Excess Sb Research Articles

Electronic Properties as a Function of Ag/Sb Ratio in Ag1−y Pb18Sb1+z Te20 Compounds

In this study efforts have been made to optimize the electronic properties such as the electrical conductivity and Seebeck coefficient of Ag1−yPb18Sb1+zTe20 (lead-antimony-silver-tellurium, LAST-18) compounds by systematically varying the Ag and Sb compositions with constant Pb/Te ratio. It was found that increasing the content of Sb relative to Ag raised the charge carrier density (n) and thereby the electrical conductivity and power factor. The results indicate that, for deficient Ag, the excess trivalent Sb atoms occupy divalent Pb sites in the unit cell, increasing the value of n in the system. It was established that the Seebeck coefficient decreases with increasing n, indicating a dominant acoustic phonon scattering mechanism in the current alloys. The results demonstrate that the interaction between Ag and Sb atoms plays a major role in determining the electronic properties in the current Ag1−yPb18Sb1+zTe20 compounds.

Effects of Excess Sb on Thermoelectric Properties of Barium and Indium Double-Filled Iron-Based p-Type Skutterudite Materials

A series of Ba and In double-filled iron-based p-type skutterudite thermoelectric (TE) materials with nominal composition BaInFe3.7Co0.3Sb12+m (0.72 ≤ m ≤ 2.4) have been prepared by melting, quenching, annealing, and spark plasma sintering (SPS) methods. The effects of excess Sb on the phase composition, microstructure, and TE transport properties of these materials were investigated in this work. All the SPS bulk materials are composed of the main skutterudite phase and trace InSb and FeSb2. The content of FeSb2 in the SPS bulk materials gradually decreased and that of InSb remained nearly invariable with increasing m. The impurities InSb and metallic Sb are found at grain boundaries. The amount of metallic Sb at grain boundaries gradually increased with increasing m. The excess Sb had no effect on the growth of grains. The dependence of the TE properties on m indicates that preventing the formation of FeSb2 by adjusting the excess Sb value may significantly improve the TE properties of Ba and In double-filled iron-based p-type skutterudite materials. The significant increases in the carrier concentration and electrical conductivity as well as the remarkable reduction in the lattice thermal conductivity of the sample with m = 0.96 are due to the significant reduction in the FeSb2 content induced by the excess Sb. The gradual increase in ZT with increasing m from 0.72 to 1.44 is attributed to the gradual decrease of the FeSb2 content, and the gradual decrease in ZT in the m range of 1.44 to 2.4 is due to the gradual increase of the Sb content in the Sb-In alloy impurity occurring at grain boundaries. The lowest lattice thermal conductivity of 0.31 W m−1 K−1 and the highest ZT value of 0.63 were obtained at 800 K for the sample with m = 1.44.

Effects of Sb content on microstructure and mechanical properties of Mg-6Zn-Y-Zr- xSb alloy

Effects of Sb content on microstructure and mechanical properties of Mg-6Zn-Y-Zr- xSb alloy were investigated by OM, SEM, XRD and mechanical property test. The results indicate that addition of Sb can break continuous network structure into particles in the interdendritic spaces, and with increasing Sb content, the volume fraction of these particles increases. The as-cast microstructure of the alloy with low content of Sb consists of α-Mg, Zn-rich phase, eutectic structure (α-Mg+ I-phase) and YSb. With increasing Sb content, Mg 3Sb 2 and Mg 4Zn 7 phases appear, while I-phase disappears finally. The ultimate tensile strength and elongation increase first with the increase of Sb content, while the mechanical properties reduce at excessive Sb content.

Nanostructures and defects in nonequilibrium-synthesized filled skutterudite CeFe4Sb12

Abstract

The Role of Si and Sb in the Si-Sb-Te Phase-change Material

ABSTRACTSb-rich Si-Sb-Te phase change materials with different Si contents were proposed and fabricated, and the role of Si and Sb in the Si-Sb-Te alloys was discussed. The resistance-temperature and retention properties of the Sb-rich Si-Sb-Te alloys were studied. Devices based on the Sb-rich Si-Sb-Te alloys were fabricated by a 0.18 μm CMOS technology and device properties were studied by pulsed mode resistance-voltage (R-V) measurements. Experimental results show that the crystallization temperature and data retention ability of the Sb-rich Si-Sb-Te alloys were obviously improved with increasing Si content, but the electrical properties degenerate if too much Si was added. Sb is helpful to promote the crystallization process, but excessive Sb decreases the thermal stability. So, in order to obtain practicable Sb-rich Si-Sb-Te phase change materials, suitable Si and Sb contents are required to balance the device performances between electrical switching property and thermal stability or data retention ability.

