Rajasekharan and Girgis reported that binary systems with intermetallic compounds of a particular crystal structure form a straight line on a map using Miedema parameters. In this paper, the universality of that observation is examined. Observations from a study of 143 binary systems that crystallize in six different crystal structures at AB3 composition are discussed. Prediction of concomitant and mutually exclusive structure types in binary metallic phase diagrams, and of phase transitions among different structure types, has been demonstrated. This behavior is unexpected because Miedema parameters are isotropic in nature and structural energies are generally assumed to be small. We argue in this paper that each point on the map stands for the energy of an unlike atom-pair (A-B) bond, with the bond energy remaining nearly the same at all compositions in the phase diagram. This argument is confirmed by comparing the nearest-neighbour (A-B) bond lengths for the compounds of the structure types CaCu5 and CsCl, when concomitant with MgCu2 structure type. This fact leads to an important conclusion that one can define a bond energy for the metallic unlike-atom-pair bond as is usually done for a conventional chemical bond.
First principles studies were performed in order to find out the possibility of inducing half-metallicity in Heusler Compound CoFeMnSb, by means of alloying it with 3d-transition metal elements. Proper alloying element is selected through the calculations of formation energies. These calculations were tested with different concentrations of alloying elements at different atomic sites. Among the selected transition metal elements Sc and Ti are proposed to be excellent alloying elements particularly at Mn site. By using these alloying elements complete half metallic behaviour is obtained in CoFe…
Minor alloying is widely used to control mechanical properties of metallic glasses (MGs). The present understanding of how a small amount of alloying element changes strength is that the additions lead to more efficient packing of atoms and increased local topological order, which then increases the barrier for shear transformations and the resistance to plastic deformation. Here, we discover that minor alloying can improve the strength of MGs by increasing the chemical bond strength alone and show that this strengthening is distinct from changes in topological order. The results were obtained…
The electronic structure and half-metallic gap of Co$_{2}$MnSi in the presence of crystallographic defects, partial Fe substitution for Mn, and thermal spin fluctuations are studied using the coherent potential approximation and the disordered local moment method. In the presence of 5\% Co or Mn vacancies the Fermi level shifts down to the minority-spin valence-band maximum. In contrast to NiMnSb, both types of Mn antisite defects in Co$_{2}$MnSi are strongly exchange-coupled to the host magnetization, and thermal spin fluctuations do not strongly affect the half-metallic gap. Partial substitu…
Micro- or minor alloying of metallic glasses is of technological interest. An originally ductile Pd-based monolithic bulk metallic glass (Pd$_{40}$Ni$_{40}$P$_{20}$) was selectively manipulated by additions of Fe or Co. The alloying effects were extreme, showing either exceptional ductility upon Co addition or immediate catastrophic failure upon Fe addition when tested under uniaxial compression or 3-point bending. The amorphous structure was characterized prior to deformation with respect to its medium-range order (MRO) using variable resolution fluctuation electron microscopy (VR-FEM). We ob…
The realization of air-stable 2D metals epitaxial to SiC and capped by graphene creates a potentially immense chemical space of 2D metals and alloys that could expand the variety of solid-state excitations unique to 2D metals beyond what is known for graphene and niobium/tantalum chalcogenides. We perform a high-throughput computational survey from first-principles predicting the structures and stabilities of all metals in the periodic table when they intercalate graphene/SiC. Our results not only agrees with all experimentally known metal/SiC structures explored so far, but also reveals consp…
Investigation on Anharmonicity, Vibrational Anisotropy and Thermal Expansion of an Amorphous Ni$_{46}$Ti$_{54}$ Alloy Produced by Mechanical Alloying using Extended X-ray Absorption Fine Structure
