Se System Research Articles

Electron-phonon driven superconductivity in the novel A15 phase of the Ti–Te system under pressure

We investigate the high-pressure phase diagram of Ti–Te system using first-principles calculations combined with evolutionary crystal structure prediction. Given the isostructural behavior of Se and Te at higher pressures, the same stoichiometric ratios as in the Ti–Se system were found in the Ti–Te system at high pressures. A novel A15 stable phase Ti3Te is predicted under pressure. Following this, its electronic, mechanical, vibrational, dynamical and superconducting properties at 0 GPa have been systematically scrutinized. The Ti-d orbitals occupy mainly at the Fermi level and Ti3Te exhibits intrinsic metallic property. Meanwhile, the electron-phonon coupling constant λ is 1.03, and the calculated superconducting transition temperature Tc (μ∗ = 0.10–0.15) is 14.2-11 K. Furthermore, we have studied the A15 structural candidates that can be formed by Ti and sulphur group elements under pressure. The mechanism of pressure-enhanced superconductivity present in these structures is also elucidated from a microscopic perspective.

The role of chalcogen doping in Fe–N–C catalysts for hydrogen-air polymer electrolyte fuel cells: Selenium doped Fe–N–C

A spectrum of selenium-doped Fe–N–C catalysts is prepared and scrutinized for acidic oxygen reduction reactions to understand the impact of the presence and amount of chalcogen dopants on the catalytic performance as cathode catalyst layers (CCLs) for H2–O2 and H2–air polymer electrolyte membrane fuel cells (PEMFCs). While for a high initial content of Se, all available iron is bonded into iron selenides, a low amount of Se doping yields Fe–N–C catalysts of extensive microporosity, increased nitrogen content, and iron occurring predominantly in the Fe-Nx coordination state. The chemistry of the iron-carbon-selenium (Fe–C–Se) system is studied in detail to elucidate the impact of Se on Fe–N–C catalyst formation during pyrolysis. The performance of the Se-doped platinum group metal-free Fe–N–C catalysts in PEMFCs is compared with their commercially available counterpart. The effect of the catalysts' morphology alternation by ball-milling on their performance is also studied. It is concluded that chalcogen doping (either S or Se doping) indirectly impacts Fe–N–C catalyst activity by controlling carbon scaffold properties, while the idea of a direct impact of chalcogen atoms on the Fe-Nx catalytic centers is challenged.

Screening of Astec® CHIRALDEX™ G-PN and LIPODEX™ D gas chromatography columns for enantioseparation of amphetamine derivatives.

Among different substance classes, New Psychoactive Substances (NPS) comprise chiral amphetamines for stimulant and empathic effects. There is little knowledge in terms of clinical studies about possibly different effects of the two enantiomers of novel amphetamine derivatives. For this reason, there is a big demand for enantioseparation method development of this new substance class. Regarding gas chromatography, cyclodextrins proved to be effective for enantioseparation of NPS. In our attempt, an Astec® Chiraldex™ G-PN column containing 2,6-di-O-pentyl-3-propionyl-γ-cyclodextrin and a Lipodex™ D column containing heptakis-(2,6-di-O-pentyl-O-acetyl)-β-cyclodextrin as chiral selector served as stationary phases in a Shimadzu GCMS-QP2010 SE system. Because of the special coating, maximum temperature is limited to 200 °C isothermal or 220 °C in programmed mode. To ensure detection, trifluoroacetic anhydride (TFAA) was used to increase sample volatility.1 As a result, 35 amphetamines were tested as their TFAA-derivatives. A screening method with a temperature gradient from 140 °C to 200 °C at a heating ramp of 1°C per minute and final time of 5min, showed baseline separation for seven and partial separations for 16 trifluoro acetylated amphetamines using the Chiraldex™ G-PN column. Six baseline and nine partial separations were observed with the Lipodex™ D column, respectively.

