Search

High-quality Bi1−xSbx (0 ≤ x ≤ 0.2) bicrystals with nanowidth crystallite interfaces (CIs), exhibiting simultaneously superconductivity (Tc ≤ 21 K) and weak ferromagnetism, are studied. A number of unusual features of quantum transport are observed, which are due to topological changes of the Fermi surface of CIs layers, as well as the manifestation of some 3D topological phases of the matter. It is revealed that the flow of Dirac fermions is sensitive to the field orientation, and the localization process occurs only at the B||CIs plane. In doing so, the dependences of the Landau level index n on peak position B n − 1 at inclination interfaces are extrapolated to −0.5 if 1/Bn → 0, as expected for the massless Dirac fermions, while in crystallites and some twisting CIs with an increased degree of imperfection, electronic states are of the Schrodinger type, since n takes integer values. At Sb concentrations of x ∼ 0.04, the high-field thermomagnetic phenomena of CI layers exhibit behavior of the 3D topological semimetals, whereas in bicrystals with 0.07 ≤ x ≤ 0.2 they manifest typical features of the 3D topological insulators. [ABSTRACT FROM AUTHOR]

In this paper, we report a number of atypical features of superconductivity, weak ferromagnetism, and quantum transport observed at low temperatures at bicrystalline interfaces of the first predicted and experimentally realized three-dimensional topological insulator (3D TI) Bi1xSbx (0 ≤ x ≤ 0.2). Pure bicrystals and bicrystals slightly doped (≤0.01 at %) with Te (donor) and Sn (acceptor) impurities are used to fully satisfy the conditions of manifestation of transport quantum oscillations. These 3D TI interfaces exhibit fascinating quantum topological properties, which require extensive basic and applied research.In presentul articol raportăm o serie de caracteristici atipice ale supraconductibilităţii, feromagnetismului slab și transportului cuantic observate la temperature joase la interfețele bicristaline ale primului izolator topologic tridimensional (3D TI), prezis și realizat experimental in aliajele Bi1xSbx (0 ≤ x ≤ 0.2). Bicristale pure și ușor dopate (≤0.01 at. %) cu impurități deTe (donor) și Sn (acceptor) au fost utilizate pentru a satisface pe deplin condițiile de manifestare a oscilațiilor cuantice de transport. Aceste interfețe 3D TI manifestă proprietăți topologice cuantice fascinante, care necesită cercetări fundamentale și applicate extinse.

The magnetic properties of the nano-width bicrystal interfaces (CIs) of Bi, Sb and 3D topological insulator Bi1xSbx (0.06 ≤ x ≤ 0.2) are studied in a temperature range of 1.6–300 K. These materials do not show superconductivity under normal rhombohedral conditions and are anomalous diamagnetics. At the same time, two superconducting phases with Tc ≤ 21 K and magnetic hysteresis loops against a diamagnetic background typical for strong type II superconductors are identified in Bi interfaces. At the CIs of Bi1xSbx (0.06 ≤ x ≤ 0.2), as well as Sb, a superconducting transition and a ferromagnetic hysteresis loop or a dual loop (superimposed ferromagnetic and superconducting loops) against a paramagnetic background are observed; they indicate the simultaneous occurrence of superconductivity and weak ferromagnetism, which is specific to 3D topological insulators. The revealed coexistence of superconductivity and weak magnetism at these CIs is of significant interest for the fundamental physics and future applications in quantum computing and spintronic devices.Proprietățile magnetice ale interfețelor bicristaline (CIs) de nano-lățime din Bi, Sb și 3D izolator topologic Bi1-xSbx (0,06≤x≤0,2) au fost studiate în intervalul de temperatură 1.6-300K. Aceste materiale nu prezintă supraconductibilitate în condiții romboedrice normale și sunt diamagnetici anormali. În același timp, două faze supraconductoare cu Tc ≤21K și bucle de istereză magnetică pe un fundal diamagnetic tipic pentru superconductorii puternici de tip II au fost identificate în interfețele Bi. În CIs ale Bi1-xSbx (0,06≤x≤0,2), precum și ale Sb s-au observat tranziții supraconductoare și bucle de istereză feromagnetică sau bucle duale (bucle feromagnetice și de tip supraconductor suprapuse) pe un fundal paramagnetic, indicând prezenţa simultană a supraconductivității și feromagnetismului slab, specificâ izolatorilor topologici 3D. Coexistența supraconductivității și a magnetismului slab in aceste CIs manifestă un interes sporit pentru fizica fundamentală și aplicațiile viitoare în computing cuantic și dispozitive spintronice.

