Ab-Initio Studies of the Stability and Electronic Properties of Borides of Metals. II. Diborides of 4d- and 5d-Metals

摘要

The self-consistent full-potential LMTO method is used to study the electron energy properties of diborides of some 4d- and 5d-metals (Y, Zr, Nb, Mo, Tc, Ru; La, Hf, Ta, W, Re, Os) with the AlB_2-type structure. The chemical stability and the regularities of the properties of series of isostructural borides depending on the nature of the metallic sublattice are analysed on the basis of the band structure parameters and calculated cohesive energies. Direct non-empirical computations of the energies of particular bonds (M-M, M-B, B-B) are carried out for the most stable MB_2 phases (M = Ti, V, Zr, Nb) as an example. It is found that the changes in cohesive characteristics of the diborides are controlled by the energy of covalent bonds M-B. For the system Re-B, the first principle analysis of the energy stability of two crystallographic modifications of ReB_2 is performed and the nature of the chemical bonding in D_(6h)~4-ReB_2 is discussed.