Sb-rich Regions Research Articles

Assessment of Mixing Properties of Liquid Cu-Sb Alloy at Different Temperatures

The addition of copper (Cu) can decrease the toxicity of the most usable element antimony (Sb). Concentration-dependent thermodynamic, microscopic structural and transport properties of Cu-Sb melt at different temperatures were examined using the quasi-lattice theory of mixing. Moelwyn-Hughes’s approach was implemented for the computation of viscosity. Liquid Cu-Sb shows the segregating nature in the Sb rich region and the ordering nature in the Cu rich region at the temperature range of 1190-1490 K. The viscosity of the respective alloy decreases with an increase in temperature.

Muon-spin relaxation and AC magnetometry study of the ferrimagnet LaSr2Cr2SbO9

AC susceptibility and muon spin relaxation data have been collected from a polycrystalline sample of LaSr2Cr2SbO9, a perovskite-like compound wherein the unequal distribution of Cr3+ and Sb5+ cations over two crystallographically-distinct six-coordinate B sites results in the onset of ferrimagnetism at ~150 K. The data are used to elucidate the dynamics of the ferrimagnetic domain walls, thought to lie in Sb-rich regions, and suggest an energy barrier of ~0.13 eV to their motion. The muon data confirm that the ferrimagnetic order is a true bulk phenomenon. The behaviour of this material is briefly compared to that of Ni2+- based relaxor ferromagnets.

Passivation of Cu–Sb anodes in H2SO4−CuSO4 aqueous solution observed by the channel flow double electrode method and optical microscopy

In the electrorefining of Cu, the precipitation of copper sulfate on the anode surface causes passivation, which decreases current efficiency. Because the presence of Sb in a Cu anode is known to accelerate passivation, this study investigated the anodic behaviors of Cu–Sb alloys in a H2SO4−CuSO4 electrolyte by a direct observation method that combined optical microscopy with the channel flow double electrode technique. When a Cu−Sb (5 wt% Sb) anode (here denoted “Cu−5 wt%Sb”) with Sb segregation was dissolved, the Sb-rich region remained on the surface, inhibiting Cu dissolution and ion transfer and resulting in acceleration of passivation, which was observed as a drastic decrease in current density during voltammetry. However, a Cu−5 wt%Sb anode solutionized by heat treatment showed a moderate decrease in current density in some measurements, indicating prevention of passivation. It was observed that the dissolution of the solutionized Cu−5 wt%Sb anode generated an Sb-rich layer with complex sulfate compounds on its surface and accompanying pits. Copper sulfate precipitated selectively on the Sb-rich layer and grew into coarse grains, without covering the entire anode surface. These results suggest that passivation can be prevented by controlling the microstructure, even when an anode contains Sb. The results of this work are expected to contribute to the development of an efficient electrorefining process of Cu anodes containing high concentrations of Sb.

Al-Sb-Ge phase change material: A candidate for multilevel data storage with high-data retention and fast speed

The phase change memory with Al-Sb-Ge alloy is investigated for the feasibility of embedded system and the potential possibility of multilevel data storage. The Al15Sb53Ge32 compound has a high crystallization temperature (333 °C) and outstanding data retention ability (260 °C). Ge atoms inhibit crystal growth to enhance thermal stability and Al15Sb53Ge32 contains sequential crystallization of Sb-rich and Ge regions in two-step crystallization process. Remarkably, the device presents a fast speed of 50 ns and endurance up to 2.3 × 104 cycles. At the same time, a reliable tripe-level resistance state of the phase change memory cell is observed.

Atom-scale compositional distribution in InAlAsSb-based triple junction solar cells by atom probe tomography

The analysis by atom probe tomography (APT) of InAlAsSb layers with applications in triple junction solar cells (TJSCs) has shown the existence of In- and Sb-rich regions in the material. The composition variation found is not evident from the direct observation of the 3D atomic distribution and because of this a statistical analysis has been required. From previous analysis of these samples, it is shown that the small compositional fluctuations determined have a strong effect on the optical properties of the material and ultimately on the performance of TJSCs.