Higher order topological insulators (HOTIs) are a new class of topological materials which host protected states at the corners or hinges of a crystal. HOTIs provide an intriguing alternative platform for helical and chiral edge states and Majorana modes, but there are very few known materials in this class. Recent studies have proposed Bi as a potential HOTI, however, its topological classification is not yet well accepted. In this work, we show that the (110) facets of Bi and BiSb alloys can be used to unequivocally establish the topology of these systems. Bi and Bi0.92Sb0.08 (110) films were grown on silicon substrates using molecular beam epitaxy and studied by scanning tunneling spectroscopy. The surfaces manifest rectangular islands which show localized hinge states on three out of the four edges, consistent with the theory for the HOTI phase. This establishes Bi and Bi0.92Sb0.08 as HOTIs, and raises questions about the topological classification of the full family of BixSb1−x alloys. The experimental realization of higher order topological insulator (HOTI) in solid state materials remains elusive. Here, Aggarwal et al. reveal hinge states on three edges of both Bi and Bi0.92Sb0.08 (110) islands, supporting them as a class of HOTI. [ABSTRACT FROM AUTHOR]

We have investigated the growth of BiSbTe3 films by metal organic vapor phase epitaxy on (001) GaAs vicinal substrates. A detailed experimental study of the surface morphologies of BiSbTe3 films grown on GaAs (001) vicinal surfaces was carried out and is discussed in this paper with a view to understanding the step-step interaction kinetics that result in step bunching. BiSbTe3 layers grown on nominal (001) GaAs substrates exhibit triangular facet structures consisting of atomically flat plateau areas separated by steps. In contrast, the growth of films on vicinal substrates was found to result in regular arrays of terrace step structures. The formation of step bunches and rectangular terraces on such film surface is attributed to the preferential incorporation of adatoms at step or kink sites and lateral growth rate anisotropy. [ABSTRACT FROM AUTHOR]

The charge transport properties of the low-dimensional thermoelectric materials K2Bi8-xSbxSe13 (0

The charge transport properties of the low-dimensional thermoelectric materials K2Bi8-xSbxSe13 (02Bi8-xSbxSe13 was analyzed on the basis of the classical semiconductor theory and discussed in the context of recent band calculations. The results suggest that the K2Bi8-xSbxSe13 materials possess coexisting domains with semimetallic and semiconducting characters whose ratio is influenced by the value of x and by local defects. The extent and relative distribution of these domains control the charge transport properties. Electron diffraction experiments performed on samples of K2Bi8-xSbxSe13 with x=1.6 show evidence for such domains by indicating regions with long range ordering of K+/Bi3+ atoms and regions with increased disorder. The semiconducting behavior is enhanced with increasing x (i.e., Sb/Bi ratio) in the composition through a decrease of the semimetallic fraction. [ABSTRACT FROM AUTHOR]

Coevaporated bismuth-tellurium and antimony-tellurium films were fabricated under various deposition conditions (controlled evaporation rates of individual species, substrate temperature, and substrate material), and their thermoelectric (TE) properties (Seebeck coefficient, electrical resistivity, and carrier concentration) were measured in search of optimal TE performance. The tellurium atomic concentration was varied from 48% to 74%, the substrate temperature ranged from 130 to 300 °C, and glass, mica, magnesium oxide, and sapphire substrates were used. The chemical composition and crystal structure of the films were recorded (using microprobe and x-ray diffractometer, respectively), analyzed, and compared with available standard Bi2Te3 and Sb2Te3 single-crystal samples. High-performance TE films had tellurium atomic concentration around 60% and were deposited at a substrate temperature between 260 and 270 °C. [ABSTRACT FROM AUTHOR]

An atomic-scale graded structure has been formed previously in a Bi70Sb30 (at. %) alloy that is miscible in all proportions, by sedimentation of substitutional solute atoms under an ultrastrong gravitational field up to 1×106 G at 220–240 °C [T. Mashimo, T. Ikeda, and I. Minato, J. Appl. Phys. 90, 741 (2001)]. In this study, additional megagravity field experiments were performed on the Bi70Sb30 alloy and pure Bi at different temperatures below their melting points, to investigate the change in crystalline state under the ultrastrong gravitational field. For the Bi70Sb30 alloy ultracentrifuged at 191–205 °C, no change in composition was observed, and the grain sizes of the crystals decreased from several millimeters to tens of micrometers, while no distinct change in grain size was observed for the pure Bi ultracentrifuged under the same experimental conditions. The Bi70Sb30 alloy ultracentrifuged at 220–240 °C consisted of two regions with different morphologies–fine-grained crystals with grain sizes in the range of tens of micrometers in the low gravity region, and large crystals with grain sizes several millimeters long and hundreds of micrometers wide along the direction of gravity in the high gravity region, where sedimentation of atoms was confirmed. The large crystals with hexagonal structures were formed by preferential crystal growth roughly along the c axes, and a large strain that increased as the gravitational field increased existed inside these crystals. Formation of this anomalous crystal state might be correlated with the sedimentation of atoms. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract Bismuth antimony telluride based thermoelectric (TE) materials have been intensively developed and synthesized using different mechanisms, for the room temperature TE applications. In particular, bismuth antimony telluride based TE alloys are very sensitive to deviations in their composition, and to contamination during the materials synthesis. Oxygen contamination during Bi-Sb-Te based materials synthesis is one of the critical factors that alters or diminishes thermoelectric-transport properties. Thus, in this study, how the oxide formation mechanism on the powder surface and bulks of p-type Bi 0.5 Sb 1.5 Te 3 alloys affected the microstructural features and thermoelectric properties were elucidated quantitatively. While applying heat treatment (HT) to Bi 0.5 Sb 1.5 Te 3 powder, the constituent elements interacted with the ambient atmosphere and formed a new oxide phase which acted as a barrier to carrier transport. At the initial stage (300 °C) of heat treatment, only the powder surface was oxidized due to the reaction of outer surface atoms with atmospheric air and moisture. While increasing in temperature during HT, this surface oxygen contamination diffused further inside the powder through the grain boundaries. More diffusion and spreading occurred throughout the matrix at 450 °C. The increment of oxygen content from 0.05 to 0.82 wt% drastically decreased the electrical conductivity by 67%, and thermal conductivity by 7% at the heat treatment temperature of 450 °C. This reduction behavior is mainly due to severe scattering of the carriers/phonons at the new formation of oxide (Sb 2 O 3) phase near grain boundaries and within the matrix. At a glance, a small increase in the oxygen content wouldn't significantly influence the thermoelectric properties; however, at a certain level of oxide formation (0.82 wt%), severe effects could occur due to the intensified scattering or trapping of carriers by the oxide barrier formation at the grain boundaries. Graphical abstract Image 1 Highlights • Determined the oxygen concentration of different heat-treated GA powder and SPS bulks. • Elucidation the relation between the mechanism of oxide formation and the thermoelectric properties of Bi 0.5 Sb 1.5 Te 3 alloys. • Identified Sb 2 O 3 phase at the grain boundary and within the grains. • Demonstrated the thermoelectric performance in Bi 0.5 Sb 1.5 Te 3 alloys with oxygen content. [ABSTRACT FROM AUTHOR]

