Bi Sb Research Articles

Effect of multicomponent modifier on microstructure and mechanical properties of high Ni–Cr–Mo cast iron

The microstructure and mechanical properties of high Ni–Cr–Mo indefinite chilled cast iron with the addition of a newly developed multicomponent modifier consisting of mixed rare earths, Si–Ca alloy and Bi–Sb alloy have been investigated through optical microscopy, X-ray diffraction and scanning electron microscopy, along with hardness, impact toughness and wear resistance measurements. After the addition of the modifier, the grain sizes of the primary austenite and eutectic carbides are found to be greatly refined, and the typically highly continuous net-like carbides become less interconnected but rather appear more blocky shaped. Such microstructure changes lead to mechanical property improvement in the cast specimen, with its hardness increased from 43 to 50 HRC, impact toughness from 6·3 to 7·8 J cm−2 and ⩾20% increase in abrasive wear resistance.

Microstructure and thermoelectric properties of p-type Bi–Sb–Te–Se thin films prepared by electrodeposition method

P-type Bi–Sb–Te–Se thermoelectric thin films with thickness of 8μm have been prepared by cathodic electrodeposition technique on Au substrate from nitric acid solution system at room temperature. Cyclic voltammetry was used for determination of the deposition potentials of the thin films. In order to enhance the crystallinity, as well as the thermoelectric properties of the deposited films, they were annealed at 523K for 2h under nitrogen atmospheric pressure condition. X-ray diffraction (XRD), environmental scanning electron microscopy, and energy-dispersive spectroscopy (EDS) were employed to characterize the thin films. Seebeck coefficients and resistivities of the films were also evaluated. The results revealed that Bi, Sb, Te and Se could be co-deposited to form Bi–Sb–Te–Se semiconductor compound in the solution containing BiIII, SbIII, TeIV and SeIV and the compositions of the films were sensitive to the electrodepositing potentials. The XRD results suggested that the crystal structure of the thin films were changed from amorphous state to polycrystalline after annealing. The EDS data indicated that the composition of the films was consistent with XRD results. The annealed Bi–Sb–Te–Se thin films exhibited the Seebeck coefficients of 116–133μV/K and a maximum power factor of 0.62mW·K−2·m−1.

Thermoelectric properties of p-type Pb-doped Bi 85Sb 15− xPb x alloys at cryogenic temperatures

In this study we have investigated the effect of the Pb on the thermoelectric propertied of Bi–Sb alloy with different Pb-content. The Pb-doped Bi 85Sb 15− x Pb x ( x = 0, 0.5, 1, 2, 3) alloys were synthesized by mechanical alloying followed by pressureless sintering. The crystal structure was characterized by X-ray diffraction. The Seebeck coefficients, electrical conductivities, and thermal conductivities were measured in the temperature range of 77–300 K. The results show that all the Pb-doped alloys are p-type thermoelectric materials in the whole measurement temperature range. A minimum thermal conductivity of 1.7 W/mK was obtained for Bi 85Sb 12Pb 3 sample at 150 K. A maximum ZT value of 0.11, which is higher than those previous reported, was obtained for Bi 85Sb 14Pb 1 at 210 K.

Recent Advances in the Growth of Bi–Sb–Te–Se Thin Films

Thin films of Bi₂Te₃, Sb₂Te₃ and Bi₂Se₃ have been intensively studied during the past ten years both as the best thermoelectric materials operating near room temperature and also as an excellent material with which to explore the newly-discovered form of quantum matter called topological insulators (TI). In this review, we first recapitulate the fundamental properties of bulk forms of these materials, then discuss recent progress in fabrication of thin films and superlattices of these narrowgap semiconductors, discuss their transport properties relevant to their effectiveness as thermoelectric materials, and finally give an outlook on this material system for both fundamental study and applications in thermoelectric energy conversion.