Research on the optimization of the clean heating system for regional residential buildings based on the multi-objective optimization strategy

For the residential building district heating (RBDH) system, choosing the appropriate combination of heat sources according to local conditions is the key to improving economic efficiency. In this study, three climatic regions in China were selected, namely, a hot summer and cold winter region, cold region, and severe cold region. Among them, Nanjing, Tianjin, and Shenyang were selected as typical representative cities in the hot summer and cold winter region, cold region, and severe cold region, respectively. Taking the levelized cost of heat (LCOH) as the economic evaluation index and considering the carbon emission cost of the system operation, the energy consumption and the CO2 emissions were analyzed. TRNSYS software was used to simulate and analyze the system performance. The multi-objective optimization based on a genetic algorithm was proposed to optimize system parameters. From an economic point of view, the SA system was suitable for the hot summer and cold winter region, the SAS system was suitable for the cold region, and the SE system was suitable for the severe cold region. The operation control strategy based on quality adjustment can reduce heating energy consumption and maintain indoor temperatures at approximately 20°C. The proportion of clean energy heating in the optimized heating system decreased after the multi-objective optimization strategy. However, the initial investment and maintenance costs of the system were reduced, which reduced the LOCH of the system. Therefore, the multi-objective optimization strategy can effectively reduce the heating costs.

First-principles simulations of magnetic properties of Co- and Ni-doped ZnSe

We purposed to analyze the theoretical ab initio study of ferromagnetism and to estimate Curie temperature of Co2+ and Ni2+ 3d transition metal (TM) ions doped Zn1-x TM x Se compounds for 12.5 % and 6.25 % concentrations of impurity TM(Co, Ni) atoms. The calculations are carried out using the norm-conserving Fritz-Haber-Institute ionic pseudopotentials based on density functional theory within the local spin density approximation and Hubbard U (U(Znd)=4.5 eV; U(Sep)=3.8 eV) corrections. The analysis of the total and partial electron density of states shows the half-metallic ferromagnetic behavior with a half-metallic bandgap. The theoretically obtained total magnetic moments of TM(Co, Ni) doped Zn1-x TM x Se systems are equal to 3 μB and 4 μB, correspondingly.

Selective Activation of Chalcogen Bonding: An Efficient Structuring Tool toward Crystal Engineering Strategies.

ConspectusAmong the noncovalent interactions available in the toolbox of crystal engineering, chalcogen bonding (ChB) has recently entered the growing family of σ-hole interactions, following the strong developments based on the halogen bonding (XB) interaction over the last 30 years. The monovalent character of halogens provides halogen bonding directionality and strength. Combined with the extensive organic chemistry of Br and I derivatives, it has led to many applications of XB, in solution (organo-catalysis, anion recognition and transport), in the solid state (cocrystals, conducting materials, fluorescent materials, topochemical reactions, ...), in soft matter (liquid crystals, gels,···), and in biochemistry. The recognition of the presence of two σ-holes on divalent chalcogens and the ability to activate them, as in XB, with electron-withdrawing groups (EWG) has fueled more recent interest in chalcogen bonding. However, despite being identified for many years, ChB still struggles to make a mark due to (i) the underdeveloped synthetic chemistry of heavier Se and Te; (ii) the limited stability of organic chalcogenides, especially tellurides; and (iii) the poor predictability of ChB associated with the presence of two σ-holes. It therefore invites a great deal of attention of molecular chemists to design and develop selected ChB donors, for the scrutiny of fundamentals of ChB and their successful use in different applications. This Account aims to summarize our own contributions in this direction that extend from fundamental studies focused on addressing the lack of directionality/predictability in ChB to a systematic demonstration of its potential, specifically in crystal engineering, and particularly toward anionic networks on the one hand, topochemical reactions on the other hand.In this Account, we share our recent results aimed at recovering with ChB the same degree of strength and predictability found with XB, by focusing on divalent Se and Te systems with two different substituents, one of them with an EWG, to strongly unbalance both σ-holes. For that purpose, we explored this dissymmetrization concept within three chemical families, selenocyanates R-SeCN, alkynyl derivatives R-C≡C-(Se/Te)Me, and o-carborane derivatives. Such compounds were systematically engaged in cocrystals with either halides or neutral bipyridines as ChB acceptors, revealing their strong potential to chelate halides as well as their ability to organize reactive molecules such as alkenes and butadiynes toward [2+2] cycloadditions and polydiacetylene formation, respectively. This selective activation concept is not limited to ChB but can be effectively used on all other σ-hole interactions (pnictogen bond, tetrel bond, etc.) where one needs to control the directionality of the interaction.

