Electronic structure, bonding, and ground-state properties of AlB_{2}-type transition-metal diborides

Abstract

The electronic structure and ground state properties of ${\mathrm{AlB}}_{2}$ type transition metal diborides ${\mathrm{TMB}}_{2}$ (TM=Sc, Ti, V, Cr, Mn, Fe, Y, Zr, Nb, Mo, Hf, Ta) have been calculated using the self consistent tight-binding linear muffin-tin orbital method. The equilibrium volume, bulk moduli ${(B}_{0}),$ pressure derivative of bulk moduli ${(B}_{0}^{\ensuremath{'}}),$ cohesive energy ${(E}_{\mathrm{coh}}),$ heat of formation $(\ensuremath{\Delta}H),$ and electronic specific heat coefficient $(\ensuremath{\gamma})$ are calculated for these systems and compared with the available experimental and other theoretical results. The bonding nature of these diborides is analyzed via the density of states (DOS) histogram as well as the charge density plots, and the chemical stability is analyzed using the band filling principle. The variation in the calculated cohesive properties of these materials is correlated with the band filling effect. The existence of a pseudogap in the total density of states is found to be a common feature for all these compounds. The reason for the creation of the pseudogap is found to be due to the strong covalent interaction between boron p states. We have made spin polarized calculations for ${\mathrm{CrB}}_{2},$ ${\mathrm{MnB}}_{2},$ and ${\mathrm{FeB}}_{2}$ and found that finite magnetic moments exist for ${\mathrm{MnB}}_{2}$ and ${\mathrm{CrB}}_{2}$ whereas ${\mathrm{FeB}}_{2}$ is nonmagnetic.