Se Alloys Research Articles

ФАЗОВЫЕ РАВНОВЕСИЯ В СИСТЕМЕ Hg–Se ПРИ ВАКУУМНОЙ ДИСТИЛЛЯЦИИ

Abstract. One of the possible ways to recover components from the Hg–Se alloy formed during the processing of copper-electrolyte sludge is vacuum distillation. Object of research: Hg–Se alloys of composition, mol %: 0.01–99.99 Hg; 99.99–0.01 Se, the formation of which is possible during the processing of copper-electrolyte sludge in the production of commercial selenium concentrate. The purpose of the work: calculation of the “gas – liquid” VLE (vapor liquid equilibrium) equilibrium states, including the dependence of the phase composition on temperature (T – x) and pressure (P – x) for the Hg–Se alloy during vacuum distillation. Methods and approaches used. The activity coefficients of the Hg–Se alloy components were calculated using a simplified version of the simple molecular interaction volume model (SMIVM). Phase diagrams of temperature (T – x) and pressure (P – x) are used to pre-select the system temperature and pressure, and to evaluate the efficiency of component separation during vacuum distillation. Novelty: calculation of activity coefficients using a simplified version of the SMIVM model. Main results. In the temperature range of 823‒1073 K, saturated vapor pressures were calculated for Hg (pHg * = 1.418·106‒1.046·107 Pa) and Se (pSe * = 1.42·104‒3,66·105 Pa). High values of the ratio pHg */pSe * = 100.2‒28.6 and the separation coefficient lgβHg = 2.73‒1.01 create theoretical prerequisites for the selective separation of these metals by vacuum distillation, when mercury is enriched in the gas phase (βHg > 1), and selenium – in the liquid phase. The molar fraction of selenium in the gas phase xSe = 0.553–1.43·10‒12 decreases with a decrease in the temperature of 1073‒823 K and the molar fraction of the element in the alloy xSe = 0.99–0.01. For the “liquid – gas” interface of the Hg–Se alloy, the values of changes in the excess Gibbs energy, enthalpy, and entropy are determined ‒ΔGm E = 0.8–3.0 kJ/mol; ‒ΔHm E = 1.86–5.39 KJ/mol; ‒ΔSm E = 0.99–2.94 J/mol.K. Practical significance: reducing the number of time-consuming and expensive installation experiments during the processing of Hg–Se compositions to optimize the temperature and pressure values of the vacuum treatment process distillation in order to obtain Se-containing products of a given composition.

Realizing Enhanced Thermoelectric Performance and Hardness in Icosahedral Cu5 FeS4-x Sex with High-Density Twin Boundaries.

Bornite (Cu5 FeS4 ) is an Earth-abundant, nontoxic thermoelectric material. Herein, twin engineering and Se alloying are combined in order to further improve its thermoelectric performance. Cu5 FeS4-x Sex (0 ≤ x≤ 0.4) icosahedral nanoparticles, containing high-density twin boundaries, have been synthesized by a colloidal method. Spark plasma sintering retains twin boundaries in the pellets sintered from Cu5 FeS4-x Sex colloidal powders. Thermoelectric property measurement demonstrates that alloying Se increases the carrier concentration, leading to much-improved power factor in Se-substituted Cu5 FeS4 , for example, 0.84 mW m-1 K-2 at 726 K for Cu5 FeS3.6 Se0.4 ; low lattice thermal conductivity is also achieved, due to intrinsic structural complexity, distorted crystal structure, and existing twin boundaries and point defects. As a result, a maximum zT of 0.75 is attained for Cu5 FeS3.6 Se0.4 at 726 K, which is about 23% higher than that of Cu5 FeS4 and compares favorably to that of reported Cu5 FeS4 -based materials. In addition, the Cu5 FeS4-x Sex samples containing twin boundaries also obtain improved hardness compared to the ones fabricated by melting-annealing or ball milling. This work demonstrates an effective twin engineering-composition tuning strategy toward enhanced thermoelectric and mechanical properties of Cu5 FeS4 -based materials.