AgPbmSbTem+2 microspheres comprised of self-assembled nanoparticles driven by inhomogenous co-doping synergetic induced dipoles and their thermoelectric and electrochemical Li-storage properties

Design and fabrication of low-cost, high efficient and robust three-dimensional (3D) microspherical materials for energy conversion and storage is of paramount importance. Here, we first reported a template-free and efficient hydrothermal method to synthesize quaternary AgPb10SbTe12 (AgPbmSbTem+2, m=10) microspheres comprised of tiny nanoparticles driven by co-doping synergetic dipole-driven aggregation. Due to the effect of site blocking, Ag and Sb atoms tend to segregate into Ag-rich and Sb-rich regions, creating substantial inhomogeneity on the nanoscale. Theoretical calculations confirm the dipole-field-driven mechanism forming the microsphere structure. The inhomogeneous local structure has a high impact on the physical properties of the synthesized compounds: the local Ag/Sb ordering and multiple nanoscale interfaces result in the improved thermoelectric performance and cycling stability during the lithiation/delithiation process in Li ion battery compared to their binary or ternary compounds.

P-Type Co Interstitial Defects in Thermoelectric Skutterudite CoSb3 Due to the Breakage of Sb4-Rings

Skutterudite CoSb3 based thermoelectric devices have high potential for engineering applications because both n- and p-type doped CoSb3 demonstrate excellent thermoelectric performance. A crucial point concerning the application of CoSb3 is to understand and control its defect chemistry. To reveal the native conductivity behavior of nonstoichiometric CoSb3, we investigated the intrinsic point defects in CoSb3 using density functional theory. We found CoSb3 is p-type in either Co or Sb rich regions of phase stability. Interstitial Co (Coi) and interstitial Co-pair (Coi-p) are the dominant point defects in the Co rich region. However, Coi-p will be difficult to form because the formation temperature of Coi-p is much lower than the synthesis temperature of CoSb3. The unexpected acceptor nature of the Coi or Coi-p defects is explained by the breakage of multiple Sb4-rings. Co vacancy (Cov) is found to be the p-type defect in the Sb rich region. Furthermore, the solubility of excess Co in CoSb3 is expected to ...

Amorphous structure and bonding chemistry of aluminium antimonide(AlSb)) alloy for phase-change memory device

With the help of first-principles molecular dynamics calculations, we obtained the atomic picture of amorphous AlSb(a-AlSb) for phase-change memory application. Generally, a-AlSb shows sp3 bonding network, which is the intrinsic characteristic for its good thermal stability. Significant wrong(homogenous) Al-Al bonds can also be observed from the pair correlation function. This hints the amorphous phase may consist of Al cluster and Sb-rich Al-Sb alloy. Recent experiment has observed the Sb-rich region of AlSb alloy can be switched to crystal, on the basis of which, combined with our calculations, we thus propose that on the one hand such a Sb-rich region in a-AlSb can retain the rapid crystallization like pure Sb solid and on the other hand some Al atoms play the important role of stabilizing Sb rich network with sp3 bonding. The present study offers a microscopic view to understand the phase change mechanism of AlSb alloy for information storage device.

Effect of annealing in the Sb and In distribution of type II GaAsSb-capped InAs quantum dots

Type II emission optoelectronic devices using GaAsSb strain reduction layers (SRL) over InAs quantum dots (QDs) have aroused great interest. Recent studies have demonstrated an extraordinary increase in photoluminescence (PL) intensity maintaining type II emission after a rapid thermal anneal (RTA), but with an undesirable blueshift. In this work, we have characterized the effect of RTA on InAs/GaAs QDs embedded in a SRL of GaAsSb by transmission electron microscopy (TEM) and finite element simulations. We find that annealing alters both the distribution of Sb in the SRL as well as the exchange of cations (In and Ga) between the QDs and the SRL. First, annealing causes modifications in the capping layer, reducing its thickness but maintaining the maximum Sb content and improving its homogeneity. In addition, the formation of Sb-rich clusters with loop dislocations is noticed, which seems not to be an impediment for an increased PL intensity. Second, RTA produces flatter QDs with larger base diameter and induces a more homogeneous QD height distribution. The Sb is accumulated over the QDs and the RTA enlarges the Sb-rich region, but the Sb contents are very similar. This fact leaves the type II alignment without major changes. Atomic-scale strain analysis of the nanostructures reveal a strong intermixing of In/Ga between the QDs and the capping layer, which is the main responsible mechanism of the PL blueshift. The improvement of the crystalline quality of the capping layer together with higher homogeneity QD sizes could be the origin of the enhancement of the PL emission.