Many efficient thermoelectric materials belong to the class of topological insulators. Therefore, in recent years considerable efforts have been made to elucidate the influence of nontrivial electronic topology on the thermoelectric properties of thermoelectrics. This review describes the basic transport properties of helical surface states of topological insulators. Their effect on the thermoelectric efficiency of materials is discussed. The main attention is paid to (Bi,Sb)2(Te,Se)3 alloys, which combine the properties of the best thermoelectrics and a model topological insulator. [ABSTRACT FROM AUTHOR]

Li-Bi based liquid metal batteries (LMBs) have attracted interest due to their potential for solving grid scale energy storage problems. In this study, the feasibility of replacing the bismuth cathode with a bismuth-antimony alloy cathode in lithium based LMBs is investigated. The influence of the Bi:Sb ratio on voltage characteristics is evaluated via the constant current discharge method and electrochemical titration. On observing the cross section of the electrode at various stages of discharge, it is determined that both Sb and Bi form solid intermetallics with Li on the cathode. Additionally, the addition of Bi not only reduces the melting temperature of the Bi:Sb intermetallic but also actively contributes to the electrode capacity. Thereafter, a Li|LiCl-LiF|Sb-Bi liquid metal battery with 3 A h nameplate capacity, assembled and cycled at 1 C rate, is found to possess a stable capacity for over 160 cycles. The overall performance of this battery is discussed in the context of cost effectiveness, energy and coulombic efficiencies. [ABSTRACT FROM AUTHOR]

We report on the mechanical and transport properties of polycrystalline bulk BiSb, as a low-temperature thermoelectric material. BiSb samples were prepared by mechanical alloying and hot isostatic pressing, followed by sever plastic deformation (SPD). SPD was applied by either equal channel angular extrusion (ECAE) or non-equal channel angular extrusion (NECAE), at two different temperatures (373 K and 423 K). X-ray diffraction and scanning electron microscopy were used to characterize the prepared samples. The transport properties including the electrical conductivity, Seebeck coefficient and thermal conductivity were investigated, and correlated with the microstructure over the temperature range of 160-360 K. NECAE was found to be more effective than ECAE in enhancing bulk density, grain refinement and preferential grain orientation along the extrusion direction, particularly at higher processing temperatures. This is attributed to the better grain alignment and the creation of more intense grain boundaries and dislocation density, which resulted in an enhancement in carrier mobility and phonon scattering and hence a higher Z value. The highest Z value was achieved via NECAE at 423 K, and had a value of 0.39 × 10 K at 250 K, which is 55% higher than that of the hot-pressed sample, 0.22 × 10 K at 270 K. Also, the micro-hardness of the hot-pressed sample increases by at least 20% by SPD processes. Accordingly, optimized SPD can be classified as an effective processing tool for feasible mass production of bulk BiSb alloy with better thermoelectric performance. [ABSTRACT FROM AUTHOR]

In this work, thermoelectric properties of Bi and Sb atoms substituted PbTe material were predicted by Mott theory through electronic structure calculation. This calculation has been carried by the first-principles DV-Xα molecular orbital method based on Hartree-Fock-Slater approximation. The Pb 14 Te 13 , Pb 13 SbTe 13 and Pb 13 BiTe 13 small clusters with a cubic rocksalt structure ( Fm -3 m ; 225) were designed to be performed PbTe, Pb 0.75 Sb 0.25 Te and Pb 0.75 Bi 0.25 Te materials, respectively. The electronic structure showed that the high symmetry crystal structure, spin energy levels, partial spin density of states and electron charge density. The energy gap and Fermi level have been obtained from energy levels and density of state to be evaluated of electrical conductivity and Seebeck coefficient within Mott's theory predication. [ABSTRACT FROM AUTHOR]

