Theoretical design of superconducting electrides

Realizing the coexistence of multiple states such as electride, metallicity, and superconductivity in a compound is of great interest from basic research and practical application. Most of the electrides exhibit semiconducting or insulating properties under high pressure due to the strong localization of both interstitial and orbital electrons. We propose that the application of pressure and variable chemical composition becomes an effective way to achieve this goal. Three hitherto unknown electrides (Li₅P, Li₆P, and Li₈P) with superconductivity are identified through first-principal swarm structural search. More intriguingly, C2/c Li₆P exhibits a T_c of 39.3 K at 270 GPa, which is the highest among the already known electrides. On the other hand, we found that modifying the chemical composition, in these electrides, can not only modulate the magnitude and distribution of interstitial electrons of electrides but also have great effect on superconductivity. We also apply this strategy to lithium selenides or tellurides. More interestingly, their Li-rich compounds can achieve superconductivity at much lower pressure in comparison with lithium phosphide.