Effects of modification on microstructure and properties of ultrahigh carbon (1.9 wt.% C) steel

Abstract The effects of a modifier that contains Rare Earths (RE), low melting point alloy (Al–Bi–Sb) and Ca–Si alloy on an ultrahigh carbon steel containing 1.9 wt.% C were studied. Microstructure characterization was carried out with optical microscopy (OM) and scanning electronic microscopy (SEM) combined with energy-dispersive spectrometry (EDS). Upon modification, the continuous eutectic carbide network structure was broken up and changed to a partly isolated and finer blocky structure in the as-cast alloy. Differential scanning calorimetry (DSC) revealed that the eutectoid temperature increased and the eutectic temperature decreased for the modified alloy. Modification also improved the impact toughness of the tempered steel, with a significant increase from 6.5 to 12.6 J cm −2 , despite the hardness remaining around 66 HRC. Furthermore, in pure sliding under loads of 20, 60 and 100 N for 600 s against a zirconia ball, the modified alloy shows slightly higher friction coefficient at all loads than the non-modified one. In addition, the friction coefficient for the steel specimen decreased with load from 20 N to 100 N attributing to a reduction in metallic wear and the formation of a thicker oxide film on the surfaces.

C60‐doping of nanostructured Bi–Sb–Te thermoelectrics

AbstractNew bulk nanocomposite thermoelectric materials composed from nanocrystallites of Bi–Sb–Te alloys covered by C60 molecules have been synthesized and studied. The fullerene molecules provide thermal phonons blocking and particular charge transfer in the nanocomposite. The molecules act as electron traps, and thus decrease the density of free electrons in n‐type semiconductor and generate holes in p‐type materials. The capture of electrons is not accompanied by shifts of the Raman bands in C60 spectra. The density of free charge carriers and their Hall mobility change nonmonotonically with the increase of fullerene content in Bi–Sb–Te–C60 nanocomposites. The maximum value of thermoelectric figure of merit ZT = 1.15 was obtained in p‐type nanocomposite that is 30% higher than in the undoped starting material. The observed phenomenon provides new ways for transport properties optimization of thermoelectric materials and thermoelectric devices efficiency increase.

Preparation and characterization of Bi-doped antimony selenide thin films by electrodeposition

Bi-doped antimony selenide (Sb 2− x Bi x Se 3) thin films have been prepared by potentiostatical electrodeposition and post annealing treatment. Cyclic voltammetry (CV) was used to investigate the electrochemical behaviors of electrodeposition. The suitable deposition potential for film preparation was determined to be about −0.40 V vs. SCE combining with CV, energy dispersive X-ray spectroscopy (EDS), environmental scanning electron microscope (ESEM) studies. After annealing, film shows improved crystallinity and a basic orthorhombic Sb 2Se 3 structure but having a larger d-spacing due to the substitution of Bi for Sb in Sb 2Se 3 lattice. The annealed film exhibits an absorption coefficient of larger than 10 5 cm −1 in the visible region, an direct optical band gap of 1.12 ± 0.01 eV, the n-type conductivity, an carrier concentration of 1.1 × 10 19 cm −3 and an flat band potential of −0.40 ± 0.03 V vs. SCE.

Observation of Dirac Holes and Electrons in a Topological Insulator

We show that in the new topological-insulator compound Bi(1.5)Sb(0.5)Te(1.7)Se(1.3) one can achieve a surfaced-dominated transport where the surface channel contributes up to 70% of the total conductance. Furthermore, it was found that in this material the transport properties sharply reflect the time dependence of the surface chemical potential, presenting a sign change in the Hall coefficient with time. We demonstrate that such an evolution makes us observe both Dirac holes and electrons on the surface, which allows us to reconstruct the surface band dispersion across the Dirac point.

