Potential existence of post-perovskite nitrides; DFT studies of ThTaN3

Within density functional theory, the equations of state for cubic perovskite (c-pv) and hypothetic orthorhombic perovskite (o-pv GdFeO3-type) and post-perovskite (ppv) forms of ThTaN3 are obtained. The decreasing volume and stabilizing energy indicate pressure enabled transitions: c-pv →o-pv →ppv. From electronic structure analysis the chemical system is found insulating in the c-pv ground state form with ∼1eV band gap and semi-conducting for the ppv due to increased covalence. The chemical bonding properties show that Th and Ta bondings with the 2 N sites are selectively differentiated and reinforced for Ta–N bond within ppv form. This is the consequence of the corner as well as edge sharing octahedra characterizing ppv while pv structures have only corner sharing octahedra. It is the first case of potential post-perovskite nitride.

ThTaN3: Projected charge density (for 4 fu) onto basal plane: (a) cubic perovskite, (b) orthorhombic perovskite and (c) post-perovskite. Red, green and blue areas are relevant to strong, medium and low localization of density.Figure optionsDownload full-size imageDownload as PowerPoint slide