Insight into the vacancy effects on mechanical and electronic properties of V5Si3 silicides from first-principles calculations

As so far, the development and application prospects of transition metal silicon-based materials have received the considerable attention. V-Si silicides are one of the most important silicon-based high-temperature materials. Brittle behavior hinders their wide application. In present work, the influence of vackancies on mechanical properties, brittle/ductile behavior and electronic properties of V₅Si₃ silicides is studied using the first-principles calculations. The vacancy formation energy, elastic constants, elastic modulus, brittle/ductile behavior and electronic behavior of the perfect V₅Si₃ and V₅Si₃ with vacancies were comparatively calculated and discussed, respectively. The thermodynamic data and phonon frequencies demonstrate that the V₅Si₃ with different vacancies can exhibit the structural stability. Although the vacancies weaken the hardness of V₅Si₃, the vacancies improve the brittle behavior of the parent V₅Si₃. Especially, the Si_-Va1 and Si_-Va2 vacancies in V₅Si₃ induced brittle-to-ductile transition for V₅Si₃ desilicides. The electronic structures explain the mechanism of the difference of mechanical properties for different vacancies.

Transition metal silicide surface grafting by multiple functional groups and green optimization by mechanochemistry

Chromium disilicide (CrSi2) particles were synthesized by using an arc melting furnace followed by mechanical milling. XRD and DLS analyses show that aggregates of around 3 μm containing about 10 nm sized crystallites were obtained. These aggregates were functionalized in solution by coupling agents with different anchoring groups (silane, phosphonic acid, alkene and thiol) in order to disperse them into an organic polymer. Dodecene was used to modify the CrSi2 surface during mechano-synthesis in a grinding bowl with quite little solvent quantity and the optimization step allowed the aggregate size to be reduced to 500 nm. A thermoelectric composite was then made of alkene CrSi2 grafted samples and poly(p-phénylène-2,6-benzobisoxazole). This study opens the route for new surface grafting of intermetallic silicides for applications linked to electronics and/or energy.

Electronic and Magnetic Properties of Bulk and Monolayer CrSi2: A First-Principle Study

We investigated the electronic and magnetic properties of bulk and monolayer CrSi2 using first-principle methods based on spin-polarized density functional theory. The phonon dispersion, electronic structures, and magnetism of bulk and monolayer CrSi2 were scientifically studied. Calculated phonon dispersion curves indicated that both bulk and monolayer CrSi2 were structurally stable. Our calculations revealed that bulk CrSi2 was an indirect gap nonmagnetic semiconductor, with 0.376 eV band gap. However, monolayer CrSi2 had metallic and ferromagnetic (FM) characters. Both surface and confinement effects played an important role in the metallic behavior of monolayer CrSi2. In addition, we also calculated the magnetic moment of unit cell of 2D multilayer CrSi2 nanosheets with different layers. The results showed that magnetism of CrSi2 nanosheets was attributed to band energy between layers, quantum size, and surface effects.

Crystal Structure, Stability, and Physical Properties of Metastable Electron-Poor Narrow-Gap AlGe Semiconductor

We report for the first time the full crystal structure, the electronic structure, the lattice dynamics, and the elastic constants of metastable monoclinic AlGe. In addition to ultrarapid cooling techniques such as melt spinning, we show the possibility of obtaining monoclinic AlGe by water-quenching in a quartz tube. Monoclinic AlGe and rhombohedral Al₆Ge₅ are competing phases with similar stability since they both begin to decompose above 230 °C. The crystal structure and electronic bonding of monoclinic AlGe are similar to those of ZnSb and comply with its 3.5 valence electrons per atom: besides classical two electron-two center Al-Ge and Ge-Ge covalent bonds, Al₂Ge₂ parallelogram rings are formed by uncommon multicenter bonds. Monoclinic AlGe could be used in various applications since it is found theoretically to be an electron-poor semiconductor with a narrow indirect energy bandgap of about 0.5 eV. The lattice dynamics calculations show the presence of low energy optical phonons, which should lead to a low thermal conductivity.