Effect of Sb on microstructure and mechanical properties of Mg 2Si/Al-Si composites

The effect of Sb on the microstructure and mechanical properties of Mg 2Si/Al-Si composites was investigated. The results show that Sb can improve the microstructure and mechanical properties of Mg 2Si/Al-Si composites. When the content of Sb is 0.4%, the morphology of primary Mg 2Si changes from dendrites to fine particles, the average size of Mg 2Si particles is refined from 52 to 25 μm, and the ultimate tensile strength and elongation of the composites increase from 102.1 MPa and 0.26% to 138.6 MPa and 0.36%, respectively. The strengthening mechanism can be attributed to the fine-grain strengthening. However, excessive Sb is disadvantageous to the modification of the composites.

Synthesis, structure, magnetic and transport properties of LnFeSb3 (Ln = Pr, Nd, Sm, Gd, and Tb) – tuning of anisotropic long-range magnetic order as a function of Ln

Single crystals of LnFeSb(3) (Ln = Pr, Nd, Sm, Gd, and Tb) have been grown from excess Sb flux. The crystal structure consists of (infinity)(2)[FeSb(2)] octahedra separated by layers of Ln atoms and nearly square planar nets of (infinity)(2)[Sb(2)]. These compounds are metallic and display anisotropic magnetic properties. Long-range antiferromagnetic order is observed in the Sm, Gd, and Tb samples when the magnetic field is applied along the crystallographic a-axis. Evidence of magnetic ordering in all the samples is observed for the field applied parallel to the layers. The magnetic properties are well-described by considering only the magnetic interactions between the Ln 4f moments, with no contribution from the Fe sublattice. Herein, we report the crystal growth, structure, magnetization, transport, and chemical stabilities of the title compounds.

Understanding Electrical Transport and the Large Power Factor Enhancements in Co-Nanostructured PbTe

AbstractWe previously reported the synthesis of nanostructured composite PbTe with excess Pb and Sb metal inclusions. The electrical conductivity shows an unusual temperature dependence that depends on the inclusion Pb/Sb ratio, resulting in marked enhancements in power factor and ZT at 700 K. Additional investigation of the transport and structure of these materials is reported here. Measurements of the scattering parameter reveals there is little change in electron scattering with respect to pure PbTe. High resolution electron microscopy was used to determine additional information about the nature of the precipitate phases present in the samples. High temperature transmission electron microscopy reveals that the precipitates begin to dissolve at high temperatures and completely disappear at T > 619K. A qualitative explanation of the unusual transport behavior of these materials is presented.

High-temperature growth of heteroepitaxial InSb films on Si(1 1 1) substrate via the InSb bi-layer

To achieve the high-temperature growth of heteroepitaxial InSb films on the InSb bi-layer, we studied the influence of substrate temperature of first layer deposition (Ts1) on the two-step growth procedure. Although the growth at higher Ts1 of 240 and 280 °C is difficult to achieve using the usual procedure due to the desorption of In atoms from the InSb bi-layer, it can be realized by means of the adsorption of excess Sb atoms onto an initial InSb bi-layer prepared via √7×√3-In surface reconstruction. The high-temperature growth of 30°-rotated InSb films at 420 °C was demonstrated on a Si(1 1 1) substrate with a InSb bi-layer. The electron mobility of the InSb film grown at 420 °C was about 20,000 cm 2/V s at RT.

Effects of excess Sb on crystallization of δ‐phase SbTe binary thin films

AbstractThe phase‐change temperature and crystal structures of the δ‐phase SbTe alloy for Sb contents of 64 at%, 72 at%, and 76 at% have been investigated. The δ‐phase SbTe alloy has a rhombohedral crystal structure, and crystallization occurs in an extremely narrow temperature range of 140–145 °C compared with Sb40Te60. We have determined the relationship between the Sb content and the crystalline structure using X‐ray diffraction and selected area electron diffraction. When the Sb content increases, the number of Sb layers stacked with Sb2Te3 in the unit cell increases, which results in the lowering of the activation energy for crystallization and a lower ovonic threshold voltage. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Electrical Characterization of Nonvolatile Phase-Change Memory Devices Using Sb-Rich Ge–Sb–Te Alloy Films

We modified the composition of Ge–Sb–Te alloys for phase-change-type nonvolatile memory devices to realize more reliable memory operations. It is expected that the stability of the low-resistance crystalline phase of the Ge–Sb–Te alloy can be improved when an appropriate amount of excess Sb is added to conventional stoichiometric Ge2Sb2Te5 (GST), because a phase transition directly occurs from the amorphous phase to the more conductive hcp phase without the formation of the less conductive metastable fcc phase. Phase-change memory devices using Sb-rich Ge–Sb–Te alloys were fabricated, where the Sb atomic ratio was controlled to be from 31 to 47%. The effect of Sb addition to GST on the phase-change switching characteristics was investigated in terms of the electrical behaviors of the fabricated memory devices. For the set operations, the threshold voltage (Vth) for electronic switching and the required current for set were observed to decrease with increasing Sb composition. The data endurance of memory devices under repetitive operations was measured to be in the range from 1×105 to 2×106 cycles. From the investigations using energy dispersive X-ray spectroscopy (EDS), it was clearly shown that there was no phase separation and/or marked compositional change of the device experiencing 2×106 successive operations, when the Sb atomic ratio in the Ge–Sb–Te alloy was 39%.