Comparison of the Valence Band Structure Peculiarities in the Bi0.84–Sb0.16–Sn0.1 and Pure Semiconducting Bi1-xSbx Alloys

On the basis of measured low magnetic field galvanomagnetic coefficients both for Sn-doped Bi0.84–Sb0.16–Sn0.1 and pure semiconducting Bi–Sb alloys, kinetic parameters of the investigated materials have been determined. It is shown that hole ellipsoids corresponding to the obtained results are less anisotropic (ν2/ν1 = 0.05, ν3/ν1 = 0.5) in comparison with L-hole ellipsoids, where ν2/ν1 = 0.009, ν3/ν1 = 0.7 and their slope is significantly larger (φh = 16°) than L-hole (and L-electron) ones. Therefore peculiarities of the valence band for the Bi0.84–Sb0.16 alloy and other semiconducting alloys with high content of antimony can not be adequately described by involving dominant contribution of the hole valleys localized in T, H, and L points of the Brioullin zone.

Comparison of the Valence Band Structure Peculiarities in the Bi0.84–Sb0.16–Sn0.1and Pure Semiconducting Bi1-xSbxAlloys

On the basis of measured low magnetic field galvanomagnetic coefficients both for Sn-doped Bi0.84–Sb0.16–Sn0.1 and pure semiconducting Bi–Sb alloys, kinetic parameters of the investigated materials have been determined. It is shown that hole ellipsoids corresponding to the obtained results are less anisotropic (ν2/ν1 = 0.05, ν3/ν1 = 0.5) in comparison with L-hole ellipsoids, where ν2/ν1 = 0.009, ν3/ν1 = 0.7 and their slope is significantly larger (φh = 16°) than L-hole (and L-electron) ones. Therefore peculiarities of the valence band for the Bi0.84–Sb0.16 alloy and other semiconducting alloys with high content of antimony can not be adequately described by involving dominant contribution of the hole valleys localized in T, H, and L points of the Brioullin zone.

Mineralogical, fluid inclusion and stable isotope characteristics of Birimian orogenic gold mineralization at the Morila Mine, Mali, West Africa

Gold mineralization at Morila is hosted in flat-lying meta-graywacke associated with a Birimian-aged Massigui schist belt in Mali. Three major events of deformation/metamorphism/fluid flow (D 1, D 2 and D 3) are recognized at Morila, with mineralization associated with various increments of deformation and fluid flow during D 2. Three distinct vein sets V 1–V 3, associated with D 1–D 3 respectively, have also been recognized. V 1 vein sets are thin, poorly defined, quartz–feldspar metamorphic segregations broadly parallel to the regional fabric. V 2 veins are generally boudinaged, foliation-parallel quartz–feldspar veins, or occur as felsic melt segregations in the form of quartz–K feldspar–muscovite–biotite blebs located essentially within the ore-zone. V 3 veins occur as sub-parallel to high angle biotite–arsenopyrite–gold veins that appear to be extensional in nature. The ore zone is characterized by compositionally distinct biotite (higher MgO and lower FeO) and more calcic plagioclase than otherwise texturally identical minerals in the footwall and hanging wall of the mineralized zone, suggesting that prograde metamorphic minerals were modified by post-metamorphic Mg- and Ca-rich mineralizing fluids. Gold forms discrete grains in the V 2 veins or in the adjacent host rock, and is closely associated with pyrrhotite and arsenopyrite. Gold also occurs with Sb–Bi ore minerals in rare microfractures. Numerous thin biotite–arsenopyrite–gold veinlets cut D 1 and D 2 fabrics, and often carry significant gold associated with kink bands in the D 2 fabric. Fluid inclusion and oxygen isotope study provide evidence that Morila fluids are intermediate salinity (12–16 wt.% NaCl equivalent), NaCl–CaCl 2–MgCl 2–H 2O–CH 4–N 2 fluids of magmatic origin (δ 18O water = 10.9 ± 0.3‰). The ore-forming fluid subsequently unmixed to form a compositional range of vapor-rich CH 4–N 2, dilute NaCl ± CH 4–N 2 aqueous and liquid-rich brine associated with the opening of a micro-fracture network and vein development. Quartz–biotite isotope geothermometry indicates that mineralization occurred between 350° to 450 °C. Gold mineralization at Morila was an integral part of coeval plutonism, deformation and regional metamorphism, while the modification of the ore fluid by unmixing was the most important factor associated with the concentration of economically viable gold grades at Morila.

