FP-LAPW calculations of structural, electronic, and optical properties of alkali metal tellurides: M2Te [M: Li, Na, K and Rb]

Structural, electronic, and optical properties of alkali metal tellurides M₂Te [M: Li, Na, K, and Rb] are investigated in the framework of density functional theory within generalized gradient approximation. The calculated structural parameters are in excellent agreement with the experimental data. The electronic band structure calculations show that tellurides of Li, K, and Rb have an indirect fundamental energy band gap, whereas Na₂Te has a direct fundamental energy band gap. To explicate the contribution of anion and cation states to the electronic band structure, the electronic density of states for these compounds has been analyzed. Optical properties such as complex dielectric function, absorption coefficient, refractive index, extinction coefficient, and reflectivity are reported for a wide range of photon energy and are discussed on the basis of corresponding electronic band structure. Furthermore, the electron energy-loss functions for M₂Te compounds are also predicted. In order to validate the performance of the ab initio calculation reported herein, we systematically study the electronic and optical properties of wide band gap M₂Te compounds and compare them with available theoretical and experimental data of M₂O, M₂S, and M₂Se compounds.     

Emerging two-dimensional tellurides

Two-dimensional (2D) materials are at the forefront of current materials research due to their exciting and unique properties. 2D tellurides are emerging materials which are yet to be fully explored. To provide an overview of this emergent field, in this review, we discuss the structure, properties, synthesis methods, and applications of selected 2D tellurides, with stoichiometry of M_xTe_y, and M_xN_yTe_z, (M, N are metal atoms). We present a summary of the latest advances in modeling, experimental synthesis, and characterization of 2D tellurides. Additionally, stress and strain-induced tunability of the physical properties have been reviewed, with a focus on the application of 2D tellurides in electronic, optoelectronic, and magnetic devices. We have discussed many emergent quantum properties of these materials. Finally, we conclude with a perspective on the future of 2D metal tellurides.     

New Class of Electrocatalysts Based on 2D Transition Metal Dichalcogenides in Ionic Liquid

The optimization of traditional electrocatalysts has reached a point where progress is impeded by fundamental physical factors including inherent scaling relations among thermokinetic characteristics of different elementary reaction steps, non‐Nernstian behavior, and electronic structure of the catalyst. This indicates that the currently utilized classes of electrocatalysts may not be adequate for future needs. This study reports on synthesis and characterization of a new class of materials based on 2D transition metal dichalcogenides including sulfides, selenides, and tellurides of group V and VI transition metals that exhibit excellent catalytic performance for both oxygen reduction and evolution reactions in an aprotic medium with Li salts. The reaction rates are much higher for these materials than previously reported catalysts for these reactions. The reasons for the high activity are found to be the metal edges with adiabatic electron transfer capability and a cocatalyst effect involving an ionic‐liquid electrolyte. These new materials are expected to have high activity for other core electrocatalytic reactions and open the way for advances in energy storage and catalysis.     

Clusters stuffed inside frameworks: Electronic structure theory

Summary A zeolite, or other framework material, can be used as a template to form regular 3D arrays of nanosize clusters stuffed inside the framework cages. The aluminosilicate zeolite framework materials have wide electronic bandgaps, so that the stuffed species can produce new active electronic states within that bandgap. We discuss several real and model examples of such systems. We start with a framework of pure silicon, which is the silicon clathrate, and discuss its properties when stuffed with a single alkali atom in each cage. Caged structures of clathrates are similar to those of zeolites and can house alkali metal atoms in a periodic fashion with spacing varying from 5 to 15 Å Next we investigate a model system of semiconductor clusters (Si) in the SiO₂ framework in the sodalite geometry. Sodalite contains \-cages which are building blocks common to the structure of many important zeolites. We investigate theoretically atomic geometries, energetics and electronic properties of small semiconductor clusters in silica-sodalite. We also consider metal atom Na clusters in naturally occurring sodalite. We find that introducing Si semiconductor clusters within the cages of zeolites gives rise to flat electronic bands in the bandgap of the host, while alkali metal clusters give broad bands. The electronic properties are found in many cases to be dominated by many-body electronic correlation effects.     

A general in situ hydrothermal rolling-up formation of one-dimensional, single-crystalline lead telluride nanostructures

In this study we demonstrate that one-dimensional (1D) nanostructured lead telluride (PbTe) can be synthesized in a hydrothermal reaction between lead foil and tellurium powder. The resulting materials were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The formation of the 1D structure can be explained by an in situ hydrothermal rolling-up mechanism whereby PbTe is formed hydrothermally and deposited on the lead substrate. The lead underneath the PbTe layer is then selectively etched by a cetyltrimethylammonium bromide solution, thus allowing the PbTe to roll up into 1D structures. This method can be extended to prepare other 1D tellurides, including CdTe, Cu(2)Te, and Ag(2)Te.     