Enhancing thermoelectric performance of SrFBiS2−xSexvia band engineering and structural texturing

SrFBiS2 is a quaternary n-type semiconductor with rock-salt-type BiS2 and fluorite-type SrF layers alternately stacked along the c axis. The tunability of the crystal and electronic structures as well as the intrinsically low thermal conductivity make this compound a promising parent material for thermoelectric applications. In the current work, we show that alloying of Se and S in SrFBiS2 reduces the optical band gap with the second conduction band serving as an electron-transport medium, simultaneously increasing the electron concentration and effective mass. In addition, the raw material Bi2Se3 is shown to act as liquid adjuvant during the annealing process, favoring preferred-orientation grain growth and forming strengthen microstructural texturing in bulk samples after hot-pressed sintering. Highly ordered lamellar grains are stacked perpendicular to the pressure direction, leading to enhanced mobility along this direction. The synthetic effect results in a maximum power factor of 5.58 μW cm−1 K−2 at 523 K for SrFBiSSe and a peak zT = 0.34 at 773 K, enhancements of 180% compared with those of pristine SrFBiS2.

Expand band gap and suppress bipolar excitation to optimize thermoelectric performance of Bi0.35Sb1.65Te3 sintered materials

Bismuth-telluride-based alloys have been the state-of-art thermoelectric candidates near room temperature. However, sintered samples with higher ZT values in a wide temperature range are still urgently needed for further applications. Especially owing to the small band gap, the minority carriers are boosted at higher temperature and the thermoelectric properties are severely deteriorated. Here, we prepared p-type Bi0.35Sb1.65Te3-xSex samples by hot pressing to enlarge the band gap and suppress the bipolar excitation. Although the carrier concentrations are slightly increased by the tiny Se alloying, the Seebeck coefficients above 400 K are significantly improved, and the bipolar and lattice contributions to thermal transport are obviously reduced. The x = 0.04 sample thus achieves an average value of 1.1 between 300 and 500 K, and the constructed thermoelectric device produces an output power density of 0.36 W cm−2 and conversion efficiency of 5.24% at a temperature difference of 200 K. These results suggest that Se-doped Bi0.35Sb1.65Te3 is a robust candidate for low-grade heat harvest near room temperature.

Hydrogen states in mixed-cation CuIn(1-x)GaxSe2 chalcopyrite alloys: a combined study by first-principles density-functional calculations and muon-spin spectroscopy

ABSTRACT First-principles calculations were performed jointly with muon-spin (μSR) spectroscopy experiments in order to examine the electrical activity of hydrogen in mixed-cation chalcopyrite Cu(In,Ga)Se (CIGS) alloys and other related compounds commonly used as absorbers in solar-cell technology. The study targeted the range of Ga concentrations most relevant in typical solar cells. By means of a hybrid-functional approach the charge-transition levels of hydrogen were determined and the evolution of the defect pinning level, E(+/–), was monitored as a function of the Ga content. The use of E(+/–) as a metric of the charge-neutrality level allowed the alignment of band structures, thus providing the band offsets between the CuInSe compound and the CIGS alloys. The μSR measurements in both thin-film and bulk CIGS materials confirmed that the positively charged state is the thermodynamically stable configuration of hydrogen for p-type conditions. The interpretation of the μSR data further addressed the existence of a metastable quasi-atomic neutral configuration that was resolved from the calculations and led to a formation model for muon implantation.

Superconductivity in efficient thermoelectric material Cu3Sb0.98Al0.02Se4

Inspired by the rich physical properties of thermoelectric materials, we have investigated the electrical transport, vibrational, and structural properties of efficient thermoelectric material Cu3Sb0.98Al0.02Se4 under pressure up to 40.1 GPa. At a critical pressure of 8.5 GPa, a superconducting phase sets in and persists in the pressure range studied. A superconducting dome in the temperature-pressure phase diagram of Cu3Sb0.98Al0.02Se4 was observed. Meanwhile, pressure-induced structural transition from its initial phase to disorder body-centered cubic structure in Cu3Sb0.98Al0.02Se4 has been verified by the X-ray diffraction and Raman scattering measurements. Interestingly, the onset of superconductivity coincides with the structural transition, accompanied with the reduction of volume. The superconducting phase was observed in the ultimate formation of the Cu–Sb–Al–Se alloy and was determined to be Im-3m. Based on Hall coefficient measurements, we evaluated the carrier concentration of Cu3Sb0.98Al0.02Se4, which shows a dramatic increase in the superconducting state. These results suggest that the novel superconductor is realized through the charge transfers and the first-order structural transformation.