Phase transition characteristics of Al-Sb phase change materials for phase change memory application

The crystallization behavior of Al-Sb thin films is investigated for phase change memory application. The crystallization temperature and optical band gap of the amorphous material increase with Al content. The thermal stability and randomness in atomic configuration of the films are enhanced considerably. The shift of Raman modes associated mainly with Sb upon phase transformation is observed, and the co-existence of Sb-rich crystalline regions and Al-rich amorphous matrix is confirmed, revealing the amorphous nature of most Al components. Three distinct resistance levels are achieved in the devices using Al50Sb50, suggesting the potentiality for multilevel data storage application of the materials.

Impact of N on the atomic-scale Sb distribution in quaternary GaAsSbN-capped InAs quantum dots

The use of GaAsSbN capping layers on InAs/GaAs quantum dots (QDs) has recently been proposed for micro- and optoelectronic applications for their ability to independently tailor electron and hole confinement potentials. However, there is a lack of knowledge about the structural and compositional changes associated with the process of simultaneous Sb and N incorporation. In the present work, we have characterized using transmission electron microscopy techniques the effects of adding N in the GaAsSb/InAs/GaAs QD system. Firstly, strain maps of the regions away from the InAs QDs had revealed a huge reduction of the strain fields with the N incorporation but a higher inhomogeneity, which points to a composition modulation enhancement with the presence of Sb-rich and Sb-poor regions in the range of a few nanometers. On the other hand, the average strain in the QDs and surroundings is also similar in both cases. It could be explained by the accumulation of Sb above the QDs, compensating the tensile strain induced by the N incorporation together with an In-Ga intermixing inhibition. Indeed, compositional maps of column resolution from aberration-corrected Z-contrast images confirmed that the addition of N enhances the preferential deposition of Sb above the InAs QD, giving rise to an undulation of the growth front. As an outcome, the strong redshift in the photoluminescence spectrum of the GaAsSbN sample cannot be attributed only to the N-related reduction of the conduction band offset but also to an enhancement of the effect of Sb on the QD band structure.

High-resolution nanostructural investigation of Zn 4Sb 3 alloys

Zinc antimonides exhibit high thermoelectric figures of merit and bear great potential for power generation. To advance the understanding of the structure–property relationship in these alloys, the microstructure of a nanocrystalline Zn4Sb3 alloy, containing 57.29 at.% Zn, was investigated by scanning electron microscopy and atom probe tomography. Chemical inhomogeneities were observed at grain boundaries. Within the grains the distribution of Zn shows large fluctuations inducing a complex microstructure made of Zn-rich and Sb-rich regions at a nanometer scale.

X-ray diffraction, Raman and photoacoustic studies of InSb nanocrystals

Zinc blend InSb nanocrystals were generated by mechanical alloying and X-ray diffraction, Raman spectroscopy and photoacoustic absorption spectroscopy techniques were used to study its structural, optical and thermal properties. Annealed nanocrystals were also studied. Residual amorphous and minority crystalline (Sb and In 2O 3) phases were also observed for mechanical alloyed and thermal annealed samples, respectively. The structural parameters, phase fractions, average crystallite sizes and microstrains of all crystalline phases found in the samples were obtained from Rietveld analyses of their X-ray diffraction patterns. Raman results for both as-milled and annealed samples show the Raman active LO and TO modes of the zinc blend InSb phase and Sb-rich regions. The photoacoustic results of both samples were satisfactorily explained by thermal bending heat transfer mechanism and an increase on effective thermal diffusivity coefficient was observed after annealing.

