ELECTRONIC-STRUCTURE OF EPSILON-TI2N AND DELTA'-TI2N

Self-consistent band structure calculations have been performed for the antirutile structure of epsilon-Ti2N and for the metastable long-range ordered defect structure of delta'-Ti2N. In accordance with recent neutron diffraction data a relaxation of the Ti atoms in direction of the crystallographic c-axis away from the vacancies was assume-d. Band structures, densities of states, partial local densities of states and charge density contour plots are discussed with regard to the chemical bonding in these compounds. On the basis of the band structure data, a qualitative explanation for the occurrence of the metastable long-range ordered delta'-phase in the Ti-N(x) system near a composition x = 0.5 and for the high stability of the epsilon-phase can be given. Contrary to hypothetically ordered TiN0.75, no so-called vacancy states with sigma bonding of Ti e(g)-like states across the vacancies are found for delta'-Ti2N.