Quasi‐Monolayer Black Phosphorus with High Mobility and Air Stability

Black phosphorus (BP) exhibits thickness‐dependent band gap and high electronic mobility. The chemical intercalation of BP with alkali metal has attracted attention recently due to the generation of universal superconductivity regardless of the type of alkali metals. However, both ultrathin BP, as well as alkali metal‐intercalated BP, are highly unstable and corrode rapidly under ambient conditions. This study demonstrates that alkali metal hydride intercalation decouples monolayer to few layers BP from the bulk BP, allowing an optical gap of ≈1.7 eV and an electronic gap of 1.98 eV to be measured by photoluminescence and electron energy loss spectroscopy at the intercalated regions. Raman and transport measurements confirm that chemically intercalated BP exhibits enhanced stability, while maintaining a high hole mobility of up to ≈800 cm² V^?1 s^?1 and on/off ratio exceeding 10³. The use of alkali metal hydrides as intercalants should be applicable to a wide range of layered 2D materials and pave the way for generating highly stable, quasi‐monolayer 2D materials.     

Computer Simulation of Liquid Copper Tellurides and Silver Selenide from Diffraction Data

The structural models of liquid Ag₂Se, CuTe, and Cu₂Te are constructed from available diffraction data using molecular dynamics simulations with the BELION algorithm. The structural characteristics of the models are in good agreement with the diffraction data, and the calculated atomization energies agree with thermodynamic estimates. The charge state of the Ag ion is close to 1+, and those of the Cu ions in both tellurides are close to 0.3+. The structures of the three chalcogenides, particularly that of Cu₂Te, are rather loose. The simulation results on the distribution of Voronoi polyhedra and pore size attest to significant local structural inhomogeneity, particularly pronounced in Cu₂Te. The self-diffusion coefficients of the constituent components in the melts are evaluated.     

Structural, Electronic Properties and Fermi Surface of ThCr2Si2-Type Tetragonal KFe2S2, KFe2Se2, and KFe2Te2 Phases as Parent Systems of New Ternary Iron-Chalcogenide Superconductors

The first principles FLAPW–GGA method was used for the comparative study of the structural and electronic properties of three related tetragonal ThCr₂Si₂-type phases KFe₂ Ch ₂, where Ch are S, Se, and Te. The main trends in electronic bands, densities of states, and Fermi surfaces for AFe₂ Ch ₂ were analyzed in relation to their structural parameters. We found that anion replacements (S↔Se↔Te) produce no critical changes in the electronic structure of KFe₂ Ch ₂ phases. On the other hand, our analysis of structural and electronic parameters for hypothetical KFe₂Te₂ allows us to propose this system as a perspective parent phase for search of new iron-chalcogenide superconducting materials.     

Metallotropic liquid crystals formed by surfactant templating of molten metal halides

Liquid crystals consist of anisotropic molecular units, and most are organic molecules. Materials incorporating metals into anisotropic molecules, described as metallomesogens, have been prepared. Anisotropic structures such as one-dimensional chains and two-dimensional layers are frequently observed in solid-state inorganic materials, however, little is understood about structural organization in melts of such materials. Achieving liquid-crystalline behaviour in inorganic fluids should be possible if the anisotropic structure can be retained or designed into the molten phase. We demonstrated the ability to engineer zeolite-type structures into metal halide glasses and liquids. In this work we have engineered lamellar, cubic and hexagonal liquid-crystalline structure in metal-halide melts by controlling the volume fraction and nature of the inorganic block (up to 80 mol%) with respect to alkylammonium surfactants. The high metal content of these liquid-crystalline systems significantly advances the field of metallomesogens, which seeks to combine magnetic, electronic, optical, redox and catalytic properties common to inorganic materials with the fluid properties of liquid crystals.     

Stabilizing Atomically Dispersed Catalytic Sites on Tellurium Nanosheets with Strong Metal–Support Interaction Boosts Photocatalysis

The utilization of appropriate supports for constructing single‐atom‐catalysts is of vital importance to achieve high catalytic performances, as the strong mutual interactions between the atomically dispersed metal atoms and supports significantly influence their electronic properties. Herein, it is reported that atomic cobalt species (ACS) anchored 2D tellurium nanosheets (Te NS) can act as a highly active single‐atom cocatalyst for boosting photocatalytic H₂ production and CO₂ reduction reactions under visible light irradiation, wherein Te NS serves as the ideal support material to bridge the light absorbers and ACS catalytic sites for efficient electron transfer. X‐ray absorption near‐edge structure spectroscopy reveals that the ACS are built by a Co center coordinated with five Co? O bonding, which are anchored on Te NS through one Co? Te bonding. The strong mutual interaction between the Te NS and ACS alters the electronic structure of Te NS, inducing the introduction of intermediate energy states, which act as trap sites to accommodate the photogenerated electrons for promoting photocatalytic reactions. This work may inspire further capability in designing other Te‐based single‐atom‐catalysts for highly efficient solar energy conversion.     