Nonuniversality of the non-Fermi-liquid state inCeRhSb1−xSnxcompounds on the Sn-rich side

We examine the electronic properties of the $\mathrm{Ce}\mathrm{Rh}{\mathrm{Sb}}_{1\ensuremath{-}x}{\mathrm{Sn}}_{x}$ metallic series with $0.78\ensuremath{\leqslant}x\ensuremath{\leqslant}1$ by treating the non-Fermi liquid (NFL) state of CeRhSn as a reference state. A nonuniversal behavior of the NFL phase is observed as a function of $x$, which is attributed to enhanced magnetic disorder effects introduced by alloying, from one side and to the role of spin fluctuations due to Rh $4d$ electrons from the other. The NFL behavior at the lowest temperatures is attributed to quantum critical fluctuations among $4f$ electrons due to Ce, whereas the spin fluctuations become pronounced at higher temperatures $Tg6\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Thus, in Sn-rich samples those two types of fluctuations coexist. An itinerant-electron type of spin-glass-like state with a small magnetic moment appears at temperatures $T\ensuremath{\leqslant}5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. These studies complement our previous work on the same system in the Sb-rich region, i.e., with $0\ensuremath{\leqslant}xl0.2$, where the Kondo semiconducting state evolves into NFL state via a quantum critical point located at $x\ensuremath{\cong}0.12$.

Pattern formation in SiSb system

Thermal annealing of Si/Si 1− x Sb x /Si amorphous thin-film tri-layer samples ( x = 18 and 24 at%Sb) under 100 bar Ar pressure results in an interesting pattern formation. In pictures, taken by means of cross-sectional transmission electron microscopy, stripe-shaped contrast, with three maxima, parallel to the interfaces can be seen. Secondary neutral mass spectrometer measurements revealed that the regions with different contrasts correspond to Sb-rich and Sb-depleted regions. Furthermore, the Sb concentration peaks in the Sb-rich regions, especially at longer annealing times, are different: the peak developed at the Si/SiSb interface closer to the free surface decays faster than that of the inner one closer to the substrate. The pattern formation is interpreted by segregation-initiated spinodal-like decomposition, while the difference of the Sb concentration peaks is explained by the resultant Sb transport to and evaporation from the free surface. The possible role of formation of nanocrystalline grains, in the explanation of the fast transport under pressure as compared to vacuum is also discussed.

On the optical properties of thermoelectric alkali metal chalcogenide compounds

ABSTRACTSolid solutions of K2Bi8−XSbXSe13 is an interesting series of complex bismuth-chalcogenide compounds, which are attractive for thermoelectric investigations. The highly anisotropic structure in these compounds results in needle-like morphology along the b- crystallographic axis, leaving structural tunnels where K+ ions reside. The complex electronic structure that arises from a large and low symmetry unit cell and the weakly bound K+ ions, lead to high Seebeck coefficient, highly anisotropic electrical properties and very low thermal conductivity.Reflectivity spectra in the FIR region are presented for several members in the Sb-rich (x≥6) side. Optical investigations are carried out on crystalline and pelletized samples. The received spectra are analyzed, examined comparatively and discussed. Results indicate that upon Bi/Sb substitution in the Sb-rich region, phonons develop a mixed-mode behavior in the FIR spectral region.

Characterisation of erbium–erbium oxide bilayer structures deposited on GaSb substrates by electron beam evaporation

In this work the structure of electron gun thermally evaporated films of Er/Er 2O 3 on Bridgman-grown GaSb substrates has been studied by means of atomic force microscopy and scanning electron microscopy. The microcrystalline structure of the uppermost Er film consists in hexagonal microcrystals, being around 1 μm in size with a surface roughness of about 200 nm for the evaporation conditions used here. In order to characterise the overall composition of this bilayer structure, Rutherford backscattering spectroscopy and secondary ion mass spectrometry analysis have also been carried out. The composition of the different layers could be determined and the analysis has also revealed diffusion processes between the layers and the substrate. The presence of Sb diffused from the substrate has been observed both in the oxide and metal layer and the formation of an Sb-rich region between the substrate and the oxide layer has also been proved. It has also been identified that the presence of a small amount of Er into the substrate and the SIMS spectra have established the metal–oxide–semiconductor nature of the structure.