Detection of internal cracks and ultrasound characterization of nanostructured Bi 2Te 3-based thermoelectrics via acoustic microscopy

The search for thermoelectric (TE) materials for highly efficient devices aims at improving the TE efficiency and broadening their areas of applications. We created nanostructured thermoelectric Bi–Sb–Te-family materials by high energy (ball milling) pre-treatment of the parent materials followed by high-pressure/high-temperature treatment. Bi 0.5Sb 1.5Te 3 compositions with the superfluous maintenance of tellurium was used for the synthesis of the samples with p-type electrical conductivity. Acoustic microscopy was used to study elastic properties and bulk irregularities and to detection of internal cracks both in the parent materials and in the created nanostructured samples. The data has been used for optimization of parameters of synthesis of nanostructured thermoelectrics.

Electrical and thermal transport properties of electrically stressed Bi–Sb–Te nanocrystalline thin films

Nanoscale size effect is beneficial for enhancing thermoelectric figure-of-merit of Bi–Sb–Te compounds due to the decrease of thermal conductivity. Bi–Sb–Te nanocrystalline thin films prepared by sputtering at room temperature, in general, require a post-deposition treatment to improve their electrical transport properties by eliminating residual crystal defects. In this study we present an electric current stressing treatment to effectively eliminate crystal defects in sputtered Bi–Sb–Te films at low temperature. By maintaining a low thermal conductivity of 0.6–0.7 W/mK, the electrically stressed Bi–Sb–Te nanocrystalline films possess highly enhanced Hall mobility and moderately reduced carrier concentration as compared to the films thermally treated at the same temperature. Carrier concentration, mobility and Seebeck measurement results suggest that the change of electrical transport properties involves the elimination of Sb Te antisite defects as supported by the observation of some Sb-rich precipitates in the thermally/electrically treated Bi–Sb–Te films. Besides, crystal defects are also suggested to be preferentially removed in the (00 l)-oriented grains due to anisotropic diffusion and electrical transport properties in the electrically stressed Bi–Sb–Te films.

A fluid inclusion and isotopic study of an intrusion-related gold deposit (IRGD) setting in the 380 Ma South Mountain Batholith, Nova Scotia, Canada: evidence for multiple fluid reservoirs