Effects of Sb compensation on microstructure, thermoelectric properties and point defect of CoSb3 compound

Volatilization of Sb during the fabrication of CoSb3 by mechanical alloying and then spark plasma sintering has been successfully compensated by adding excess Sb. The average grain size increases apparently with excess Sb content, abnormally grown by about 100 times as the excess Sb is up to 4 at.%. A liquid-phase-related mechanism is used to explain the abnormal growth. The uncompensated sample shows a negative Seebeck coefficient near room temperature, while the sample compensated with 6 at.% excess Sb shows an intrinsic positive Seebeck coefficient and an enhanced ZT value, which has a maximum of about 0.1 at 350 °C, which is two times higher than the uncompensated one. The transition of electrical conductivity from n- to p-type relative to the Sb compensation is discussed in relation to the point defect. A defect equation is given to show the nature of electron generation due to Sb deficiency. The Sb-vacancy not only provides extrinsic carrier but also generates a significant impact on the band gap and hence on the Seebeck coefficient.

Thermoelectric properties of nanostructured (Pb1-mSnmTe)1-x(PbS)x with Pb and Sb precipitates

AbstractWe report the physical characterization and thermoelectric properties of (Pb0.95Sn0.05Te)0.92(PbS)0.08 containing excess Pb and Sb prepared using the matrix encapsulation technique. Samples of (Pb0.95Sn0.05Te)0.92(PbS)0.08 : Pb 0.5 - 4 at. % rapidly quenched from the melt show microscale Pb inclusions that increase the thermal conductivity while slightly increasing the power factor, compared to (Pb0.95Sn0.05Te)0.92(PbS)0.08. Samples of (Pb0.95Sn0.05Te)0.92(PbS)0.08 : Pb 0.5%, Sb 2% prepared using the same technique show microscale Sb and Pb inclusions that upon heating cause rapid PbS and Sb segregation from the PbTe matrix. This behavior significantly alters the microstructure and degrades the transport properties of the material.

Transport Behavior and Thermal Conductivity Reduction in the Composite System PbTe-Pb-Sb

AbstractWe report the synthesis of nanostructured composite PbTe with excess Pb and Sb metal inclusions. Scanning and transmission electron microscopy reveal these inclusions in both the nano- and macroscales. The electrical conductivity and Seebeck coefficient dependence on temperature show unusual trends which depend on the inclusion Pb/Sb ratio. Several ratios showed marked enhancements in power factor at 700 K. The thermal conductivity of these composites is reported.

Dynamic Threshold Switching Behavior of Ge[sub 2]Sb[sub 2]Te[sub 5] and Sb-doped Ge[sub 2]Sb[sub 2]Te[sub 5] Thin Films Using Scanning Electrical Nanoprobe

The dynamic oscillation in the current-time characteristics of Ge 2 Sb 2 Te 5 and Sb-doped Ge 2 Sb 2 Te 5 thin-film materials was investigated using a scanning electrical nanoprobe. The dynamic oscillation was attributed to the threshold switching of the amorphousphase Ge 2 Sb 2 Te 5 and doped Ge 2 Sb 2 Te 5 thin films. The microscopic mechanism of the threshold switching behavior was also studied. X-ray diffraction showed that the excess Sb improved the crystallization of Ge 2 Sb 2 Te 5 during postannealing at 300°C. Sb-doping also increased the threshold switching speed.

Role of Nb in rutile-type Cr/V/Sb/Nb mixed oxides, catalysts for propane ammoxidation to acrylonitrile

Rutile-type Cr/V/Sb/Nb mixed oxides were prepared by coprecipitation from ethanolic solutions and calcination at 700 °C. They were then tested as catalysts for the gas-phase ammoxidation of propane. The addition of increasing amounts of Nb to the rutile Cr/V antimonate led to a considerable increase in the selectivity to acrylonitrile and to a lower selectivity to N 2 derived from ammonia overoxidation. But this effect was evident only when excess Sb was present with respect to the stoichiometric requirement for the formation of the rutile compound. Evidence was obtained for the development of rutile-type mixed Cr/V antimonate/niobate; this multicomponent rutile had a highly defective structure, with cationic vacancies in relation to excess Sb 5+ with respect to the stoichiometric composition. The progressive increase of Nb concentration in this mixed oxide with increasing Nb loading led to a partial segregation of Sb oxide in the form of Sb 2O 4. The excess Sb in rutile provided the active sites for allylic ammoxidation on intermediate adsorbed propylene. The contemporaneous presence of Nb in the lattice improved the efficiency of these sites and was responsible for the better catalytic performance with respect to the Cr/V/Sb/O systems.