Lateral composition modulation in mixed anion multilayers

Lateral composition modulation on the group V sublattice has been observed in GaAs/GaSb short period superlattices. Cross sectional transmission electron microscopy and x-ray diffraction reciprocal space maps reveal that all structures are phase-separated with Sb compositions for the strongest modulated structure of x=0.73 in the Sb-rich regions, x=0.55 in the As-rich regions, and wavelengths 15⩽Λ⩽20 nm. The composition modulation observed in these films is not due to spinodal decomposition, because an alloy grown at the same conditions results in a homogeneous layer, but may be related to vertical stacking of quantum dots that nucleate during the growth of the structure.

The antimony-iron-zirconium (Sb-Fe-Zr) system

Phase equilibria were established in the Fe-Sb-Zr ternary system below 60 at.% Sb for an isothermal section at 800 °C; the very Sb-rich region was studied at 600 °C. Investigation of the phase relations was based on light optical microscopy, electron probe microanalysis, and X-ray diffraction experiments on arc melted bulk alloys, which were annealed up to 350 h. Three ternary compounds were observed: ZrFe1−x Sb (0.3<x<0.5; defect TiNiSi Type), Zr6Fe1−x Sb2+x (0<x<0.24; ordered Fe2P type) and Zr5Fe x Sb3−x (x=0.44; W5Si3 type). Whereas Zr5Fe0.44Sb2.56 at 800 °C formed at a given composition without a significant homogeneity region, a rather extended solid solution up to about 9 at.% Sb was observed for the Laves phase Zr(Fe1−x Sb x )2−y . At 800 °C, binary ZrFe2−y was only observed with the cubic MgCu2 type; Sb content of more than about 3 at.% Sb stabilized the hexagonal MgNi2 type in the Zr-poor end of the homogeneity region. The MgCu2 type prevails at higher Sb content of up to 9 at.% Sb at the Zr-rich side. Zr3Sb (Ni3P type) seems to dissolve up to 3.5 at.% of Fe replacing Zr in the structure. Binary Zr5Sb3+x (Ti5Ga4 type or filled Mn5Si3 type) dissolves up to 11 at.% Fe by gradually replacing the Sb atoms in the octahedral sites with Fe; thus the boundary of the homogeneous region on the Fe-rich side essentially corresponds to the ternary limit at Zr5FeSb3. For stoichiometric binary Zr5Sb3 the authors observed only a small solubility (<1 at.% Fe) with the Yb5Sb3 type. At 800 °C there is practically no solid solubility of Zr in the iron antimonides and of Fe in the zirconium antimonides richer than 40 at.% Sb.

Measurement of activity of gallium in liquid Ga–Sb–Sn alloys by emf method with zirconia as solid electrolyte

The emf of galvanic cells with zirconia solid electrolytes was measured to determine the activity of gallium in liquid Ga–Sb–Sn alloys in the 1050–1150 K temperature range along three lines of constant antimony-to-tin mole ratio. A mixture of Ga and Ga 2O 3 was used as a reference electrode. The activity curves of Ga show negative to positive deviations from the ideal behavior with increasing Sn concentrations in the lower concentration range of Ga; whereas in the concentration range X Ga≥0.6, the activity of Ga in the ternary alloys shows positive deviations from the ideal behavior. Isoactivity curves at 1073 K, in the ternary Ga–Sb–Sn alloys, were derived by combining the activity data for Ga–Sb and Ga–Sn alloys. The shape of the curves is simple in the Ga-poor region, but shows a wavy form with increasing Ga concentration. Isovalue curves in the excess free energies of mixing in the ternary alloys are derived by the Darken method. The results are in agreement with values derived by using the Chou method on the Sb-poor side, but the agreement is not good in the Sb-rich region.