Re Doping in 2D Transition Metal Dichalcogenides as a New Route to Tailor Structural Phases and Induced Magnetism

Alloying in 2D results in the development of new, diverse, and versatile systems with prospects in bandgap engineering, catalysis, and energy storage. Tailoring structural phase transitions using alloying is a novel idea with implications in designing all 2D device architecture as the structural phases in 2D materials such as transition metal dichalcogenides are correlated with electronic phases. Here, this study develops a new growth strategy employing chemical vapor deposition to grow monolayer 2D alloys of Re‐doped MoSe₂ with show composition tunable structural phase variations. The compositions where the phase transition is observed agree well with the theoretical predictions for these 2D systems. It is also shown that in addition to the predicted new electronic phases, these systems also provide opportunities to study novel phenomena such as magnetism which broadens the range of their applications.     

金属点阵材料的研究进展

金属点阵材料是一种具有高孔隙率以及周期性结构的先进轻质多功能材料。重点评述了金属点阵材料的分类、金属三维点阵材料的主要制备方法以及点阵结构制备过程中的连接技术,并归纳了目前对其力学性能表征的一些成果,最后从结构与功能两方面介绍了金属点阵材料特有的优良性能以及应用,并展望了其未来的研究趋势。     

Structure and topological transport in Pb-doping topological crystalline insulator SnTe(001) film

Topological crystalline insulator(TCI) as a new type of topological materials has attracted extensive research interests for its tunable topological properties. Due its symmetry topological protection essence,the structure investigation provides a solid basement for tuning its topological transport properties.On Sr TiO_3(111) substrate, the Sn Te film was found to be epitaxial growth only along [001] while not[111] direction. The detailed structural study was performed and a structural model was proposed to elucidate epitaxial growth of the Sn Te(001) film. The transport properties of Sn Te(001) film were further investigated and a typical weak anti-localization effect was observed. By Pb-doping into Sn Te, the bulk carriers were inhibited and its topological surface states were strengthened to induce the enhanced surface transport contribution. With tunable multiple transport channels from the even Dirac cones, the TCI Sn Te film systems will have the potential application in future spintronics devices.     

磁性金属有机复合材料的合成与应用

金属有机框架材料(MOFs)是一种将金属离子中心与有机配体通过配位键结合起来的一类具有网格结构的材料。由于金属离子以及有机配体的多样性,MOFs的结构也具有多样性。磁性金属有机复合材料是一种新型的复合材料,既结合了MOFs的网状结构及结构多变性的优点,又结合了磁性材料易于分离且可重复利用的特性,使得这种材料在药物载体、多相催化、选择吸附等多种方面都有着较为广泛的应用。以经典的几类MOFs为分类依据,研究了它们与磁性材料结合形成新型复合材料的方法,同时概括了这些新型复合材料在不同领域的应用,最后提出了该材料目前所存在的问题,并对今后的研究方向进行了展望。     

Zr(IV) basic carbonate complexes as precursors for new materials: synthesis of the zirconium-surfactant mesophase

Soluble anionic carbonate complexes of Zr(IV) are produced by addition of Zr(IV) salts to the excess of an alkali metal or ammonium carbonate. The solutions are metastable at pH 7-10 and can be used as the precursors for the synthesis of new materials, as illustrated by the example of the surfactant containing mesophase with a wormhole-like structure, prepared by means of reaction with cetyltrimethylammonium bromide.     

新型液态金属电池正极材料的探索研究

利用液态金属电池储能是近年来发展起来的一种新型电化学储能技术,具有成本低、寿命长等优点,在大型储能领域具有广阔的应用前景。传统单一组分的正极材料面临熔点高、电压低等问题,而合金材料则给液态金属电池正极材料提供了新的可能。本文通过分子动力学方法计算多种适用于液态金属电池正极材料的金属和合金材料(Bi、Sb、Te、Sn、Pb),经过多尺度计算模拟,首先找到了30种二元合金和三元合金,分析这些合金材料的形成能,发现均为负值,理论上说明这30种二元合金和三元合金均可以稳定存在。而后,筛选出具有较低熔点(<500℃)的正极合金,分别是SnSb、HgTl、InBi、PbSb、HgIn、InTe、GaSb、AlSb、CdSnSb2、ZnSb。进一步分析合金正极材料的态密度,选出7种离子传输能力较强的正极合金:PbSb、HgIn、CdSnSb2、ZnSnSb2、InTe、SnSb和SnTl4Te3,模拟计算其以锂为负极情况下的开路电压,结果表明,以SnSb为正极材料时,开路电压可达0.65 V。     

