This article investigated the low-energy structures of Al6NamC (m = 2, 4, 6, 8) clusters and their electronic structures by using genetic algorithm combined with density functional theory and configuration interaction methods. The computations show that the C atoms prefer sitting at the center, whereas the Na atoms tend to locate at the outside of the clusters. The valence molecular orbitals (MOs) agree well with the prediction of the jellium model. The stronger attraction of the central carbon to the valence electrons will depress the potential energies locally, which makes the 2S level go obviously lower and the 2P and 1D orbitals form a sub-band. The 26 valence electrons in Al6Na4C form closed 1S21P62S21D102P6 shells and correspond to a new magic structure. The MOs and electron localization function show that the sodium cores are exposed at the outside of the valence electrons and form naked cations. The contraction of the valence electrons because of the carbon doping enhances the charges on the Al6C moieties, and the Na+ cores on the peripheries are ionically bonded to the Zintl anions (Al6C)q−. The Al6Na4C has a tetrahedral structure with symmetry Td, and it may be used as building blocks to synthesize Zintl solid. 相似文献
In this study, a simple one-pot method was adopted to synthetize Pd/Pt core/shell nanostructures with truncated-octahedral morphology. The morphology of the obtained Pd/Pt nanoparticles was characterized by transmission electron microscopy (TEM) and high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). In addition, the composition was determined by energy-dispersive X-ray spectroscopy (EDS) and inductively coupled plasma atomic emission spectroscopy (ICP-AES), and the electric structures were studied by powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Based on the above results, it could be noticed that Pd/Pt core/shell nanostructures with truncated-octahedral morphology were produced, where the core consisted of Pd atoms and the shell consisted of Pt atoms. In order to test the catalytic properties of the prepared Pd/Pt nanoparticles, cyclic voltammetry (CV) was carried out in 0.5 M H2SO4 and 0.5 M H2SO4 + 1 M HCOOH. Compared with commercial Pt black, the Pd/Pt core/shell nanostructures with truncated-octahedral morphology exhibited higher activity and stability toward formic acid oxidation.
By using genetic algorithm combined with B3LYP and QCISD methods, this paper investigates the stabilities and electronic structures of Al6OMm (M?=?Na, K; m?=?2,4,6) and a few other AlnXNam (X?=?C, N, O) clusters. The results show that the nonmetal doped metal clusters with 26 valence electrons have enhanced stabilities and large energy gaps. This paper extends the Jellium model for the application to the nonmetal doped metal clusters and explains the electronic origin of this strong magic structure. The nonmetal X atom is situated in the centre of the magic clusters. The 2s/2p orbitals of the central atom interact strongly with the superatomic 1S/1P orbitals and form bonding and antibonding orbitals. The bonding orbitals make the C/N/O atoms form s2p6 shell closure, and the antibonding orbitals make the metal moieties form closed 2S22P6 shells. The 26 valence electrons form closed s2p6S2P6D10 shells, and this electronic configuration can be taken as the combination of the octet rule and 18-electron rule. The octahedral Al6O2? core is a superatomic anion with great stability, and it can be used as building blocks to assemble Zintl phase materials by interaction with alkali metals. 相似文献
Methods are described for making reproducible and robust vanadate-glass threshold switches both by a bulk and a thick-film technique; the latter method lendsitself to the large-scale production of the devices. The electrical characteristics obtained using dc, sine-wave and square-wave inputs are described and the various electrical parameters such as: threshold voltage, holding current, delay time, etc. are given. The results of a statistical analysis involving 30 alumina substrates with 12 switches on each are described, the population being analysed in terms of the standard deviation and mean deviation of the dc threshold voltage and the resistance of the off-state. An attempt is made to correlate the variation in parameters from device to device with variables involved in the furnace-firing schedule as well as the printing. 相似文献