Pauling had proposed that charge is transferred from the more electronegative atom to the less electronegative one during metallic alloying. An expression has recently been derived for the energy of the unlike atom-pair bond using that concept. In this paper, Pauling's view is further supported by showing that the electronegativity and valence differences between unlike atoms in binary metallic alloys are of the required magnitude and direction so as to bring the metallic radii ratio R_A/R_B by charge transfer to a value r_A/r_B for ideal packing in an intermetallic compound. It is also demonstrated that lattice parameters of intermetallic compounds belonging to several crystal structure types can be obtained with excellent accuracy from the length of the atom-pair bond.
FeAl-based MIL composites of various iron alloys were fabricated with an innovative 'multiple-thin-foil' configuration and 'two-stage reaction' strategy.
Towards a resolution of the longstanding controversy regarding the existence of Cu-Li intermetallic compounds, we extensively investigate the phase stability of Cu-Li intermetallics with various possible stoichiometries at zero temperature and pressure using a global structure searching method. It is found that Cu-Li intermetallics can exist stably at atmospheric pressure, and three stable intermetallics (Fmmm Cu1Li2, Fd m Cu2Li1 and P Cu7Li1,) are identified. Electronic structure analysis reveals that although the three stable phases are metallic, covalent Cu-Cu and ionic Cu-Li bonds are foun…
Theoretical investigation of structural, elastic, electronic and bonding properties of A-15 Nb-based intermetallic compounds Nb3B (B = Pt, Os) have been performed using first principles calculations based on the density functional theory (DFT). Optimized cell parameters are found to be in good agreement with available experimental and theoretical results. The elastic constants at zero pressure and temperature are calculated and the anisotropic behaviors of the compounds are studied. Both the compounds are mechanically stable and ductile in nature. Other elastic properties such as Pugh's ratio,…
Structural, elastic and electronic band structure properties of A-15 type Nb-based intermetallic compounds Nb3B (B = Os, Pt, Au) have been revisited using first principles calculations based on the density functional theory (DFT). All these show excellent agreement with previous reports. More importantly, electronic bonding, charge density distribution and Fermi surface features have been studied in detail for the first time. Vickers hardness of these compounds is also studied. The Fermi surfaces of Nb3B contain both hole- and electron-like sheets, the features of which change systematically a…
We study a cast Mg-4.65Al-2.82Ca alloy with a microstructure containing $α$-Mg matrix reinforced with a C36 Laves phase skeleton. Such ternary alloys are targeted for elevated temperature applications in automotive engines since they possess excellent creep properties. However, in application, the alloy may be subjected to a wide range of strain rates and in material development, accelerated testing is often of essence. It is therefore crucial to understand the effect of such rate variations. Here, we focus on their impact on damage formation. Due to the locally highly variable skeleton formin…
The discovery of quasicrystals 30 years ago challenged our understanding of order at the atomic scale. While quasicrystals possess long-range orientational order they lack translation periodicity. Structurally complex, yet crystalline intermetallics and (bulk) metallic glasses represent competing states of condensed matter among metallic phases, including peculiarities like the q-glass. Considerable progress has been made in their structure elucidation and in identifying factors governing their formation; comparatively less is known about their interrelation. Moreover, studies bridging the spa…
The microstructure of Mg-Al-Ca alloys consists of a hard intra- and intergranular eutectic Laves phase network embedded in a soft $α$-Mg matrix. For such heterogeneous microstructures, the mechanical response and co-deformation of both phases under external load are not yet fully understood. We therefore used nano- and microindentation in combination with electron microscopy to study the deformation behaviour of an Mg-3.68Al-3.8Ca alloy. We found that the hardness of the Mg$_2$Ca phase was significantly larger than the $α$-Mg phase and stays constant within the measured temperature range. The …
Within 4 different crystal structures, 2280 ternary intermetallic configurations have been investigated via high-throughput density functional theory calculations in order to discover new semiconducting materials. The screening is restricted to intermetallics with the equimolar composition TMX, where T is a transition metal from the Ti, V, Cr columns, Sr, Ba, Y and La, M an element from the first line of transition metals and X a sp elements (Al, P, Si, Sn and Sb), i.e. to a list of 24 possible elements. Since the calculations are done combinatorically, every possible ternary composition is co…
The structural electronic and optical properties of intermetallic compound MgRh were investigated by using the ab-initio technique from CASTEP code. In this study we have carried out the pseudo-potential plane-wave (PP-PW) method based on the density functional theory (DFT), within the generalized gradient approximation (GGA). Our calculated structural parameters and corresponding graphical values fit with other previous available experimental data and other theoretical observations. The calculated electronic band structure reveals metallic conductivity and the major contribution comes from Rh…