The influence of the annealing temperature from the interval between the solidus and liquidus temperatures of BiSb solid solution on its structure and galvanomagnetic and thermoelectric properties has been studied. It has been shown that films of bismuth-antimony solid solution grown by thermal evaporation in a vacuum will have a large-grained structure after annealing at temperatures higher than the solidus temperature of the solid solution. It has been found that these films offer the lowest resistivity, the highest relative magnetoresistance, and the highest mobility of charge carriers. As the annealing temperature approaches the liquidus temperature, the probability that a dendritic structure will form and antimony-enriched regions will appear grows. This causes an increase in the charge carrier concentration and a decrease in the resistivity with a decrease in the relative magnetoresistance and charge carrier mobility. [ABSTRACT FROM AUTHOR]

In the normal state the 3D topological insulator Bi 1 − x Sb x is diamagnetic and does not show superconductivity because of the extremely low carrier density. Despite this, we have found that the small crystallite disorientation angle (SDA) interfaces of bismuth-antimony bicrystals, which consist of a solitary central part (thickness of about 60 nm) and two similar adjacent layers (∼20 nm) on both sides of it, exhibit two superconducting transitions with critical temperature T c ∼ ( 3.7 – 4.6 ) K and T c ∼ ( 8.3 – 21 ) K , while large crystallite disorientation angle (LDA) interfaces with a higher structural disorder show ferromagnetic hysteresis loops and specific characteristics of a single superconducting layer with a thickness comparable with the entire interface. [ABSTRACT FROM AUTHOR]

In this article, the temperature dependence of electrical resistivity (ρ-T) of Bi20Sb80alloy was investigated by DC four-probe method. The results showed that there were two kinds of liquid–liquid structure transition (L-LST) in liquid Bi20Sb80alloy, one was irreversible at high temperature above the liquids (815–1069°C) and the other was reversible near the melting point (600–720°C). The anomalous points on differential scanning calorimetry curve matched well with that on ρ-T curve which verified the effectiveness of the resistivity experiment. L-LST of high temperature refined the solidification organisation of Bi20Sb80alloy to a certain extent. [ABSTRACT FROM PUBLISHER]

Wide ranging interest in Dirac Hamiltonian is due to the emergence of novel materials, namely, graphene, topological insulators and superconductors, the newly-discovered Weyl semimetals, and still actively-sought after Majorana fermions in real materials. We give a brief review of the relativistic Dirac quantum mechanics and its impact in the developments of modern physics. The quantum band dynamics of Dirac Hamiltonian is crucial in resolving the giant diamagnetism of bismuth and Bi-Sb alloys. Quantitative agreement of the theory with the experiments on Bi-Sb alloys has been achieved, and physically meaningful contributions to the diamagnetism has been identified. We also treat relativistic Dirac fermion as an interband dynamics in uniform magnetic fields. For the interacting Bloch electrons, the role of translation symmetry for calculating the magnetic susceptibility avoids any approximation to second order in the field. The expressions for magnetic susceptibility of dilute nonmagnetic alloys give a firm theoretical foundation of the empirical formulas used in fitting experimental results. The unified treatment of all the above calculations is based on the lattice Weyl-Wigner formulation of discrete phase-space quantum mechanics. For completeness, the magnetic susceptibility of Kondo alloys is also given since Dirac fermions in conduction band and magnetic impurities exhibit Kondo effect. [ABSTRACT FROM AUTHOR]

Narrow bandgap thermoelectric materials based on bismuth-telluride exhibit bipolar conduction that is detrimental to their overall thermoelectric performance. Through fabrication of composites of (Bi,Sb) 2 Te 3 matrix with embedded random colony of (Bi,Sb) 2 Te 3 /Te lamellar (eutectic) with different length scales through a combination of different processing routes such as normal flame melting, cryomilling followed by spark plasma sintering and melt-spinning techniques followed by spark plasma sintering, interfacial charge defects and selective potential barrier were created leading to the injection of excess electron and activation of energy filtering effect of minority carriers. The selective-filtering of charge carriers lead to the delay in the onset of bipolar conduction to a higher temperature as a result of an increase in the band gap. This was found to be responsible for shifting the Peak ZT and the optimum operating regime of our alloys to a higher temperature. Changes in microstructure length scale from normal flame-melting to melt-spinning plus spark plasma sintering resulted in 20% reduction in the total thermal conductivity. [ABSTRACT FROM AUTHOR]

This work presents the template based pulsed potential electrodeposition technique of highly textured single crystalline bismuth antimony telluride (Bi 1-x Sb x ) 2 Te 3 nanowires from a single aqueous electrolyte. Cyclic voltammetry was used as an electroanalytical tool to assess the effect of the precursor concentrations on the composition of the deposits and to determine the deposition potential for each element. Pulsed potential electrodeposition was then applied on a gold-coated anodised alumina template to examine the effect of the pulse parameters on the composition and texture of Bi 27 Sb 28 Te 45 nanowires. The nanowires are cylindrical in shape formed during the deposition inside the porous template and highly textured as they are decorated with sparse distribution of small crystal domains. The electrical conductivity (24.1 × 10 4 S m −1 ) of a single nanowire was measured using a four-point probe technique implemented on a custom fabricated test chip. In this work, we demonstrated that crystal orientation with respect to the transport direction controlled by tuning the pulsed electrodeposition parameters. This allowed us to realise electrical conductivities ∼2.5 times larger than Sb doped bismuth-tellurium based ternary material systems and similar to what is typically seen in binary systems. [ABSTRACT FROM AUTHOR]

