Pressure-Stabilized Ir3- in a Superconducting Potassium Iridide

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 (OH) compared to the elements and is dynamically stable above 10 GPa. This novel semiconductor (E-g approximate to 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 K-3(Ir08.75Pt0.125) falls in the strong-coupling regime, with a predicted superconducting transition temperature (T-c) of similar to 27 K at 20 GPa. These results suggest that systems containing elements isoelectronic with classical BCS superconductors such as mercury might have an increased probability of exhibiting a superconducting transition.