Abstract
The transition-metal nitride , which consists of weakly bonded neutral slabs of closed shell ions, has structural and chemical similarities to other layered nitrides which have impressive superconducting when electron-doped: , , , with , 15.2 K and 16.5 K, respectively, for appropriate donor concentrations . These similarities suggest the possibility of being another relatively high nitride upon doping, with effects of structure and the role of specific transition-metal ions yet to be understood. We report first-principles electronic-structure calculations for stoichiometric using density-functional theory with plane-wave basis sets and separable dual-space Gaussian pseudopotentials. An indirect band gap of 0.8 eV was obtained and the lowest conduction band is primarily of character, similar to and . The two N sites, one in the Hf layer and another one in the Ba layer, were found to have very anisotropic Born effective charges (BEC): deviations from the formal charge are opposite for the two sites, and opposite for the two orientations (in plane, out of plane). LO-TO splittings and comparison of BECs and dielectric constant tensors to those of related compounds are discussed, and the effect of electron doping on the zone-center phonons is reported.
- Received 29 July 2010
DOI:https://doi.org/10.1103/PhysRevB.82.155125
©2010 American Physical Society