Thermoelectric properties of undoped p-type CoSb 3 prepared by vertical Bridgman crystal growth and spark plasma sintering

A crystal of p-type CoSb 3 was grown using the vertical Bridgman method. In the as-grown condition, polycrystalline CoSb 3 grains surrounded by metallic Sb were obtained. Post-annealing was used to remove the excess Sb because the residual Sb degrades the thermoelectric properties. Subsequent heat treatment at 1073 K for 5 h removed the residual Sb, resulting in the formation of voids in the crystal. For the annealed samples, an increase in the Seebeck coefficient from 40 to 300 μV/K and a decrease in the electrical conductivity were observed. To improve the conductivity, metal was deposited on the surfaces of post-annealed samples. The maximum power factor was 5.1 × 10 −5 W/cm K 2 obtained at 523 K for a post-annealed sample with 100 nm of metal deposited. To understand the effect of voids in the annealed samples, highly condensed CoSb 3 samples were treated with a typical spark plasma sintering (SPS) method using the grown polycrystalline CoSb 3 as starting material. The thermoelectric properties of the SPS samples were compared with those of the post-annealed samples. The 100 nm Au-deposited on the post-annealed samples gave rise to an overall decrease in the value of the thermal conductivity reported previously. The maximum value of the figure of merit obtained was 0.84 at 573 K.

Photoelectrochemical properties and crystalline structure change of Sb-doped TiO2thin films prepared by the sol-gel method

Ti1−XSbXO2samples were obtained from dip-coating sol-gel method and a subsequent anneal at 450 °C. They had an average crystallite size of 13.3–20 nm. Cyclic voltammograms taken under ultraviolet (UV) and Xe lamp illumination in a 0.5 M Na2SO4electrolyte showed that the Sb-doped samples had greater photocurrent densities than pure titania electrode, with an optimal Sb concentration of 0.2%. Oxidative peaks were observed in the cyclic voltammograms obtained in the dark after certain exposure duration to UV light. X-ray diffraction patterns and Raman spectra show a phase transformation from brookite to anatase in the samples with Sb concentration up to 0.2%. Ti4+ions were substituted by Sb to form the anatase structure of Sb–O–Ti, improving the crystallization efficiency. The Sb–Sb bonds were formed due to the introduction of excessive Sb atoms.

Metalorganic Vapor Phase Epitaxy Growth of InAlAsSb on InP

This paper studies the characteristic of InAlAsSb grown on InP substrates by metalorganic vapor phase epitaxy (MOVPE) using trimethylindium (TMI), trimethylaluminum (TMA), trimethylantimony (TMSb) and arsine (AsH3). Composition analyses of InAlAsSb layers grown at various TMSb flow rates show, for the first time, that the Al concentration in the InAlAsSb layer decreases as the TMSb flow rate increases. We also find that the growth rate of InAlAsSb decreases remarkably as the TMSb flow rate increases. To clarify the reasons for these phenomena, the growth rates of the InAsSb and AlAsSb components are estimated. The growth rate of AlAsSb component shows a similar remarkable tendency with the InAlAsSb growth rate but that of InAsSb almost retains. This means that the decomposition of TMA is suppressed by the presence of TMSb. It is shown that excess Sb on the growth surface is related to this suppression.

Effects of post-annealing on thermoelectric properties of p-type CoSb 3 grown by the vertical Bridgman method

Crystals of CoSb 3, a peritectic skutterudite compound, were grown by the vertical Bridgman method at various growth speeds ranging from 0.4 to 2.8 mm/h. Changes in the growth parameters resulted in the formation of polycrystalline p-type CoSb 3 grains surrounded by Sb metal. To remove the excess Sb in the as-grown crystals, post-annealing was performed. Removing the residual Sb through the post-annealing process caused reconstruction of CoSb 3 grain externals and formation of voids in the crystals, resulting in an increase in the Seebeck coefficient from around 40 μV/K (in as-grown samples) to 250–500 μV/K. The increased Seebeck coefficient values of the post-annealed samples are higher than that of single-crystal bulk CoSb 3 with the corresponding carrier concentration.