Xiaoguang Luo

First-principles study of B2CN crystals deduced from the diamond structure

An assumed B2CN crystal system containing seven possible diamond-structured configurations in boron-carbonitride B–C–N compounds has been studied by using an ab initio pseudopotential density functional method. After structural relaxation, the lattice constant, bulk modulus and shear modulus, and electronic band structures as well as the electron density of states are calculated for the derived B2CN structures. A unique type t-B2CN phase deduced from the diamond structure contains only B–N and B–C bonds in a tetragonal cell, and it has the lowest total energy and an electron-deficiency structure with non-vanishing density of states at the Fermi energy. Unlike diamond and c-BN, the t-B2CN phase may show metallicity.

The atomic structures of carbon nitride sheets for cathode oxygen reduction catalysis.

Carbon nitride sheets are promising Pt replacement materials for cathode oxygen reduction catalysis. Using first principles calculations with a global optimization method, we search for the most stable structures of the monolayer carbon nitrides at various C:N ratios. The results show that the larger the ratio, the more energetically favorable the obtained structures, and the more preferably for the C, N atoms to assume sp(2) configurations. A volcano shape is revealed for the curve of the representative O2 adsorption energies on the sheets vs. the ratios. In the ratio range of 2.0-3.0, the sheets not only have lower formation energies than the stable graphitic-C3N4, but also can potentially catalyze the oxygen reduction as efficiently as Pt.

Prediction of graphitelike BC4N from first-principles calculations

We present first-principles calculations of the structural and electronic properties of possible graphitelike BC4N constructed from 3r-graphite structure. Our calculation results show that the hexagonal BC4N structure stacked with one B-N layer and two C-C layers has the lowest total energy among all constructed BC4N structures. The calculated negative formation energy indicates that it may be synthesized from 3r-graphite and 3r-BN. Its stability has been further confirmed by mechanical stability criteria. The electronic properties show that it is a narrow band gap semiconductor.

Ground-state properties and hardness of high density BC6N phases originating from diamond structure

We report two possible metastable high density BC6N phases originating from the diamond structure. The ground-state properties of the BC6N phases are calculated using first-principles density-functional methods and the Vickers hardness is estimated using a semiempirical microscopic model. The calculated results show that two BC6N phases are semiconductors with Vickers hardness about 79–80GPa, indicating that the zinc-blende-like BC6N compounds are superhard material and have larger hardness than cubic BC2N and cubic boron nitride.