Electronic and dielectric properties of insulating Zr3N4 -: art. no. 235106

The electronic structures and dielectric functions of Zr3N4 were studied by a first-principles density-functional method. Three different structure models were used: (1) ZrN in a rocksalt structure with an ordered Zr vacancy, or Zr(3)squareN(4), (2) c-Zr3N4 in the cubic spinel structure and (3) o-Zr3N4 in the orthorhombic structure. All three structures of Zr3N4 are found to be insulators with small indirect band gaps. This appears to be consistent with experimental observation that Zr3N4 is an insulator. Total-energy (E) calculations show that Zr(3)squareN(4) has an expanded lattice constant compared to ZrN by about 0.75%, and that E(Zr(3)squareN(4))<E(o-Zr3N4)<E(c-Zr3N4) which indicates that the ordered defect model for Zr3N4 is valid. It is further demonstrated that past calculations showing Zr(3)squareN(4) to be a metal were caused by the failure to relax the vacancy structure. The electronic structures and the optical dielectric functions for all three models were calculated and analyzed in detail. The Zr(3)squareN(4) model again shows the best overall agreement with available experimental data. All three structures have relatively large optical dielectric constants at zero frequency. Possible implications from these calculations are discussed.