提出了一种利用基于累积膨胀的扩展X射线吸收精细结构（EXAFS）分析得到的平行和垂直于原子间键的相关均方相对位移（MSRD）研究非谐性、振动各向异性和热膨胀的方法，并将其应用于机械合金化制备的非晶态Ni $_{46}$ Ti $_{54}$合金。通过在不同温度下对Ni和Ti K边的EXAFS测量，获得了$\text{MSRD}_\parallel$、$\text{MSRD}_\perp$和实分布函数$\varrho_{ij}(r,T)$的累积量$C_1^*$、$C_2^*$和$C_3^*$的热行为，以及与平行和垂直运动有关的爱因斯坦温度和频率，提供了关于原子间势的非谐性的信息。振动各向异性以及垂直运动对总无序和热膨胀的贡献。
In this work we introduce a metal-oxide bond-energy model for alloy oxides based on pure-phase bond energies and bond synergy factors that describe the effect of alloying on the bond energy between cations and oxygen, an important quantity to understand formation and stability of passive films. This model is parameterized for binary cation-alloy oxides using density-functional theory energies and is shown to be directly transferable to multi-component alloy oxides. We parameterized the model for alloy oxide energies with metal cations that form the basis of corrosion resistant alloys, includin…
As a possible alternative to organic-inorganic hybrid perovskite halide, inorganic Cs2SnI6 has drawn more and more research attention recently. In order to find more Cs2SnI6 derivatives as the potential solar cell absorber materials, I- ions in Cs2SnI6 are replaced by other halogen ions and forms the Cs2SnI6-nXn (X=F, Cl, Br; n=1~6) compounds, whose atomic structures, electronic structures and optical absorption are investigated by first principles calculation. When the alloying level n increases, the mean lattice constants, the weighted Sn-X and Cs-X bond lengths all decreases linearly; the b…
Aluminum nitride (AlN) is an important piezoelectric material for a wide range of applications, many efforts are devoted to improving its piezoelectric response by alloying with transition metals (TMs). In this paper, the influence of the type and distribution of TM on the piezoelectric response is discussed for the first time. TM0.0625Al0.9375N with twenty-eight different TMs are investigated, and most show higher values of piezoelectric strain modulus d33 than that of AlN. This is because the TM introduces weaker TM-N bonds and locates closer to the centre of three neighbouring N atoms. The …
An experimental and computational investigation of structure and magnetism in pyrite Co$_{1-x}$Fe$_x$S$_2$: Chemical bonding and half-metallicity
制备了黄铁矿硫属化合物固溶体Co $_{1-x}$ Fe $_x$ S $_2$ 0 <= x <= 0.5的块状样品，用X射线衍射和SQUID磁化强度测量研究了它们的晶体结构和磁性。在整个溶液系列中，过硫化物（S $_2^{2-}$）单元中硫原子之间的距离几乎保持恒定。使用实验晶体结构作为输入的第一原理电子结构计算指出了这种恒定的S-S距离的重要性，有助于反键S-S能级钉扎费米能量。相反，假设的岩盐CoS不是一个好的半金属，尽管几乎是等结构和等电子的。我们利用我们对Co $_{1-x}$ Fe $_x$ S $_2$系统的理解，为新的铁磁半金属制定了一些规定。
The generic 1-bond:2-mode percolation type Raman signal inherent to the short bond of common (A,B)C semiconductor mixed crystals with zincblende (cubic) structure is exploited as a sensitive mesoscope to explore how various ZnSe-based systems engage their pressure-induced structural transition (to rock-salt) at the sub-macroscopic scale with a focus on ZnCdSe. The Raman doublet, that distinguishes between the AC- and BC-like environments of the short bond, is reactive to pressure: either it closes (ZnBeSe, ZnSeS) or it opens (ZnCdSe), depending on the hardening rates of the two environments un…
Metallic Bonding-Driven Elastic Softness and Optical Response in the Mg-Rich Laves-Phase LaMg2
Pabna Textile Engineering College, Bangladesh University of Textiles（帕尔纳纺织工程学院，孟加拉国纺织大学）；EcoBengal Centre for Materials and Energy Research（生态孟加拉材料与能源研究中心）；Bangladesh Atomic Energy Regulatory Authority (BAERA)（孟加拉国原子能监管局）；Department of Physics, University of Barishal（巴里萨尔大学物理系）；Department of Electrical and Mechanical Engineering, Nagoya Institute of Technology（名古屋工业大学电气与机械工程系）；School of Materials Science and Engineering, Faculty of Science, University of New South Wales（新南威尔士大学理学院材料科学与工程系）
The electronic and the optical properties of metallic nitride (MN) monolayers are studied using a DFT formalism. In most of these monolayers, the electron density of the metallic atoms is much higher than that of the nitride atoms, and ionic, covalent, and metallic bonds are found in M-N bonds, resulting in fascinating electronic and optical properties. The optical band gap is varied from almost $0.0$ to $3.0$~eV for the MN monolayers depending on the bond type between the metallic and the nitride atoms, as well as the contribution of the type of orbitals around the Fermi energy. The optical p…
