Pressure-induced structural transition and superconductivity in hard compound IrB4.

The recent discovery of MoB₂ with a superconducting transition temperature (T_c) of up to 32 K at 100 GPa provides new insights into the metallization and subsequently high-T_c superconductivity of diborides, highlighting the potential of transition metals in these compounds. We herein re-evaluated the structure, mechanical, and superconducting properties of IrB₄ under pressure up to 300 GPa using first-principles. Our calculations reveal that a new P2₁/c phase exhibiting a hardness of 15.75 GPa surpasses the stability of the C2/m structure identified through the particle swarm optimization at ambient pressure. Upon compressing, the P2₁/c phase transforms into an MgB₂-type structure with a space group of P6₃/mmc at 62.5 GPa and then into the orthorhombic Cmca phase above 109 GPa. Unlike semiconductor behavior of the atmospheric pressure phase, the two high-pressure structures are metallic and superconducting, with T_c values of 29.90 for P6₃/mmc at 62.5 GPa and 13.45 K for Cmca at 125 GPa. Analysis of the electronic structure and electron–phonon coupling (EPC) reveals that the high T_c, similar to MgB₂-type MoB₂, stems from the Van Hove Singularities (VHS) near the Fermi level donated by transition metal Ir. The effect further enhances the EPC based on the boron contribution. More interestingly, pressure has little impacts on the position of the VHS. These findings provide a new platform for designing advanced high-T_c superconductors. [ABSTRACT FROM AUTHOR]