Interface‐Enhanced High‐Temperature Thermoelectricity in Cu1.99Se/B4C Composites with Synergistically Improved Mechanical Strength

AbstractDegenerate semiconductors usually demonstrate a metallic‐like conduction behavior, showing limited carrier mobility at high temperatures. Herein, by incorporating B4C nanoparticles into the Cu1.99Se system, an unusual switch from the “degenerate” to “non‐degenerate” semiconducting behavior is revealed as a result of the engineered interfaces. Heterogeneous interfaces and disordered Cu2Se amorphous phases are introduced in the Cu1.99Se/B4C composites, which generate a trapping effect against the mobile Cu ions, leading to a distinctive “hump” signature for electrical conductivity. Benefiting from this rare high‐temperature thermoelectric response, a high power factor is obtained due to reduced carrier concentration and enhanced mobility, and low lattice thermal conductivity is retained because of relatively stronger anharmonic lattice vibrations. Consequently, the Cu1.99Se + 0.9 vol.% B4C sample at least achieves a maximum thermoelectric figure of merit (ZT) of 2.6 at 1025 K with synergistically enhanced mechanical robustness. The present interface engineering strategy may be applicable to other thermoelectric materials with ionic migration characteristics.

ХАЛЬКОГЕНІДНІ СТЕКЛА: СТРУКТУРНІ І ОПТИЧНІ ВЛАСТИВОСТІ (ОГЛЯД)

Structural properties of chalcogenide glasses mainly on the example of binary As-S(Se) and Ge-S(Se) systems and ternary Ge-As-S(Se) systems, structural models, parameters of short range order of glasses obtained using diffraction methods, EXAFS and Raman spectroscopy are considered. Raman spectra of binary As-S(Se) and Ge-S(Se) systems and ternary Ge-As-S(Se) systems, structural models that are used for interpretation of Raman spectroscopy results are considered. Optical properties of chalcogenide glasses and optical absorption edge in binary and multicomponent systems are discussed. The refractive index and its wavelength dependence, other optical properties are among important parameters that determine the suitability of materials as optical media. Refractive and absorption indexes, optical band gap of chalcogenide glasses can be changed by doping of different elements. The results suggest a combined effect of chemical ordering and topological in such glasses (parameters dependence on average coordination number, composition, nanophase separation, etc.). Importance of study of interrelation of structural and physico- chemical properties is stated. As frequently pointed out by various researchers, chalcogenide glasses are promising materials for various applications because they are transparent over a wide range of wavelengths in the infrared region, they possess high linear and non-linear refractive indices, number of photoinduced effects, low phonon energies and are easy to fabricate. Applications of chalcogenide glasses cover wide range, among them: IR optics, recording and storage of information, xerography, thermoplastic and holographic media, inorganic resists, optical filters, diffraction optical elements, non-linear elements, fiber and integrated optics, etc. Composition-structure-properties correlations are convenient to tailor the physical, optical and other properties of chalcogenide glasses and provide an important reference for the further development of new chalcogenide glasses taking into account their possible applications.

Somatic embryogenesis from mature sorghum seeds: An underutilized genome editing recipient system

Somatic embryogenesis is a process of cell totipotency in vitro, whereby an embryogenic cell develops from vegetative tissues rather than from zygotes after double fertilization. Sorghum is a recalcitrant crop in genetic transformation; previous recipient systems have usually been from immature zygotic embryos, which needed more time and labors to prepare. Here, an efficient 2,4-dichlorophenoxyacetic acid (2,4-D)-induced somatic embryogenesis system from mature sorghum seeds was introduced. 2,4-D can induce two types of calli from a plumular axis section. Low-concentration 2,4-D (e.g., 2 mg/L) induces white and loose non-embryogenic calli (type 1), while high-concentration 2,4-D (e.g., 8 mg/L) induces yellow and compact embryogenic calli (type 2), which can be clearly distinguished by Sudan red staining. Germinating seeds have a long 2-day window for SE induction. Somatic embryogenesis can be enhanced by HDAC inhibitor, trichostatin A (TSA), a histone deacetylase treatment, which shows more SE productivity and a bigger size. Importantly, this easily prepared protocol does not show obvious genotype dependency in sorghum hybrids. In this study, a high-concentration 2,4-D-induced SE system was established from mature sorghum seeds. This finding provides a technical option for the genome editing recipient in sorghum.

