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

Transition metal antimonides have good catalytic,energy storage and thermoelectric properties at ambient pressure.In order to further explore its potential applications,it is necessary to study its structure and phase transition behavior under high pressure,as well as the corresponding physical and chemical properties.Based on the results of swarm structure searching technique combined with density functional theory,we proposed the hitherto unknown Ir-Sb phase diagram in a wide pressure range with various chemical compositions.At ambient pressure,two stable structures are predicted in this thesis.They are the IrSb₃ structure with the space group Im3 and the IrSb₂ structure with the space group P21/c.Under high pressure,we find five novel high pressure structures,which are IrSb₂-P-421m IrSb₂-I4/mmm,IrSb-C2/c,IrSb-P-1 and Ir₂Sb-Pmmm structures.In order to clarify the dynamic stability of the five new high-pressure phases,the phonon dispersion curves reveal that these phases are all dynamically stable.The research results of the formation enthalpy show that they are all negative in the studied pressure range,which proves that they have thermodynamic stability.The electronic band and density of states（DOS）of five high pressure structures are studied to understand the electronic properties and chemical bonds between atoms.The calculation results of the band structure show that the conduction band and the valence band of the new high-pressure phases cross the Fermi surface,indicating that the five high pressure phases all exhibit metallic properties.The calculation results of the density of states show that the d orbital of Ir atoms and the p orbital of Sb atoms are mainly contributed at the Fermi level.In order to further clarify the characteristics of electronic bonding,the electronic localization function（ELF）is calculated,and the results show that there are covalent bonds,metal bonds and ionic bonds in the five high pressure structures.Bader change analysis shows that Ir atoms have strong electronegativity,and under the action of pressure,the charge transfers from Sb atoms to Ir atoms.Through the calculation of elasticity,Ir₂Sb-Pmmn structure has strong compression resistance,IrSb₂-I4/mmm structure has strong rigidity.Through the study of the binary iridium-antimony compounds system,the structural phase diagram of the Ir-Sb system has been shown.The electronic properties and chemical bonds of the new phases under high pressure are emphatically explored.