Metal Thio‐ and Selenophosphates as Multifunctional van der Waals Layered Materials

Since the discovery of Dirac physics in graphene, research in 2D materials has exploded with the aim of finding new materials and harnessing their unique and tunable electronic and optical properties. The follow‐on work on 2D dielectrics and semiconductors has led to the emergence and development of hexagonal boron nitride, black phosphorus, and transition metal disulfides. However, the spectrum of good insulating materials is still very narrow. Likewise, 2D materials exhibiting correlated phenomena such as superconductivity, magnetism, and ferroelectricity have yet to be developed or discovered. These properties will significantly enrich the spectrum of functional 2D materials, particularly in the case of high phase‐transition temperatures. They will also advance a fascinating fundamental frontier of size and proximity effects on correlated ground states. Here, a broad family of layered metal thio(seleno)phosphate materials that are moderate‐ to wide‐bandgap semiconductors with incipient ionic conductivity and a host of ferroic properties are reviewed. It is argued that this material class has the potential to merge the sought‐after properties of complex oxides with electronic functions of 2D and quasi‐2D electronic materials, as well as to create new avenues for both applied and fundamental materials research in structural and magnetic correlations.     

Inorganic molecular wires: Physical and functional properties of transition metal chalco-halide polymers

The rapid development of nanotechnology has lead to demands on new one-dimensional materials with new functional properties. Carbon nanotubes have received most attention, followed by nanowires of very different kinds. Most recently inorganic molecular wires - particularly molybdenum halide or chalcogenide cluster polymers - have emerged as a new type of one-dimensional materials with remarkable molecular-scale functionality. These transition metal chalco-halide molecular wires are unique in terms of structure and molecular properties, setting them apart from the plethora of nanowires and nanotubes discovered in recent years.Their one-dimensional polymer structure gives rise to some very unusual physical properties. Anionic bridges which bind Mo clusters together into one-dimensional chains are extraordinarily strong, yet highly deformable, giving rise to exceptionally high Young’s moduli and nonlinear mechanical properties respectively. The very weak interaction between individual polymer chains within crystalline bundles leads to observation of extreme one-dimensional electronic and magnetic character on one hand, and also to easy dispersion in common polar solvents and ultralow shear moduli on the other. The sulfur atoms within the structure facilitate diverse functionalization chemistry to thiol-containing molecules, such as proteins. The connectivity of the molecular wire ends to gold nanoparticles and surfaces with covalent bonds and good electronic coupling enable self-assembled molecular-scale connections to be made between individual molecules.Experimental and theoretical progress in the field has been extremely rapid since 2004 and in this review we try and summarize the most important structural, mechanical, electronic and magnetic properties of molybdenum chalco-halide molecular wires. We also discuss their functional properties which make these new materials of great interest for a wide variety of diverse applications including conducting composites, nonlinear optics, field emission, tribology, spin-modulators, molecular and gas sensing and potentially revolutionary applications in molecular electronics.     

Strain-engineering of band gaps in piezoelectric boron nitride nanoribbons

Two-dimensional atomic sheets such as graphene and boron nitride monolayers represent a new class of nanostructured materials for a variety of applications. However, the intrinsic electronic structure of graphene and h-BN atomic sheets limits their direct application in electronic devices. By first-principles density functional theory calculations we demonstrate that band gap of zigzag BN nanoribbons can be significantly tuned under uniaxial tensile strain. The unexpected sensitivity of band gap results from reduced orbital hybridization upon elastic strain. Furthermore, sizable dipole moment and piezoelectric effect are found in these ribbons owing to structural asymmetry and hydrogen passivation. This will offer new opportunities to optimize two-dimensional nanoribbons for applications such as electronic, piezoelectric, photovoltaic, and opto-electronic devices.     

Modelling the role of size, edge structure and terminations on the electronic properties of trigonal graphene nanoflakes

Graphene nanoflakes provide a range of opportunities for engineering graphene for future applications, due to the large number of configurational degrees of freedom associated with the addition of different types of corners and edge states in the structure. Since these materials can, in principle, span the molecular to macroscale dimensions, the electronic properties may also be discrete or continuous, depending on the application in mind. However, since the widespread use of graphene nanoflakes will require them to be predictable, stable and robust against variations associated with some degree of structural polydispersivity, the development of a complete understanding of the relationship between structure, properties and property dispersion is essential. In this paper we used electronic structure computer simulations to model the thermodynamic, mechanical and electronic properties of trigonal graphene nanoflakes with acute (highly reactive) corners. We find that these acute corners introduce new features that are different to the obtuse corners characteristic of hexagonal graphene nanoflakes, as well as different electronic states in the vicinity of the Fermi level. The structure and properties are sensitive to size and functionalization, and may provide new insights into the engineering of graphene nanoflake components.