Control of Cu-doping behavior in n-type Cu0.01Bi1.99Te2.7Se0.3 polycrystalline bulk via fabrication technique change

Bi–Te-based alloys are potential candidates for use in thermoelectric (TE) modules for low-mid-temperature energy harvesting. However, n -type Bi–Te–Se alloys are inferior to their p -type counterparts in terms of TE performance. It has been found that doping Cu atoms into n -type Bi–Te–Se alloys is effective in improving the TE properties; however, different studies have reported contrasting roles of Cu dopants in the transport properties of Bi–Te–Se alloys. This is attributed to the complex doping behaviors of Cu atoms. In this study, it is demonstrated that employing an appropriate fabrication technique can enable more Cu dopants to be directed to specific atomic sites than others. As part of the study, two n -type polycrystalline Cu 0.01 Bi 1.99 Te 2.7 Se 0.3 bulk samples are respectively fabricated via melt-spinning followed by spark plasma sintering, and via ball-milling followed by spark plasma sintering. The majority of Cu dopants in the melt-spun sample are suspected to exist in between Te 1 –Te 1 atomic layers (van der Waals gap), given the elongated c -axis, increased Hall carrier concentration, and improved non-degenerate mobility (intercalated Cu generates one electron and acts as an electric connector). Resultantly, a ~30% enhancement in the TE figure-of-merit (~0.92 at 360–400 K) is achieved in the melt-spun sample, relative to the ball-milled sample, wherein Cu atoms substitute Bi atoms.

Experimental and Theoretical Studies of the Electronic Band Structure of Bulk and Atomically Thin Mo1-x W x Se2 Alloys.

We present studies focused on the evolution of the electronic band structure of the Mo1–xWxSe2 alloy with the tungsten content, which was conducted by combining experimental and theoretical methods. Employed spectroscopic techniques, namely, photoreflectance, photoacoustic spectroscopy, and photoluminescence, allowed observing indirect and direct transitions at high and beyond high-symmetry points of the Brillouin zone (BZ). Two excitons (A and B) associated with the K point of the BZ were observed together with other optical transitions (C and D) related to band nesting. Moreover, we have also identified the indirect transition for the studied crystals. Obtained energies for all transitions were tracked with a tungsten content and compared with results of calculations performed within density functional theory. Furthermore, based on the mentioned comparison, optical transitions were assigned to specific regions of the BZ. Finally, we have obtained bowing parameters for experimentally observed features, for, i.e., thin-film samples: b(A) = 0.13 ± 0.03 eV, b(B) = 0.14 ± 0.03 eV, b(C) = 0.044 ± 0.008 eV, and b(D) = 0.010 ± 0.003 eV.

Extraction of Selenium and Tellurium from CaCl2–LiCl-Based Molten Chlorides Containing Na2Se, Na2Te, and CaO

This study was conducted considering the separation of long-lived fission products of 79Se from vitrified high-level radioactive wastes. The redox behavior of Se on various electrodes was investigated in CaCl2 melts containing Na2Se and CaO at 1093 K. Se2− ions were anodically oxidized to form selenide compounds on Cu and Ni electrodes, which were not affected by presence of O2− ions. Potentiostatic electrolysis using a Ni anode yielded liquid Ni–Se alloy and Ni was thus evaluated as a suitable anode material for extracting Se. A chemical reaction using NiO and Ni metal was investigated for the extraction of Se as an alternative to electrodeposition. In addition, anodic deposition behaviors of Te and Se on Ni in an equimolar CaCl2–LiCl melt containing Na2Se, Na2Te, CaO, BaCl2, SrCl2, CsCl, KCl, and EuCl2 were investigated. The potential difference between the Ni telluride and selenide formations was about 0.20 V, indicating that Te can be extracted prior to Se. The NiO/Ni apparatus consisting of a Ni rod immersed in NiO powder placed in a MgO crucible was used to extract Te and Se in two steps. Most of Te was first extracted. Then, the remaining Te and Se were almost completely extracted.

