Pressure-Stabilized Ir3– in a Superconducting Potassium Iridide

Abstract

The first charge-separated iridide (Ir3–) in an extended solid was identified at elevated pressure when combined with potassium. According to an unbiased structure searching method that combines first-principles calculations with particle swarm optimization algorithms, K3Ir in the Cu3Ti-type structure shows a favorable formation enthalpy (ΔH) compared to the elements and is dynamically stable above 10 GPa. This novel semiconductor (Eg ≈ 1.6 eV) has sufficient orbital separation to allow complete charge transfer from K to Ir, and Bader charge analysis supports the formation of a formally anionic Ir3–. Further, electron doping of K3Ir through Pt substitution makes the system metallic, and electron–phonon coupling calculations indicate that K3(Ir0.875Pt0.125) falls in the strong-coupling regime, with a predicted superconducting transition temperature (Tc) of ∼27 K at 20 GPa. These results suggest that systems containing elements isoelectronic with classical BCS superconductors such as mercury might have an i...