CHEMICAL BONDING IN STOICHIOMETRIC AND SUBSTOICHIOMETRIC VANADIUM NITRIDE

A band structure calculation is performed for VN and VN0.75 assuming long-range ordered vacancies at the nonmetal lattice sites in the latter system. Chemical bonding is discussed in terms of total, partial, and differential density of states. Crystal orbitals are visualized by means of molecular orbital cluster calculation. Strong sigma and pi chemical bonds are enabled across the vacancy by removing N atoms. The metal-metal bond is strengthened and the metal-nitrogen bond is weakened in the vacant system. The extreme hardness and unusual thermal behavior are in good agreement with the picture of the conjugated system of pi bonds interconnected in three dimensions. (C) 1994 Academic Press, Inc.