Observation of Strong Valley Magnetic Response in Monolayer Transition Metal Dichalcogenide Alloys of Mo0.5W0.5Se2 and Mo0.5W0.5Se2/WS2 Heterostructures.

Monolayer transition metal dichalcogenide (TMD) alloys have emerged as a unique material system for promising applications in electronics, optoelectronics, and spintronics due to their tunable electronic structures, effective masses of carriers, and valley polarization with various alloy compositions. Although spin-orbit engineering has been extensively studied in monolayer TMD alloys, the valley Zeeman effect in these alloys still remains largely unexplored. Here we demonstrate the enhanced valley magnetic response in Mo0.5W0.5Se2 alloy monolayers and Mo0.5W0.5Se2/WS2 heterostructures probed by magneto-photoluminescence spectroscopy. The large g factors of negatively charged excitons (trions) of Mo0.5W0.5Se2 have been extracted for both pure Mo0.5W0.5Se2 monolayers and Mo0.5W0.5Se2/WS2 heterostructures, which are attributed to the significant impact of doping-induced strong many-body Coulomb interactions on trion emissions under an out-of-plane magnetic field. Moreover, compared with the monolayer Mo0.5W0.5Se2, the slightly reduced valley Zeeman splitting in Mo0.5W0.5Se2/WS2 is a consequence of the weakened exchange interaction arising from p-doping in Mo0.5W0.5Se2 via interlayer charge transfer between Mo0.5W0.5Se2 and WS2. Such interlayer charge transfer further evidences the formation of type-II band alignment, in agreement with the density functional theory calculations. Our findings give insights into the spin-valley and interlayer coupling effects in monolayer TMD alloys and their heterostructures, which are essential to develop valleytronic applications based on the emerging family of TMD alloys.

MATHEMATICAL MODELING AND OPTIMIZATION OF THE LECTRODEPOSITION PROCESS OF ANTIMONY-SELENIUM SYSTEM

Antimony selenide (Sb2Se3), is an excellent photovoltaic absorber due to its high absorption coefficient (> 105 cm–1) at the visible region and 1.17 eV band gap. In recent years, the power conversion efficiency of Sb2Se3 thin film solar cells has gradually enhanced. Therefore, given the great interest in this material, this work is devoted to the study of a mathematical model for the optimization of the preparation of thin Sb–Se films by the electrochemical method. The study was conducted by potentiodynamic, potentiostatic and galvanostatic methods carried out under different conditions at Pt, Cu and Ni elec-trodes. The kinetics and mechanism of the electroreduction of antimony and selenite ions in the tartaric acid were studied separately for the electrochemical deposition. On the basis of cyclic polarization, X-ray phase and SEM-EDX analyses, it is found that Sb–Se thin films are deposited on Pt and Ni electrodes, but not on Cu electrode. The mathematical calculations were performed in the OptimME software package using specially developed software for this process. By studying the effects of various factors (concentration of the initial components, temperature, current density, etc.), the optimal electrolysis mode and electrolyte composition for the co-deposition process were selected. Based on these results, Student and Fisher criteria were assigned for future purposes and regression coefficients were estimated. The obtained regression equation determines the electrolyte content and the electrolysis conditions, which allows precipitating the Sb–Se alloy containing the required amount of Sb. Calculations and experimental results show that the error of the regression equation for obtaining the Sb–Se alloy is =6.4%.