Structural, thermal, resistive and magnetic properties of melt quenched Bi 0.88 Sb 0.12 alloys are reported. The samples are heated at three different temperatures, followed by rapid quenching in liquid nitrogen. Large temperature difference between liquidus and solidus lines, led to microscopic in-homogeneity in the alloy. The effect of quenching from different temperatures in polycrystalline Bi 0.88 Sb 0.12 alloy has been studied. The parameters such as strain, unit cell volume, and resistivity are found to increase with temperature. Thermal variation of resistivity depicts non-monotonic temperature dependence. The total negative susceptibility increases and band gap of semiconducting Bi 0.88 Sb 0.12 samples decreases with increasing temperature. [ABSTRACT FROM AUTHOR]

In this work the mechanism and kinetics of crystallization of the Ge2Sb2Te5+Bi thin films were investigated using differential scanning calorimetry. Ge2Sb2Te5 with different amounts of Bi (0, 0.2, 0.5, 0.8, 1, 3, 5 wt.%) was synthesized using quenching technique. Thin films were prepared by thermal evaporation of synthesized materials. X-ray diffraction has shown that synthesized materials had trigonal modification of Ge2Sb2Te5. Introduction of Bi led to the appearance of trigonal modification of Bi2Ge2Te5, which indicates on the replacement of Sb by Bi. As-deposited thin films were amorphous up to 3% of Bi. Higher concentrations of Bi led to the appearance of crystalline phases. Composition of thin films was verified by Rutherford backscattering, and was found to be close to that of the synthesized materials. The joint application of model-free Ozawa-Flynn-Wall and model-fitting Coates-Redfern methods allowed to estimate kinetic triplet for crystallization process of GST225+Bi thin films, and to predict data processing and storage times of the phase change memory cells. It was shown that GST225+0.5 wt.% Bi thin films have the most promising kinetic characteristics among the investigated materials, due to the predicted smallest data processing and largest storage times. [ABSTRACT FROM AUTHOR]

The magnetic-field dependence of the thermoelectric properties and dimensionless figure of merit ( ZT) of a sintered BiSb alloy were experimentally and theoretically evaluated. The Bi-Sb alloy was synthesized in a quartz ampule using the melting method, and the resultant ingot was then ground via ball milling. A sintered BiSb alloy with a particle size in the range of several to several tens of micrometers was prepared using the spark plasma sintering (SPS) method. The magnetic-field dependence of the electrical resistivity, Seebeck coefficient, and thermal conductivity were experimentally evaluated at temperatures of 77-300 K for magnetic fields of up to 2.9 T. The results showed that ZT increased by 37% at 300 K under a 2.5-T magnetic field. A theoretical calculation of the magneto-Seebeck coefficient based on the Boltzmann equation with a relaxation time approximation was also performed. Hence, the experimental result for the magneto-Seebeck coefficient of the BiSb alloy at 300 K was qualitatively and quantitatively explained. Specifically, the carrier scattering mechanism was shown to be acoustic phonon potential scattering and the carrier mobility ratio between the L- and T-points was found to be 3.3, which corresponds to the characteristics of a single crystal. It was concluded that the effect of the magnetic field on the Seebeck coefficient was demonstrated accurately using the theoretical calculation model. [ABSTRACT FROM AUTHOR]

Functionally graded thermoelectric materials (FGTMs) have been prepared by sedimentation of atoms under a strong gravitational field. Starting samples of BiSb alloys with different composition x were synthesized by melting of metals and subsequent annealing of quenched samples. The thermoelectric properties (Seebeck coefficient, electrical conductivity) of the starting materials were characterized over the temperature range from 300 K to 525 K. Strong gravity experiments were performed in a unique ultracentrifuge apparatus under acceleration of over 0.5 × 10 G at temperatures of 538 K and 623 K. Changes of the microstructure and chemical composition were analyzed using scanning electron microscopy with energy-dispersive x-ray spectroscopy analysis. The distribution of the Seebeck coefficient of the Bi-Sb alloys was characterized by scanning thermoelectric microprobe. As a result of sedimentation, large changes in chemical composition ( x = 0.45 to 1) were obtained. It was found that the changes in chemical composition were correlated with alterations of the Seebeck coefficient. The obtained experimental data allowed the development of a semiempirical model for the selection of optimal processing parameters for preparation of Bi-Sb alloys with required thermoelectric properties. [ABSTRACT FROM AUTHOR]