NaREP2Se6 (RE = Y, Sm, Gd-Dy): Quaternary Rare-Earth Selenophosphates with Unique 3D {[REP2Se6]-}∞ Framework Built by RESe8 and P2Se6 Motifs and Multiple Properties.

Rare-earth (RE) chalcophosphates have been widely studied because of their abundant structures. Here, five new RE selenophosphates, NaREP2Se6 (RE = Y, Sm, Gd-Dy), were synthesized by a facile RE oxide-boron-selenium solid-state route. They crystallize in the triclinic P1̅ space group, featuring three-dimensional (3D) structures constructed by RESe8 and P2Se6 motifs, different from common 2D RE chalcophosphates A-RE-P2-Q6 (A = alkali metal; Q = S, Se) system. Their structural chemistry and relationship with related phases are analyzed. Both the size of A and the coordination geometry of RE have important influences on the system's structures. Their optical band gaps are tunable from 1.79 to 2.50 eV, and they exhibit diverse magnetic behaviors, including Van-Vleck-type paramagnetism, antiferromagnetism, and ferromagnetism. Their photocurrent responses and thermal stabilities are analyzed as well. Calculation results suggest that the RESe8 and P2Se6 units make a great contribution to the optical properties. This work enriches the chemistry and multifunctional properties of RE chalcophosphates.

THERMODYNAMIC PROPERTIES OF SOME TERNARY COMPOUNDS OF THE ARGYRODITE FAMILY

Compounds of the argyrodite family are valuable environmentally friendly functional materials with mixed ion-electronic conductivity, thermoelectric, photovoltaic, optical, and other properties. This paper presents the results of a thermodynamic study of the Cu8GeS6 and Cu8GeSe6 compounds - representatives of this family using the EMF method with Cu4RbCl3I2 solid electrolyte in the 295-430 K temperature range. From the EMF measurement data, the partial molar functions of copper were calculated in both crystal modifications of the Cu8GeS6 and Cu8GeSe6 compounds, undergoing polymorphic transformations at 330 and 335 K, respectively. Based on solid-phase equilibria diagrams of the Cu-Ge-S(Se) systems, the potential-forming reactions responsible for the partial molar functions of copper in the alloys were determined and the thermodynamic functions of formation and standard entropies of both modifications of these compounds, as well as the thermodynamic functions of their polymorphic transitions, were calculated. The work also presents and analyzes the thermodynamic data for compounds of the argyrodite family available in the literature

Constrained Phosphine Chalcogenide Selenoethers Supported by peri-Substitution

A series of phosphorus and selenium peri-substituted acenaphthene species with the phosphino group oxidized by O, S, and Se has been isolated and fully characterized, including by single-crystal X-ray diffraction. The P(V) and Se(II) systems showed fluxional behavior in solution due to the presence of two major rotamers, as evidenced with solution NMR spectroscopy. Using Variable-Temperature NMR (VT NMR) and supported by DFT (Density Functional Theory) calculations and solid-state NMR, the major rotamers in the solid and in solution were identified. All compounds showed a loss of the through-space JPSe coupling observed in the unoxidized P(III) and Se(II) systems due to the sequestration of the lone pair of the phosphine, which has been previously identified as the major contributor to the coupling pathway.

