The First Principles Study Of The Stability For Transition Metal Diborides (0001) Surfaces

In modern industry, boron and boron compounds are widely used in all sectors of our economic developing. Boron compounds mostly have high temperature, wear, and many unique physical and chemical properties. With the discovery of Super-conductingcritical transition temperature (Tc)39K of magnesium diboride(MgB2) caused great concern in physics. A1B2-metal borides with good physical and chemical properties, such as high hardness, high melting point, high antioxidant capacity, semi-metallic, excellent electrical conductivity, that aroused extensively interesting. Especially in2011graphite won the Nobel Prize in Physics, people had interested in graphene-like boron layer. However, due to the lack of boron sp2orbital electron is difficult to form single-layer graphenesheet structure of boron, so instead of researching borides bulk and surface properties.In this paper, we calculated diboride crystals and (0001) surfaces by first-principles, and discussed (0001) surface geometric and electronic properties by first-principles. All calculations under the generalized gradient approximation plane wave ultrasoft-pseudopotential method, calculated the total energy and the lattice geometry is optimized to be the ground state equilibrium model. The crystal (0001) surface’s geometry relaxation, the band structure, density of states, sub-state density, electron population, different electron density, surface energies calculation and analysis are based on this model, the main research contents and results are as follows:(l)Optimized structure based on the calculation and analysis of the ideal two boride crystal band structure and density of states. By the band structure and density of states analysis, the ideal crystal of MB2in no band gap at the Fermi level. That bulk showed well metallic properties, this is well electrical property. Analysis the different diborides chemical stability by density of states, MB2(M=Sc, Y, V, Nb, Cr, Mo) these types of compounds, Wocc/Wb value of NbB2is most closed to1, so NbB2has the highest chemical stability in the MB2(M=Sc, Y, V, Nb, Cr, Mo) compounds. (2)For MB2(M=Sc,Y, V, Nb, Cr, Mo)(0001) surfaces by the first-principles calculations show that:First, the surfaces electronic redistribution can only achieve a more stable structure after full relaxations. There are different changes after relaxations for MB2(0001) surfaces, but the relaxation is mainly concentrated in the top three atomic layers. When the atomic layer level reached to7, atomic relaxation is converged. Second, according to the surface energies, III group metal diborides (0001) surfaces of metal terminated surfaces are more stable than boron terminated surfaces; V group metal diborides surfaces of boron terminated surfaces are more stable; VI group metal diborides surfaces are stable at boron terminated surfaces for great range chemical potential of boron, the metal from group III to VI group metal, diborides surfaces is more stable at boron terminated surfaces with increasing the percentage of surface stability.