This study investigated the microstructural stability of Bi-Sb20 alloy under the influence of liquid structural transition combined with repeated melting. Liquid structural transition rendered the solidified microstructure dendritic regardless of the number of times the alloy was remelted, whereas the morphology of grains solidified from the original melt changed from equiaxed crystal to dendrite as the number of recycling times increased. Liquid structural transition improved the crystalline quality of the Bi-Sb alloy and decreased the strain in the lattice. Moreover, the microhardness of the samples after liquid structural transition remained steady at approximately 520 MPa for the different recycling times, while it obviously increased with the recycling times before liquid structural transition. These observations indicated that the microstructural stability and Vickers microhardness of the Bi-Sb20 alloy can be controlled through liquid structural transition. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) Dirac semimetals are new quantum materials and can be viewed as 3D analogues of graphene. Many fascinating electronic properties have been proposed and realized in 3D Dirac semimetals, which demonstrate their potential applications in next generation quantum devices. Bismuth-antimony Bi1-x Sbx can be tuned from a topological insulator to a band insulator through a quantum critical point at x≈4%, where 3D Dirac fermions appear. Here, we report on a magnetotransport study of Bi1-x Sbx at such a quantum critical point. An unusual magnetic-field induced semimetal-semiconductor phase transition was observed in the Bi0.96Sb0.04 single crystals. In a magnetic field of 8T, Bi0.96Sb0.04 single crystals show giant magnetoresistances of up to 6000% at low-temperature, 5K, and 300% at room-temperature, 300K. The observed magnetoresistances keep linear down to approximate zero-field when the temperature is below 200K. Our experimental results are not only interesting for the fundamental physics of 3D Dirac semimetals but also for potential applications of 3D Dirac semimetals in magnetoelectronic devices. [ABSTRACT FROM AUTHOR]

Flash evaporation is used to grow BiSbTe films 1200 nm thick on mica substrates. The average lateral crystallite sizes in the as-grown films are ~800 nm. The (0001) plane in the crystallites is preferentially parallel to the substrate plane. After heat treatment in an argon atmosphere, the effective lateral size of crystallites in which the third-order axis is perpendicular to the substrate plane increased by a factor of 3-5. The crystallites were preferentially oriented in the substrate plane as well. The thermoelectric-power parameter of BiSbTe films after their heat treatment in an inert environment increased approximately twofold to values close to that of the corresponding single crystals. [ABSTRACT FROM AUTHOR]

The property anisotropy in BiSeTe alloy is analyzed by constructing index surfaces for the thermoelectric figure of merit and thermal expansion coefficient. Texture is an important factor forming the property anisotropy and technological applicability of an ingot for fabricating modules. The property anisotropy is analyzed based on studying the texture in ingots produced by the modified Bridgman method (thermoelectric plate growth in a flat cavity). Analysis of the texture shows that not only the crystallization rate, but also the crystallization cavity design is an important factor for the proposed crystallization method, affecting the formation of the thermoelectric-material structure. As the plate thickness is decreased by changing the heat removal conditions in a thin gap, a more perfect structure can be obtained. [ABSTRACT FROM AUTHOR]

The structure, composition homogeneity, and electrical properties of bismuth-antimony films with an antimony content below 15 at % prepared by the method of zone recrystallization under a coating on mica and polyimide substrates have been experimentally analyzed; the results are compared with data on block films of a corresponding composition. It is established that the method used makes it possible to prepare single-crystal (single-block) films of BiSb solid solution on substrates with different structures. The films obtained exhibit no inhomogeneities in the antimony distribution over a film volume. Single-crystal films have a much higher relative magnetoresistance than do block films of the same composition prepared by thermal depositions. [ABSTRACT FROM AUTHOR]

The performance of a calcium-antimony (Ca-Sb) alloy serving as the positive electrode in a Ca||Sb liquid metal battery was investigated in an electrochemical cell, Ca(in Bi) | LiCl-NaCl-CaCl2 | Ca(in Sb). The equilibrium potential of the Ca-Sb electrode was found to lie on the interval, 1.2-0.95 V versus Ca, in good agreement with electromotive force (emf) measurements in the literature. During both alloying and dealloying of Ca at the Sb electrode, the charge transfer and mass transport at the interface are facile enough that the electrode potential varies linearly from 0.95 to 0.75 V vs Ca(s) as current density varies from 50 to 500 mA cm-2. The discharge capacity of the Ca||Sb cells increases as the operating temperature increases due to the higher solubility and diffusivity of Ca in Sb. The cell was successfully cycled with high coulombic efficiency (~100%) and small fade rate (<0.01% cycle-1). These data combined with the favorable costs of these metals and salts make the Ca||Sb liquid metal battery attractive for grid-scale energy storage. [ABSTRACT FROM AUTHOR]

The properties of molecular beam epitaxy-grown InSb 1- x Bi x alloys are investigated. Rutherford backscattering spectrometry shows that the Bi content increases from 0.6% for growth at 350°C to 2.4% at 200°C. X-ray diffraction indicates Bi-induced lattice dilation and suggests a zinc-blende InBi lattice parameter of 6.626Å. Scanning electron microscopy reveals surface InSbBi nanostructures on the InSbBi films for the lowest growth temperatures, Bi droplets at intermediate temperatures, and smooth surfaces for the highest temperature. The room temperature optical absorption edge was found to change from 172meV (7.2μm) for InSb to ~88meV (14.1μm) for InSb0.976Bi0.024, a reduction of ~35meV/%Bi. [ABSTRACT FROM AUTHOR]