PHASE EQUILIBRIA IN THE SECTION Cu2Se – Cu3SbSe4

Complex selenides are promising thermoelectric materials in a wide temperature range. Since one of the methods for improving material parameters is the formation of solid solutions, the study of phase equilibria and the determination of the homogeneity regions of the components is relevant. This paper presents the results of a study of the physico-chemical interaction in the CuSe2 – Cu3SbSe4 system. The synthesis of alloys of the CuSe2 – Cu3SbSe4 system (0; 10; 30; 50% 70; 90; 100 mol. % Cu3SbSe4) was carried out by a direct one-temperature method at a maximum synthesis temperature of 1053 K. The obtained alloys were studied by X-ray phase, differential thermal and microstructural analyses. Based on the results of the analyses, it was found that CuSe2 – Cu3SbSe4 system is a partially quasi-binary section of the quasi-ternary Cu2Se–Sb2Se3–Se system. The section of CuSe2 – Cu3SbSe4 is characterized by the passage of four nonvariant processes. The studied section crosses the region of primary crystallization of the phase with congruent melting character - β-Cu2Se and the miscibility gap in liquid phase. The region of boundary solid solutions based on the initial components CuSe2 and Cu3SbSe4 does not exceed 5 mol.%.
 Keywords: selenides; phase diagram; thermal analysis; phase equilibria.

Load characteristics analysis of the water source heat pump heating system using data center waste heat

The number and scale of data centers (DCs) in China are constantly expanding with the advancement of networking and informatization. A large amount of waste heat is dissipated at its end. If this waste heat can be recovered, then achieving carbon neutrality in DCs can be effectively accelerated. At present, water source heat pump (WSHP) are widely used in air-cooled and liquid-cooled DCs of different sizes for waste heat recovery. This study analyzes the equipment type and heating capacity of different brands of WSHP units. Three WSHP heating systems are proposed according to the different locations of waste heat enhancement (SE, TDE, UE). The coupling and matching relationship between user-side heat load demand, DC waste heat load, and energy efficiency of WSHP units under different systems is also investigated. Moreover, the law of energy consumption and energy efficiency changes is analyzed. Thus, this study provides a reference for the DC waste heat recovery system design and equipment development. The results show that the coupling matching relationship between user-side heat load demand, DC waste heat load, and heating COP of WSHP units is Q.N/Q.S=COP′/COP′-1=φ, where φ ranges from 1.1962 to 1.3642. The heating COP of the SE system is the greatest when user-side heat load demand is between 0 and 120 kW. The heating COP of the TDE system is the highest when the user-side heat load demand is between 1750 and 70000 kW. Furthermore, the heating COP of the three WSHP heating system types is related to unit brand when user-side heat load demand is between 120 and 1750 kW.

Glassy and crystalline sodium ternary chalcogenide materials in the Na–As–Se system: Synthesis, properties and relation to crystallization

Sodium chalcogenide compounds, glassy and crystalline, are promising materials for a number of potential applications in non-linear optics (NLO), photovoltaic, and energy conversion and storage. This work deals with the study of the newly synthesized glasses in the Na2Se–As2Se3 chalcogenide system as well as the corresponding ternary crystals, NaAsSe2 and Na3AsSe3. We examine the glass-forming domain in the pseudo-binary system using melt-quenching and mechanical milling techniques. We also analyse the macroscopic and electrical properties of the glasses in comparison with their crystalline counterparts, and the annealed glasses yielding glassy/crystalline alloys.

Non-layered InSe nanocrystalline bulk materials with ultra-low thermal conductivity

Exploring new prototypes for a given chemical composition is of great importance and interest to several disciplines. As a famous semiconducting binary compound, InSe usually exhibits a two-dimensional layered structure with decent physical and mechanical properties. However, it is less noticed that InSe can also adopt a monoclinic structure, denoted as mcl-InSe. The synthesis of such a phase usually requires high-pressure conditions, and the knowledge is quite scarce on its chemical bonding, lattice dynamics, and thermal transport. Here in this work, by developing a facile method combining mechanical alloying and spark plasma sintering, we successfully synthesize mcl-InSe bulks with well-crystallized nanograins. The chemical bonding of mcl-InSe is understood as compared with layered InSe via charge analysis. Low cut-off frequencies of acoustic phonons and several low-lying optical modes are demonstrated. Noticeably, mcl-InSe exhibits a low room-temperature thermal conductivity of 0.6 W·m−1·K−1, which is smaller than that of other materials in the In–Se system and many other selenides. Low-temperature thermal analyses corroborate the role of nanograin boundaries and low-frequency optical phonons in scattering acoustic phonons. This work provides new insights into the non-common prototype of the InSe binary compound with potential applications in thermoelectrics or thermal insulation.

