ternary telluride Pb(Bi(1-x)Sb(x))2Te4

We have performed angle-resolved photoemission spectroscopy on Pb(Bi(1-x)Sb(x))2Te4, which is a member of lead-based ternary tellurides and has been theoretically proposed as a candidate for a new class of three-dimensional topological insulators. In PbBi2Te4, we found a topological surface state with a hexagonally deformed Dirac-cone band dispersion, indicating that this material is a strong topological insulator with a single topological surface state at the Brillouin-zone center. Partial replacement of Bi with Sb causes a marked change in the Dirac carrier concentration, leading to the sign change of Dirac carriers from n type to p type. The Pb(Bi(1-x)Sb(x))2Te4 system with tunable Dirac carriers thus provides a new platform for investigating exotic topological phenomena.     

Doping dependence of the mass enhancement in (Pb,Bi)2Sr2CaCu2O8 at the antinodal point in the superconducting and normal states

Angle-resolved photoemission spectroscopy is used to study the mass renormalization of the charge carriers in the high-T(c) superconductor (Pb,Bi)2Sr2CaCu2O8 in the vicinity of the (pi,0) point in the superconducting and the normal states. Using matrix element effects at different photon energies and due to a high momentum and energy resolution the bonding and the antibonding bands could be separated in the whole dopant range. A huge coupling to a bosonic collective mode is observed below T(c) for both bands, in particular, for the underdoped case. Above T(c), a weaker coupling to a continuous spectrum of modes is detected.     

Laser based angle-resolved photoemission, the sudden approximation, and quasiparticle-like spectral peaks in Bi2Sr2CaCu2O(8+delta)

A new low photon energy regime of angle-resolved photoemission spectroscopy is accessed with lasers and used to study the high T(C) superconductor Bi2Sr2CaCu2O(8+delta). The low energy increases bulk sensitivity, reduces background, and improves resolution. With this we observe spectral peaks which are sharp on the scale of their binding energy--the clearest evidence yet for quasiparticles in the normal state. Crucial aspects of the data such as the dispersion, superconducting gaps, and the bosonic coupling kink are found to be robust to a possible breakdown of the sudden approximation.