Semiconductors with a chiral crystal structure in group IVB transition metal pernitrides.

Group IVB transition metal (TM) nitrides rarely exhibit the semiconductor phase, except for TMN (TM = Ti, Zr, and Hf) compounds. In this study, using the calculations based on density functional theory, we report two chiral crystal structures, namely 321 and 321, of TMN, which are dynamically stable at ambient pressure. Unlike conventional metal phases of transition metal dinitrides, the 321 and 321 configurations exhibit intriguing semiconductor properties (with bandgaps of 1.076 eV, 1.341 eV, and 1.838 eV for TiN, ZrN, and HfN, respectively). The mechanism of metal-to-semiconductor transition from the 4/ to 321 phase is deeply explored by investigating their crystal structure and electronic structures. When hydrostatic pressure is applied from 0 GPa to 200 GPa, the bandgaps of the 321 phase of TiN, ZrN, and HfN exhibit a different response, which is related to the orbital contribution at the conduction band minimum (CBM) and valence band maximum (VBM) and the lattice constants. Furthermore, according to the calculated mechanical properties, 321 and 321 phases exhibit higher bulk and shear moduli than the semiconductor phases of c-ZrN and c-HfN in the corresponding systems.