Showing papers by "Siqi Shi published in 2010"

Ab initio studies on atomic and electronic structures of black phosphorus

Abstract: The atomic and electronic properties of black phosphorus (BP), which has been recently shown to have potential application as anode material for lithium ion batteries, are studied via ab initio calculations. The calculations reveal that the interlayer interaction in BP is Van der Waals Keesom force, which is critical to the formation of the layered structure. Interestingly, we also found that the small band gap of bulk BP (0.19 eV) when compared with that of single layer BP (0.75 eV) is partly because of the interlayer Van der Waals interaction in BP. The change in a materials band structure because of Van der Waals interaction is rarely reported in literature.

First-principles investigation on redox properties of M -doped CeO 2 ( M = Mn , Pr , Sn , Zr )

Abstract: The effects of $M$ $(M=\text{Mn},\text{Pr},\text{Sn},\text{Zr})$ doping on the redox thermodynamics of ${\text{CeO}}_{2}$ have been investigated using first-principles density-functional theory calculations with the on-site Coulomb interaction taken into account. Two different mechanisms for the O-vacancy formation in doped ${\text{CeO}}_{2}$ have been clarified. Compared with the case of pure ${\text{CeO}}_{2}$, the decrease in the O-vacancy formation energy for the Zr-doped ${\text{CeO}}_{2}$ is mostly caused by the structural distortion, whereas the decrease for Mn-, Pr-, or Sn-doped ${\text{CeO}}_{2}$ originates from the electronic modification as well as from the structural distortion. It is found that the electronic modification occurs in those dopants whose uttermost atomic orbitals are half or fully occupied by the filling of the excess electrons left by the formation of the O vacancy. Two effects also contribute to concentration dependence of the O-vacancy formation energies for different dopant species.

Electronic structures of fully fluorinated and semifluorinated zinc oxide sheets

Abstract: Using first-principles calculations, we investigate the structural, electronic, and magnetic properties of fully fluorinated and semifluorinated ZnO sheets. We find the fully fluorinated ZnO sheet prefers a twist-chair conformation, which is a nonmagnetic semiconductor. While for the semifluorinated sheet, the F-center conformation is the most stable and exhibits half-metallic behavior. The half-metallicity is attributed to the decrease in the charge transfer from Zn to O atoms after fluorination, which leads to the partial occupancy of the O 2p orbitals and spin-polarization in the semifluorinated sheet. Our studies demonstrate that fluorination is an efficient route to tune the electronic structures of ZnO nanostructures.

Layered Bi2Ca3Co2O9 composite as anode material for lithium-ion battery

Abstract: Polycrystalline and single crystalline composites of Bi2Ca3Co2O9 have been prepared by the conventional solid-state reaction and flux method, respectively. X-ray powder diffraction exhibits single pure phase and characterization of c-axis orientation. Plate-like grains parallel to the hot-forging direction are observed using scanning electronic microscopy. Electrochemical measurement shows that lithium ions can be intercalated/deintercalated Bi2Ca3Co2O9 with relatively large capacity, which displays its potential as a candidate of anode material for a lithium-ion battery.