We have studied the influence of a longitudinal graded inhomogeneity in crystals of bismuth-antimony solid solutions on their effective magnetoresistance, which is one of the parameters determining the efficiency (thermoelectric figure of merit) of a thermoelement operating in the presence of a transverse magnetic field. It is shown that, in a thermoelement operating under the action of an external magnetic field, the negative effect of the crystal inhomogeneity caused by the temperature gradient can be compensated for by its graded composition so as to provide for an increase in the thermoelectric figure of merit of the thermoelement. [ABSTRACT FROM AUTHOR]

The atomic and electronic structures of Bi-rich $${Bi_{1 - x} Sb_{x}}$$ alloys are investigated via ab initio simulation methods. The structural parameters in terms of rhombohedral and hexagonal lattice description as well as density of states (DOS) characteristics as a function of concentration are presented. We show that nonlinearities in the lattice parameters are directly correlated with anomalous transport behavior in available experiments at concentrations less than 5%. The orbital and site projected DOS enable the analysis of relevant contributions from the different atoms. Our calculations also show that the spin-orbit coupling is crucial for the properties of these alloys. [ABSTRACT FROM AUTHOR]

The tunability of the chemical potential for a wide range encompassing the Dirac point is important for many future devices based on topological insulators. Here, we report a method to fabricate highly efficient top gates on epitaxially grown (Bi1-xSbx)2Te3 topological insulator thin films without degrading the film quality. By combining an in situ deposited Al2O3 capping layer and a SiNx dielectric layer deposited at low temperature, we were able to protect the films from degradation during the fabrication processes. We demonstrate that by using this top gate, the carriers in the top surface can be efficiently tuned from n- to p-type. We also show that magnetotransport properties give evidence for decoupled transport through top and bottom surfaces for the entire range of gate voltage, which is only possible in truly bulk-insulating samples. [ABSTRACT FROM AUTHOR]

BiSbPb ( x = 0, 0.5, 1, 2, 3) alloys have been prepared by the mechanical alloying-spark plasma sintering (MA-SPS) method. X-ray diffraction and scanning electron microscopy were used to characterize the microstructure of the alloys. The effect of Pb content on the thermoelectric properties was investigated in the temperature range 77-300 K. The results showed that the electrical transport properties of the Bi-Sb alloys changed from n-type to p-type with substitution of Sb by Pb. The maximum power factor reached 1.6 × 10 W/mK at 190 K, a significant improvement on values reported elsewhere. This study demonstrated that high-performance p-type thermoelectric Bi-Sb materials can be obtained by spark plasma sintering. [ABSTRACT FROM AUTHOR]

Abstract: The magnetic properties of bi-, tri- and multicrystals of 3D topological insulator were studied in the temperature range 1.6–300 K and fields up to 70 kOe using an SQUID magnetometer. Two superconducting phases associated with adjacent and central layers of the crystallite interfaces of the bicrystals are identified. It has been found that due to the different stress structure the transition temperature for one superconducting phase changes considerably, from 8.3 to 36 K, while for another superconducting phase, remains within the range 3.7–4.6 K. In tricrystals and bicrystals with high contents of structural disorder and topological defects, ferromagnetic hysteresis loops and magnetic field expulsion have been observed simultaneously. [Copyright &y& Elsevier]

The electronic structure and thermoelectric properties of (Bi1-xSbx)Te3 compound are investigated by using full-potential linearized augmented plane-wave method and semiclassical Boltzmann theory. The density of states and band structure are studied in detail. The transport coefficients are then calculated with the assumption of the constant relaxation time approximation. We investigated the thermoelectric properties at full range of Sb compositions from x = 0 to x = 1. By using the calculated thermoelectric properties and an averaged thermal conductivity, the figure of merit ZT is obtained. The theoretical investigations show a good agreement with the present experimental data. [ABSTRACT FROM AUTHOR]

Abstract: The sound velocity in selected liquid alloys of the isomorphous Bi–Sb system was measured as a function of temperature with accuracy of ±0.2%. The sound velocity temperature coefficient, dlnc/dT, at the liquidus is found to vary non-monotonously as a function of alloy composition, with the transition from normal to anomalous temperature dependence occurring at a composition of approximately Bi35Sb65. Beyond this composition up to approximately Bi10Sb90, the sound velocity is found to be temperature independent over a wide range. The deviation of the sound velocity from that expected in an ideal solution is found to be dominated by a sub-regular interaction. The present measurements allow the determination of the pressure dependence of the sub-regular solution interaction parameters and are found to be consistent with high pressure studies of the phase diagram in this system. The sound velocity is shown to be an effective measure of the pressure dependence of the alloy interactions. [Copyright &y& Elsevier]

Abstract: Bismuth-based nanostructures have attracted growing interest because of their promising thermoelectric properties and applications in optics and electronics. Pulsed sonoelectrochemical technique was selected to fabricate bismuth–antimony (BiSb) flake-like alloy in ethylene glycol aqueous solution. The formation mechanism for the BiSb alloy was discussed. Ultrasonic played an important role in regenerating electrode and promoting the formation of BiSb nanoflakes. Citrate and polyvinylpyrrolidone (PVP) were introduced as mixed controlling agents during the nucleation and growth process. [Copyright &y& Elsevier]