A set of sheeted quartz veins cutting 380 Ma monzogranite at Sandwich Point, Nova Scotia, Canada, provide an opportunity to address issues regarding fluid reservoirs and genesis of intrusion-related gold deposits. The quartz veins, locally with arsenopyrite (≤5%) and elevated Au–(Bi–Sb–Cu–Zn), occur within the reduced South Mountain Batholith, which also has other zones of anomalous gold enrichment. The host granite intruded (P = 3.5 kbars) Lower Paleozoic metaturbiditic rocks of the Meguma Supergroup, well known for orogenic vein gold mineralization. Relevant field observations include the following: (1) the granite contains pegmatite segregations and is cut by aplitic dykes and zones (≤1–2 m) of spaced fracture cleavage; (2) sheeted veins containing coarse, comb-textured quartz extend into a pegmatite zone; (3) arsenopyrite-bearing greisens dominated by F-rich muscovite occur adjacent the quartz veins; and (4) vein and greisen formation is consistent with Riedel shear geometry. Although these features suggest a magmatic origin for the vein-forming fluids, geochemical studies indicate a more complex origin. Vein quartz contains two types of aqueous fluid inclusion assemblages (FIA). Type 1 is a low-salinity (≤3 wt.% equivalent NaCl) with minor CO2 (≤2 mol%) and has T h = 280–340°C. In contrast, type 2 is a high-salinity (20–25 wt.% equivalent NaCl), Ca-rich fluid with T h = 160–200°C. Pressure-corrected fluid inclusion data reflect expulsion of a magmatic fluid near the granite solidus (650°C) that cooled and mixed with a lower temperature (400°C), wall rock equilibrated, Ca-rich fluid. Evidence for fluid unmixing, an important process in some intrusion-related gold deposit settings, is lacking. Stable isotopic (O, D, S) analyses for quartz, muscovite and arsenopyrite samples from vein and greisens indicate the following: (1) δ18Oqtz = +11.7‰ to 17.8‰ and δ18Omusc = +10.7‰ to +11.2‰; (2) δDmusc = −44‰ to−54‰; and (3) δ34Saspy = +7.8‰ to +10.3‰. These data are interpreted, in conjunction with fluid inclusion data, to reflect contamination of a magmatic-derived fluid ( $$ {\delta^{{{18}}}}{{\hbox{O}}_{{{{\rm{H}}_{{2}}}{\rm{O}}}}} $$ ≤ +10‰) by an external fluid ( $$ {\delta^{{{18}}}}{{\hbox{O}}_{{{{\rm{H}}_{{2}}}{\rm{O}}}}} $$ ≥ +15‰), the latter having equilibrated with the surrounding metasedimentary rocks. The δ34S data are inconsistent with a direct igneous source based on other studies for the host intrusion ( $$ {\delta^{{{18}}}}{{\hbox{O}}_{{{{\rm{H}}_{{2}}}{\rm{O}}}}} $$ = +5‰) and are, instead, consistent with an external reservoir for sulphur based on δ34SH2S data for the surrounding metasedimentary rocks. Divergent fluid reservoirs are also supported by analyses of Pb isotopes for pegmatitic K-feldspar and vein arsenopyrite. Collectively the data indicate that the vein- and greisen-forming fluids had a complex origin and reflect both magmatic and non-magmatic reservoirs. Thus, although the geological setting suggests a magmatic origin, the geochemical data indicate involvement of multiple reservoirs. These results suggest multiple reservoirs for this intrusion-related gold deposit setting and caution against interpreting the genesis of intrusion-related gold deposit mineralization in somewhat analogous settings based on a limited geochemical data set.

Thermoelectric Properties of P-Type Bismuth Telluride Powders Synthesized by a Mechano-Chemical Process

P-type bismuth telluride thermoelectric (TE) powders were synthesized by a mechano-chemical process (MCP) in which a mixture of Bi sulfate, Sb chlorides, and TeO2 powders was dried, calcinated, and reduced to a powder alloy with ternary composition. The synthesized powders were a few micrometers in size, with a clear Bi0.5Sb1.5Te3 phase. The powders were consolidated into p-type bismuth telluride bulk materials that exhibited an electrical resistivity of 0.6×10−5 Ωm, a Seebeck coefficient of 140 μVK−1, and a thermal conductivity of 1.3 Wm−1K−1 at 298 K. Dimensionless figures-of-merit increased from 0.8 to 1.18 as the temperature increased from 298 K to 450 K. The results show that MCP is a promising process for the production of p-type bismuth telluride powders as raw materials for high-performance TE bulk alloys.

Crystal structure of natural orthorhombic Ag0.71Pb1.52Bi1.32Sb1.45S6, a lillianite homologue with N = 4; comparison with gustavite