How particular bonds form in quantum materials has been a long-standing puzzle. Two key concepts dealing with charge degrees of freedom are dimerization (forming metal-metal bonds) and charge ordering (CO). Since the 1930s, these two concepts have been frequently invoked to explain numerous exciting quantum materials, typically insulators. Here we report dimerization and CO within the dimers coexisting in metallic NaRu$_2$O$_4$. By combining high-resolution x-ray diffraction studies and theoretical calculations, we demonstrate that this unique phenomenon occurs through a new type of bonding, w…
Practical applications of nanocrystalline metallic thin films are often limited by instabilities. In addition to grain growth, the thin film itself can become unstable and collapse into islands through solid-state dewetting. Selective alloying can improve nanocrystalline stability, but the impact of this approach on dewetting is not clear. In this study, two alloys that exhibit nanocrystalline thermal stability as ball milled powders are evaluated as thin films. While both alloys demonstrated dewetting behavior following annealing, the severity decreased in more dilute compositions. Ultimately…
PbTaSe2 is a non-centrosymmetric topological semimetal. In this work we have explored the structural, elastic, mechanical, bonding, electronic, acoustic, thermal, and optical properties of PbTaSe2. The electronic bond structure calculations confirm semi-metallic character. Fermi surface topology shows both electron and hole sheets. The single crystal elastic constants reveal that PbTaSe2 is elastically stable. The compound is soft, brittle, and highly machinable at the same time. It also possesses very high level of dry lubricity. Various anisotropy indicators suggest that PbTaSe2 is elastical…
Experimentally resolving atomic-scale structural changes of a deformed glass remains challenging owing to the disordered nature of glass structure. Here, we show that the structural anisotropy emerges as a general hallmark for different types of glasses (metallic glasses, oxide glass, amorphous selenium, and polymer glass) after thermo-mechanical deformation, and it is highly correlates with local nonaffine atomic displacements detected by the high-energy X-ray diffraction technique. By analyzing the anisotropic pair density function, we unveil the atomic-level mechanism responsible for the pl…
The chemistry (composition and bonding information) of metallic glasses (MGs) is at least as important as structural topology for understanding their properties and production/processing peculiarities. This article reports a machine learning (ML)-based approach that brings an unprecedented "big picture" view of chemical bond strengths in MGs of a prototypical alloy system. The connection between electronic structure and chemical bonding is given by crystal orbital Hamilton population (COHP) analysis; within the framework of density functional theory (DFT). The stated comprehensive overview is …
Controlling magnetism of transition metal atoms by pairing with $π$ electronic states of graphene is intriguing. Herein, through first - principle computation we explore the possibility of switching magnetization by forming the tetrahedral $sp^3$ - metallic $d$ hybrid bonds. Graphene multilayers capped by single - layer cobalt atoms can transform into the $sp^3$ - bonded diamond films upon the hydrogenation of the bottom surface. While the conversion is favored by hybridization between the $sp^3$ dangling bonds and metallic $d_{z^2}$ states, such a strong hybridization can lead to the reorient…
The chemical bond is one of the most powerful, yet controversial concepts in chemistry, explaining property trends in solids. Recently, a novel type of chemical bonding has been identified in several higher chalcogenides, characterized by a unique property portfolio, unconventional bond breaking and sharing of about one electron between adjacent atoms. Metavalent bonding is a fundamental type of bonding besides covalent, ionic and metallic bonding, raising the pertinent question, if there is a well-defined transition between metavalent and covalent bonding. For three different pseudo-binary li…
Single crystals of Sc5Rh6Sn18 were grown from Sn-flux. The crystal structure (SG: I41/acd, a = 13.5529(2) Å, c = 27.0976(7) Å) was studied by high-resolution X-ray diffraction on powder and single crystal material as well as by TEM. All methods confirm it to crystallize with Sc5Ir6Sn18 (space group I41/acd) type of structure. The performed structural studies suggest also the presence of local domains with broken average translational symmetry. Analysis of the chemical bonding situation reveal highly polar Sc2-Sn1, Sn-Rh and Sc2-Rh bonds, two- and three-center bonds involving Sn-atoms as well a…
