Theoretical Studies On Prediction Of Structure And Physical Properties Of Iridium Phosphides Under High Pressure

High Pressure is a fundamental thermodynamic variable that can be used to control the properties of materials and generate new structures not accessible at ambient conditions.Iridium-phosphor(Ir-P)compounds are attracting many attentions due to their attractive electronic properties and extensive industrial ap-plications.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 function-al theory,the hitherto unknown binary Ir-P phase diagram was investigated in a wide pressure range with various chemical compositions.At ambient pressure,the current thermodynamic calculations authorized that the previous well confirmed Ir2P-Fm3m,IrP2-F21/c and IrP3-Im3-are stable.In particular,two novel phases of IrP-P4/nmm and IrP2-I41/amd were discovered at high pressure.The current theoretical phonon dispersion curves and phonon density of states(PHDOS)have evidence of the absence of any imaginary dynamical vibration in the whole Brillouin zone for the novel high-pressure IrP-P4/nmm and IrP2-I41/amd structures.Meanwhile,the two phases have been demonstrated to posses a metallic char-acter.The DOS at Fermi level consists primarily of iridium d states with moderate mixing with the phosphorus p states.We also calculated the electron localization function(ELF)data,which clear-ly shows the formation of the bonding feature in the predicted novel high-pressure phases.To accommodate the electrons,mixtures of covalent and polar covalent bonds exit in the two phases.Based on the Bader change analysis,electrons trans-ferred from P site to Ir site in the two phase.For the IrP-P4/nmm structure,there are a total 0.115 electrons transferred from P site to Ir site.There are a total 0.18 electrons transferred from P site to Ir site in the IrP2-I41/amd phase.The two phases are all mechanically stable by the calculation of elastic constants.The IrP-P4/nmm structure has good malleability,and the IrP2-I41/amd has preferable brittleness.The present results are expected the understanding of the structure and elec-tronic properties of Ir-P system under high pressure and further enrich the transition metal phosphides chemistry.