Abstract
Density functional theory calculations are used herein to explore the hexagonal (HX) NiAs-like polymorphs of Zr(B,C,N) and compare them with the corresponding Zr(B,C,N) Hagg-like face-centered-cubic rocksalt (B1) phases. Although all predicted compounds are mechanically stable according to the Born–Huang criteria, only HX Zr(C,N) are dynamically stable according to ab initio molecular dynamics simulations and lattice dynamics calculations. HX ZrN emerges as a candidate structure with a ground-state energy, elastic constants, and extrinsic mechanical parameters comparable with those of B1 ZrN. Ab initio band structure and semiclassical Boltzmann transport calculations predict a metallic character and a monotonic increase in electrical conductivity with the number of valence electrons. Electronic structure calculations indicate that the HX phases gain their stability and mechanical attributes through Zr d–nonmetal p hybridization and broadening of the Zr d bands. Furthermore, it is shown that the HX ZrN phase provides a low-energy coherent interface model for connecting B1 ZrN domains, with significant energetic advantage over an atomistic interface model derived from high-resolution transmission electron microscopy (HRTEM) images. The ab initio characterizations provided herein should aid the experimental identification of non-Hagg-like hard phases. The results can also enrich the variety of crystalline phases potentially available for designing coherent interfaces in superhard nanostructured materials and in materials with multilayer characteristics.
