Phase stability and electronic structures of stoichiometric tantalum mononitrides

Using the density functional methods, we study electronic and structural properties of stoichiometric phases of tantalum mononitride (TaN). The e phase is found to be most stable, closely followed by the theta phase. Interestingly, we find that the cubic delta phase of the stoichiometric TaN undergoes a spontaneous distortion into a tetragonal structure. This is attributed to a Jahn-Teller type distortion that lifts degeneracy at the Fermi level. The electronic structures indicate that the largest carrier density is expected for delta-TaN while theta-TaN is close to a quasi-one-climensional conductor. (C) 2008 Elsevier B.V. All rights reserved.