Phase diagram and bonding states of Ir-P binary compounds at high pressures

Abstract

Binary Ir-P compounds have been considered as the excellent candidates for catalytic applications with high activity. However, the difficulties associated with synthesis with novel structures and chemical stoichiometry in general remain. Herein, using the swarm structure searching technique in combination with density functional theory, the hitherto unknown binary Ir-P phase diagram was investigated in a wide pressure range with various chemical compositions. In particular, two novel phases of IrP-P4/nmm and IrP2-I41/amd were discovered at high pressure. The phonon dispersion curves suggest that all these phases are dynamical stable. Our calculated electronic properties show that the mixture behavior of covalent, ionic and metallic bonds simultaneously exits in the novel two phases. The bond population shows a high delocalized metalloid electron between the P-P atoms in IrP-P4/nmm phase, while the sp3 hybridized present in the buckled 2D P-P chains in IrP2-I41/amd phase. The theoretical electronic band structures reveal pressure-induced electronic topological transitions in IrP-P4/nmm phase, while it is absent in other stoichiometry of Ir-P system. The current theoretical results enrich the crystal structures and chemical stoichiometry of the binary Ir-P system and benefit the further understanding of the corresponding physical and chemical properties.