Role of grain alignment and oxide impurity in thermoelectric properties of textured n-type Bi–Te–Se alloy

A nanostructured n-type Bi2Te2.7Se0.3 (BTS) alloy with a unique microstructure was prepared using a facile melting-rotation-quenching process followed by ball-milling and uniaxial hot-press sintering at 623 K. Anisotropy in the resulting microstructure showed anisotropic electrical and thermal transport properties in two directions normal to the pressing axis. The texture of the nanostructured BTS alloy was analyzed by x-ray diffraction and scanning electron microscopy. Based on the geometric phase analysis of a high resolution transmission electron microscopy images, abundant dislocations, high grain boundary density, and oxide impurity were identified, which act as phonon scattering centers. Higher anisotropy in thermal conductivity combined with oxide impurity resulted in an ultra-low phonon thermal conductivity of ∼0.305 W mK−1 at 423 K in the nanostructured n-type BTS in the direction parallel to the pressing axis. Laser power- and temperature-dependent Raman spectra analyses provided a deeper insight into the anisotropy in thermal transport properties. Optimum power factor and low thermal conductivity, due to the combination of grain alignment and oxide impurity, resulted in a dimensionless figure of merit (zT ) value of ∼0.75 at 423 K. In comparison, the high and opposite temperature dependences of electrical conductivity and thermal conductivity led to a better average zT value of ∼0.68 and a thermoelectric energy conversion efficiency percentage of ∼4.4% in the operating temperature range (300–423 K) in the direction parallel to the pressing axis.

Radiative Recombination at Ion-Induced Defects in Cu(In,Ga)Se2 Alloy Thin Films

Radiative Recombination at Ion-Induced Defects in Cu(In,Ga)Se2 Alloy Thin Films

Carbon Fibers Coated with Ternary Ni–Co–Se Alloy Particles as a Low-Cost Counter Electrode for Flexible Dye Sensitized Solar Cells

Compared to flat devices based on rigid substrates, cable-shaped dye-sensitized solar cells hold advantages of smaller size, light weight, facile fabrication, flexibility, and low cost, thus a prom...

Atomic layer deposition of chalcogenides for next-generation phase change memory

Atomic layer deposition (ALD) of chalcogenides is an essential technique for low-power and high-capacity phase-change memory. This review provides an overview on the recent progress in the ALD of chalcogenides including Ge–Sb–Te and Ge–Se alloys.

Growth and Characterization of CuInGaSe2 Single Crystal

The chalcopyrite Cu(In,Ga)Se2 (CIGS) alloy system has received strong interest in recent years because of its potential for the development of high efficiency and low cost solar cells. The bandgap energy can be varied between 0.9 and 1.68 eV by composition ratio of In and Ga and the absorption coefficient is very high of abobe 105 cm-1. In our previous work1, I-III-VI2 chalcopyrite compound Cu(In0.2, Ga0.8)Se2 (CIGS) single crystal was successfully grown by traveling heater method (THM). The powder X-ray diffraction (XRD) pattern showed preferred orientations of (112), (220) and (312) planes, confirming the chalcopyrite structure. In Raman spectra, the A1 mode peaks expected for CIGS were observed, and no secondary phases were observed. The full-width at half-maximum (FWHM) of the X-ray rocking curve (XRC) for the (112) oriented CIGS single crystal is 103 arcsec. The good-quality single-phase CIGS single crystal can be obtained1). In this work, Ga-rich composition ratio CIGS single crystals could be also successfully grown by THM. At the ratio of Ga / (Ga + In) > 0.3, the CIGS changed from n-type conduction to p-type conduction. It was assumed that Se vacancies are reduced with increasing Ga ratio from the results of Energy dispersive X-ray spectroscopy. 1)Nagaoka, et al., Renewable Energy 2015, 79, 127-130.

Roles of bandgrading, lifetime, band alignment, and carrier concentration in high-efficiency CdSeTe solar cells

CdSeTe alloying has significantly increased the efficiency of CdTe-based solar technology. Here, computational modeling compares how different CdSeTe bandgrading, carrier lifetimes, band alignment, and carrier concentrations contribute to transport, recombination, and performance. We find that the gain in photocurrent caused by bandgap narrowing alone is insufficient to describe experimental efficiency gains. Performance can be increased by adjusting CdSeTe compositions and bandgrading depths. However, these performance gains are small relative to the contributions of enhanced lifetime by Se alloying, which can explain record cell efficiency gains with minimal open-circuit voltage loss despite significant bandgap narrowing. Similarly, CdSeTe band alignment shifts can significantly increase performance if front interface recombination is prevalent. For a wide range of CdSeTe grading profiles, the hole density is a critical component to achieve efficiencies exceeding 25%.

