Phase transition and electronic properties of skutterudite-type IrP under high pressure.

Binary skutterudite-type IrP3 possesses a unique structural configuration that exhibits unusual electronic, thermoelectric, and dynamical properties and can be applied in thermoelectric generators; IrP3 has unique square (P4) rings stacked with a relatively loose arrangement and thus has been expected to exhibit fascinating evolution in the bonding patterns and electronic properties under high pressure. Herein, we systematically investigated the global energetically stable structures of IrP3 under ambient- and high-pressure conditions using the swarm intelligence-based structure searching technique in combination with first-principles calculations. Our theoretical prediction shows that the skutterudite-type structure with the Im3[combining macron] symmetry is most stable under ambient conditions. An orthorhombic structure with the Pmma space group was predicted to be energetically superior to the Im3[combining macron] phase above 47.60 GPa. The abrupt volume collapse at the corresponding phase boundaries even reached 14.67%, stemming from the abrupt collapse of large voids in the Im3[combining macron] phase. To explore the possibility of the occurrence of pressure-induced metallization and superconducting states under compressive conditions, the electronic band structures were investigated. Our results showed that the Im3[combining macron] phase was a narrow-gap semiconductor with the band gap of 1.04 eV, whereas the high-pressure Pmma IrP3 was a metallic phase with the superconducting transition temperature of 2.40 K. The current results are beneficial for the further understanding of other skutterudite-type compounds under high pressure.