Chemical bonding in 2D layered materials and van der Waals solids is central to understanding and harnessing their unique electronic, magnetic, optical, thermal and superconducting properties. Here we report the discovery of spontaneous, bidirectional, bilayer twisting (twist angle ~ 4.5°) in the metallic kagomé MgCo6Ge6 at T = 100(2) K via X-ray diffraction measure-ments, enabled by the preparation of single crystals by the Laser Bridgman method. Despite the appearance of static twisting on cooling from T ~ 300 K to 100 K, no evidence for a phase transition was found in physical properties me…
Structural, elastic, electronic and optical properties of laves phase intermetallic compounds CaRh2 and LaRh2 prototype with MgCu2 are investigated by using the first principle calculations. These calculations stand on density functional theory (DFT) from CASTEP code. The calculated lattice parameters are consistent with the experimental values. The significant elastic properties, like as bulk modulus, shear modulus, Youngs modulus and the Poissons ratio are determined by applying the Voigt Reuss Hill (VRH) approximation. The analysis of Pughs ratio shows the ductile nature of both the phases.…
We investigate the structural, electronic, mechanical and elastic properties of two niobium based intermetallic compounds Nb3Be and Nb3Be2 by using the DFT based theoretical method. A good agreement is found among the structural parameters of both the phases with experimentally evaluated parameters. For both the phases metallic conductivity is observed while Nb3Be phase is more conducting than that of Nb3Be2 phase. Evaluated DOS at Fermi level indicates that Nb3Be2 phase is electrically more stable than Nb3Be phase. For both phases Nb-4d states is mostly responsible for metallic conductivity. …
Using molecular dynamics simulations with embedded atom model potential, we study structural evolution of ${\rm Cu_{64.5}Zr_{35.5}}$ alloy during the cooling in a wide range of cooling rates $γ\in(1.5\cdot 10^{9},10^{13})$ K/s. Investigating short- and medium-range order, we show that structure of ${\rm Cu_{64.5}Zr_{35.5}}$ metallic glass essentially depends on cooling rate. In particular, a decrease of the cooling rate leads to a increase of abundances of both the icosahedral-like clusters and Frank-Kasper Z16 polyhedra. The amounts of these clusters in the glassy state drastically increase a…
We have theoretically investigated the electronic properties of neutral and $n$-doped dangling bond (DB) quasi-one-dimensional structures (lines) in the Si(001):H and Ge(001):H substrates with the aim of identifying atomic-scale interconnects exhibiting metallic conduction for use in on-surface circuitry. Whether neutral or doped, DB lines are prone to suffer geometrical distortions or have magnetic ground-states that render them semiconducting. However, from our study we have identified one exception -- a dimer row fully stripped of hydrogen passivation. Such a DB-dimer line shows an electron…
We propose previously unknown allotropes of phosphorus carbide (PC) in the stable shape of an atomically thin layer. Different stable geometries, which result from the competition between sp2 bonding found in graphitic C and sp3 bonding found in black P, may be mapped onto 2D tiling patterns that simplify categorizing of the structures. Depending on the category, we identify 2D-PC structures that can be metallic, semi-metallic with an anisotropic Dirac cone, or direct-gap semiconductors with their gap tunable by in-layer strain.
Honeycomb structure has been frequently observed in two-dimensional (2D) materials. CuAu in the buckled honeycomb (BHC) structure has been synthesized recently, which is the first case of 2D intermetallic compounds. Here, the dynamical stability of 2D $AX$ in the BHC structure, where $A=$ Cu, Ag, and Au and $X$ is a metallic element in the periodic table, is systematically studied by calculating phonon dispersions from first-principles. Among 135 $AX$, more than 50 $AX$ are identified to be dynamically stable. In addition, (i) a relationship between the dynamical stability and the formation en…
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。
Magnetic States and Electronic Properties of Manganese-Based Intermetallic Compounds Mn$_2$YAl and Mn$_3$Z (Y = V, Cr, Fe, Co, Ni; Z = Al, Ge, Sn, Si, Pt)
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…
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…
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…
Third-generation photovoltaic (PV) materials combine many advantageous properties, including a high optical absorption together with a large charge carrier mobility, facilitated by small effective masses. Halide perovskites (ABX3, where X is I, Br or Cl) appear to be the most promising third-generation PV materials at present. Their opto-electronic properties are governed by the B-X bond. A quantum-chemical bond analysis reveals that this bond differs significantly from ionic, metallic or covalent bonds. Instead, it is better regarded as metavalent, since it shares approximately one p-electron…
The segregation of solute atoms to grain boundaries can have a large influence on the mechanical behavior of polycrystals, particularly in metallic alloys. An overview of 400 calculations of solute-induced changes in grain boundary cohesion from 77 separate studies quantitatively demonstrates that the majority of the variation in solute-induced changes in boundary cohesion is explained by simple bond-breaking arguments. This trend is robust to changes in crystal structure and computational methods. The secondary contributions to embrittlement from other mechanisms, such as atomic size effects …
Identifying the nature of magnetism, itinerant or localized, remains a major challenge in condensed-matter science. Purely localized moments appear only in magnetic insulators, whereas itinerant moments more or less co-exist with localized moments in metallic compounds such as the doped-cuprate or the iron-based superconductors, hampering a thorough understanding of the role of magnetism in phenomena like superconductivity or magnetoresistance. Here we distinguish two antiferromagnetic modulations with respective propagation wave vectors of $Q_{\pm}$ = ($H \pm 0.557(1)$, 0, $L \pm 0.150(1)$) a…
