The influence of lattice vacancies on the structural, cohesive, and electronic properties of Nb and Mo borides were examined by means of the full-potential linearized augmented plane wave method and the generalized gradient approximation. The structural parameters, densities of states, charge distribution, heats of formations, and vacancy formation energies for metal-deficient hexagonal Nb1–xB2, Mo1–xB2 as well as for B-deficient rhombohedral Mo2B5–y were obtained and compared with those for complete hexagonal NbB2, MoB2 and rhombohedral Mo2B5. It was shown that the presence of metal vacancies in hexagonal phases led to: a decrease in the in-plane parameter, a, but an increase in the interplane cell parameter, c; to pronounced changes in the near-Fermi densities of states and the appearance of novel vacancy states; and to a considerable decrease in the stability of borides. In the case of Mo2B5, the appearance of B vacancies led to enhancement of the stability of a rhombohedral phase.

Influence of Lattice Vacancies on the Structural, Electronic and Cohesive Properties of Niobium and Molybdenum Borides from First-Principles Calculations. I.R.Shein, A.L.Ivanovskii: Physical Review B, 2006, 73[14], 144108 (9pp)