Growth and Characterization of Arsenic-Doped CdTe1−xSex Single Crystals Grown by the Cd-Solvent Traveling Heater Method

The photovoltaic performance of CdTe solar cells is mainly limited by low doping and short minority carrier lifetime. Group-V element doping and Se-alloying have a significant impact on tuning these fundamental CdTe properties. In this paper, we report the growth of p-type As-doped, Cd-rich CdTe1−xSex single crystals using metallic Cd as the solvent in the traveling-heater method. The structural and electrical properties of CdTe1−xSex are examined for different Se concentrations. CdTe1−xSex single crystals (0 ≤ x ≤ 0.5) with zincblende structure indicate homogeneous composition. The 1017 cm−3 As-doping activation efficiency can be maintained at close to 50% for x ≤ 0.2. Se alloying leads to bulk minority carrier lifetime exceeding 30 ns for samples doped near 1017 cm−3. These results help us to overcome the current roadblocks in device performance.

Quantum dot phosphors free from hazardous elements: Current status and prospects for established materials and new ZnTe‐based alloys

AbstractTelevision broadcasts are moving to a digital video format based on ultra‐high‐definition (UHD). In addition to high resolution, such UHD displays require a wide color gamut. Quantum dots (QDs) have narrow and color‐tunable emission making these unique light sources for achieving a wide color gamut. Most progress in QDs has been made based on cadmium‐containing materials, as represented by CdSe. These systems have excellent performance in terms of their narrow‐band emission and high emission quantum yield; however, the toxicity of cadmium represents a barrier to practical applications of QD displays. Over the last decade, considerable efforts have been made to develop QDs that do not contain cadmium. Some established alternative materials include InP, CuInS2, and lead halide perovskites. In addition, ZnTe‐based alloy QDs have recently been proposed as promising green and red phosphors. Narrow‐band and green emission (30 nm of full‐width at half‐maximum at a wavelength of 535 nm) has also been reported for Zn (Te, Se) alloy QDs. In this review article, we give a brief overview of progress in established cadmium‐free QDs and describe the current status and future challenges of new cadmium‐free QDs, ZnTe‐based alloy QDs.

Analyzing and Tuning the Chalcogen-Amine-Thiol Complexes for Tailoring of Chalcogenide Syntheses.

The amine-thiol solvent system has been used extensively to synthesize metal chalcogenide thin films and nanoparticles because of its ability to dissolve various metal and chalcogen precursors. While previous studies of this solvent system have focused on understanding the dissolution of metal precursors, here we provide an in-depth investigation of the dissolution of chalcogens, specifically Se and Te. Analytical techniques, including Raman, X-ray absorption, and NMR spectroscopy and high-resolution tandem mass spectrometry, were used to identify pathways for Se and Te dissolution in butylamine-ethanethiol and ethylenediamine-ethanethiol solutions. Se in monoamine-monothiol solutions was found to form ionic polyselenides free of thiol ligands, while in diamine-monothiol solutions, thiol coordination with polyselenides was predominately observed. When the relative concentration of thiol is increased to that of Se, the chain length of polyselenide species was observed to shorten. Analysis of Te dissolution in diamine-thiol solutions also suggested the formation of relatively unstable thiol-coordinated Te ions. This instability of Te ions was found to be reduced by codissolving Te with Se in diamine-thiol solutions. Analysis of the codissolved solutions revealed the presence of atomic interaction between Se and Te through the identification of Se-Te bonds. This new understanding then provided a new route to dissolve otherwise insoluble Te in butylamine-ethanethiol solutions by taking advantage of the Se2- nucleophile. Finally, the knowledge gained for chalcogen dissolutions in this solvent system allowed for controlled alloying of Se and Te in PbSenTe1-n material and also provided a general knob to alter various metal chalcogenide material syntheses.