The crystal structure of natural orthorhombic Ag0.71Pb1.52Bi1.32Sb1.45S6, a lillianite homologue with N = 4, from hydrothermal veins at Kutna Hora in central Bohemia, Czech Republic, has been refined from single-crystal X-ray data to final R w = 5.08 %. The symmetry is orthorhombic, space group Cmcm , with a = 4.2539(8), b = 13.3094(8), c = 19.625(1) A, V = 1111.1(2) A3, Z = 4. On the basis of electron-microprobe analysis, the formula is Ag0.69Pb1.56(Bi1.32Sb1.37)∑=2.69(S6.04Se0.01)∑6.05 with N chem = 3.94, Bi/(Bi + Sb) = 0.49 and a gustavite substitution percentage L% = 70.5, which characterize the phase as a natural orthorhombic Sb–Bi 4,4L member of the lillianite homologous series. The structure contains seven independent positions: three metal sites M 1, M 2 and M 3 and four sulphur positions. The crystal structure consists of blocks of diagonal chains of four octahedra M 1 (Bi/Ag/Sb) – M 2 (Sb/Pb/Bi) – M 2 – M 1 separated by Pb atoms in bicapped trigonal prismatic coordination of the site M 3. The marginal octahedron of the chain of four octahedra is formed by one mixed site M 1 containing 52 % Bi, 35.6 % Ag and 12.4 % Sb while the central M 2 octahedron is a mixed site containing 60.1 % Sb, 25.9 % Pb and 14 % Bi. The mixed population of the M 1 site results in orthorhombic symmetry, space group Cmcm , with a 4 A a -repeat while in natural gustavite, the alternating occupation of the M 1 site by Ag and Bi atoms (which are thus two sites M 1a and M 1b) reduces the symmetry to monoclinic, space group P 21/ c , with an 8 Arepeat. The structure is similar to that of Ag-free lillianite.

The effect of the precursor nanopowder size on the thermoelectric properties of nanostructured Bi–Sb–Te bulk materials

This paper presents the effect of precursor powder size on the thermoelectric properties of sintered nanostructured bulk materials. The transport properties of the nanostructured bulk show a dramatic size effect. There are a lower thermal and electrical conductivity for the bulk with smaller nanopowders. The dimensionless figure-of merit values ( ZT) of almost all the samples are much lower than those of the list reported data in the paper because the decrease in the thermal conductivity is counteracted by the reduction in the electrical conductivity and the Seebeck coefficient. The combination route of hydro/solvothermal synthesis and spark-plasma-sintering method provide a well controlled way to significantly reduce the thermal conductivity.

Electric current enhanced defect elimination in thermally annealed Bi–Sb–Te and Bi–Se–Te thermoelectric thin films

An electric-current assisted thermal treatment is demonstrated to be an effective process for eliminating crystal lattice defects and improving thermoelectric properties of both Bi–Sb–Te and Bi–Se–Te nanocrystalline thin films. A model based on electromigration-induced preferential Sb and Te diffusion is proposed to explain the observed Sb-rich and Te precipitation as well as the enhancement of Seebeck coefficient and electrical conductivity of the electrically stressed thin films. Owing to anisotropic diffusion and electrical transport properties, charged lattice defects are preferentially eliminated in the direction parallel to the basal plane of bismuth telluride crystal under electric current stressing. The presented current assisted annealing approach can be an efficient postdeposition treatment that prevents from gross grain growth and evaporation of volatile constituents in Bi–Te based nanocrystalline thin films during high-temperature annealing process.

Identifying the Specific Nanostructures Responsible for the High Thermoelectric Performance of (Bi,Sb)2Te3 Nanocomposites

Herein, we report the synthesis of multiscale nanostructured p-type (Bi,Sb)(2)Te(3) bulk materials by melt-spinning single elements of Bi, Sb, and Te followed by a spark plasma sintering process. The samples that were most optimized with the resulting composition (Bi(0.48)Sb(1.52)Te(3)) and specific nanostructures showed an increase of approximately 50% or more in the figure of merit, ZT, over that of the commercial bulk material between 280 and 475 K, making it suitable for commercial applications related to both power generation and refrigeration. The results of high-resolution electron microscopy and small angle and inelastic neutron scattering along with corresponding thermoelectric property measurements corroborate that the 10-20 nm nanocrystalline domains with coherent boundaries are the key constituent that accounts for the resulting exceptionally low lattice thermal conductivity and significant improvement of ZT.

Deformation twinning of Bi–Sb solid alloy formed under a strong gravitational field

We performed an ultracentrifuge experiment on Bi–Sb alloy. Deformation twins with misorientations of about 90° were observed in the low-gravitational region where grain refinement had not occurred. The twins were thicker than the conventional deformation twins and their thickness was proportional to the gravitational field. We found that the minimum gravitational field required for grain refinement was 0.17 × 106 G at 240°C for periods <10 h.