I‐SHARE – INCOSE Systems Heuristics Application Repository: Sharing Systems Engineering Knowhow and Experience

AbstractSystems engineering (SE) is a transdisciplinary discipline that links all the engineering disciplines involved in defining a system throughout its lifecycle. As such, SE involves heuristics to a significant extent. A heuristic relates to a formulation based on experts' experience serving as a guide in the investigation or solution of a problem. To be usable, heuristics should be memorable and pithy. A team of INCOSE Fellows created the INCOSE Systems Heuristics Application Repository, or I‐SHARE in short, in which over 600 SE‐related heuristics are curated and shared, covering subjects that include SE competencies, lifecycle stages, expertise, operational domains, and system attributes. In this paper, we describe the I‐SHARE, the motivation and stages of its creation and compilation, and ways through which this knowledge base can be an invaluable service to the SE community.

Low-temperature anomalies and nanosized levels formation of self-organized structures in the non-crystalline solids of As(Ge)-S(Se) systems

The relationship between low-temperature anomalies of physical and chemical properties and the formation of self-organized structures in non-crystalline solids of the As(Ge)-S(Se) systems is discussed. Obtained temperature dependences for the specific heat capacity and coefficient of linear expansion in the temperature domain , detailing the linear and nonlinear contributions. The influence of the obtaining conditions of non-crystalline solids on the low-temperature behavior of physico-chemical properties and the change in the ratios of various contributions and temperature intervals is considered. The correlation and common features of the formation of self-organized structures of non-crystalline materials in the region of low temperatures and softening temperatures, manifested in the presence of nanolevels of structuring, are analyzed.

Hierarchical Porous Carbon Embedded MoSe2 Effectively Improve Cycle Stability in K‐Se Battery

AbstractIt is a crucial challenge to control the dissolution and diffusion of polyselenides in the K−Se system. Herein, a polar material MoSe2 was introduced into Chitosan‐derived hierarchical porous carbon (MoSe2‐HPC) for the first time by a simple freeze‐dried carbonization method, which was used as host materials of Se. The porous carbon plays a vital role in alleviating volume expansion from Se to K2Se and affording physical restriction effect for generating potassium polyselenides (KPSs). The adsorption experiment can prove that the additive MoSe2 as active site can effectively anchor soluble KPSs by remarkable polar interaction to achieve raising electrochemistry performance. Therefore, the Se@MoSe2‐HPC cathode presents superior cycling stability with a specific capacity of 323.2 mAh g−1 after 500 cycles at 1 C and satisfactory rate performance of 261.7 mAh g−1 at 5 C, demonstrating the great potential of MoSe2 as polar adsorption component for K−Se batteries cathode materials.

Phase diagrams of Bi–Sb–Se–Te system

Bi–Sb–Se–Te is one of the most important material systems for thermoelectric applications. Phase diagrams of its constituent binary and ternary systems are reviewed and assessed. The Bi–Sb–Se–Te isothermal section tetrahedron at 400 °C and liquidus projection tetrahedron were proposed. Ternary compounds are only found in the Bi–Sb–Se system. There are eight three-phase regions at 400 °C and seven primary solidification phases in the Bi–Sb–Se system, including (Bi,Sb), (Bi2)m(Bi2Se3)n, Bi2Se3, Se, Sb2Se3, Bi3Sb5Se2, Bi3Sb12Se15. In the Bi–Sb–Te system, there are four three-phase regions at 400 °C. The (Bi,Sb)2Te3 and (Bi,Sb) are continuous solid solutions. There are six primary solidification phases, including (Bi,Sb)2Te3, (Te), γ, δ, (Bi,Sb), and (Bi2)m(Bi2Te3)n. In the Bi–Se–Te system, there is one three-phase region. (Bi2)m(Bi2Se3)n and (Bi2)m(Bi2Te3)n form a continuous solid solution phase at 400 °C. There are four primary solidification phases, including Bi, (Bi2)m(Bi2(Se,Te)3)n, Bi2(Se,Te)3 and (Se,Te). In the Sb–Se–Te system, there are five three-phase regions and six primary solidification phases, including (Sb), δ-(Sb2Te), γ-(SbTe), Sb2Te3, and (Se,Te). A wide range of (Bi,Sb)2(Se,Te)3 single-phase region was observed in the Bi–Sb–Se–Te quaternary system.