Abstract: In this work, a bismuth–antimony film electrode (Bi–SbFE) is reported for the first time as a possible alternative for electrochemical stripping analysis of trace heavy metals. The Bi–SbFE was prepared in situ on a glassy carbon electrode and employed in combination with square wave anodic stripping voltammetry in hydrochloric acid solution (pH 2.0). Several key operational parameters influencing the electroanalytical response of Bi–SbFE were optimized, such as the different proportions of Sb(III) and Bi(III), pH value of the measure solution, deposition potential and deposition time. Compared with the bismuth-film electrode (BiFE) and antimony-film electrode (SbFE), the Bi–SbFE displayed higher stripping current response. Under the optimum conditions, the sensor revealed highly linear behavior in the examined concentration range from 1.0 to 220.0μgL−1, with the detection limit of 0.15μgL−1 for Cd(II), offering good reproducibility. The method was applied to the analysis of Cd(II) in tap water sample with satisfactory results. [Copyright &y& Elsevier]

The magnetic susceptibility (χ) of crystals of (BiSb)Te (0 < x < 1) solid solutions has been measured at temperatures from 2 to 400 K. The χ of the crystals containing 10 and 25 mol % SbTe increases with temperature in the range 50 to 220 K, where the Hall coefficient of BiTe increases anomalously. The increase in diamagnetic susceptibility and Hall coefficient with temperature is shown to be caused by a reduction in light-hole concentration, accompanied by a decrease in light-hole effective mass. With increasing SbTe content, the shape of the χ( T) curve changes as a consequence of changes in band structure, which increase the influence of heavy, paramagnetic holes. [ABSTRACT FROM AUTHOR]

pplication of a magnetic field greatly enhances the thermoelectric efficiency of bismuth-antimony (Bi-Sb) alloys. We synthesized a hybrid of Bi-Sb alloy and magnetic nanoparticles, expecting improvement of the thermoelectric performance due to the magnetic field generated by the nanoparticles. Powder x-ray diffraction and magnetic measurements of the synthesized hybrid BiSb(FeSb) sample indicated that the ferromagnetic FeSb nanoparticles, with a size of about 30 nm, were distributed in the main phase of the Bi-Sb alloy. The FeSb nanoparticles act as soft ferromagnets in the diamagnetic host Bi-Sb alloy. The electrical resistivity ρ of the host BiSb sample decreased concomitantly with decreasing temperature, showing a shoulder at 80 K. In contrast, ρ for the hybrid sample was enhanced below 100 K because of carrier scattering by the nanoparticles. The temperature dependence of the Seebeck coefficient S was also altered by the nanoparticle addition. In contrast, the addition of magnetic nanoparticles only slightly influenced the thermal conductivity κ. These results indicate that the addition of magnetic nanoparticles to thermoelectric materials modulates the electronic structures but does not influence the lattice system. [ABSTRACT FROM AUTHOR]

The thermoelectric (TE) performance of BiSbTe polycrystalline alloys has been improved by a simple hot-forging process. No obvious texture was observed in the x-ray diffraction (XRD) patterns of the hot-forged samples. Transport property measurements indicated that the hot-forged samples possessed extremely low thermal conductivities. A maximum ZT value of ∼1.1 at room temperature was obtained for the sample forged under 30 MPa pressure, being almost 50% more than that of the initial unforged alloy. High-resolution transmission electron microscopy (HRTEM) observations suggested that the high density of lattice defects of the hot-forged samples could be responsible for the extremely low thermal conductivities. [ABSTRACT FROM AUTHOR]

Abstract: Directional unsteady-state solidification experiments were performed with hypermonotectic Al–5.0wt%Bi and 7.0wt%Bi alloys. Thermal parameters such as the growth rate (v) and the thermal gradient (G) were experimentally determined by cooling curves recorded along the casting length. The predominant Bi-rich phase was characterized by droplets embedded in the aluminum matrix. Both the interphase spacing (λ) and the Bi-rich particles diameter (d) were measured along the casting length. These microstructural features were correlated to the solidification thermal parameters: growth rate, cooling rate and thermal gradient. An experimental law expressing λ as a function of both G and v was found to better represent the growth of hypermonotectic Al–Bi alloys. Moreover, it was found that the interphase spacing decreases with increasing alloy bismuth content. [Copyright &y& Elsevier]

High-quality films of bismuth antimony telluride were synthesized by electrodeposition from nitric acid electroplating baths. The influence of a surfactant, sodium ligninsulfonate, on the structure, morphology, stoichiometry, and homogeneity of the deposited films has been investigated. It was found that addition of this particular surfactant significantly improved the microstructural properties as well as homogeneity of the films with a significant improvement in the thermoelectric properties over those deposited in the absence of surfactant. A detailed microprobe analysis of the deposited films yielded a stoichiometric composition of Bi0.35Sb1.33Te3for the films electrodeposited in the absence of surfactant and a stoichiometry of Bi0.32Sb1.33Te3for films deposited in the presence of surfactant. [ABSTRACT FROM AUTHOR]