Pressure-induced electrides and metallic phases in the Y-Cl system

Pressure can profoundly change the electronic structure, leading to the formation of new phases and materials with exotic properties. Herein, using evolutionary algorithms and density functional theory, we systematically investigate the behaviour of materials in the yttrium-chlorine binary system under pressure. Electrons are found to be spatially confined at low pressures in yttrium chlorides and tend to form new electrides. In particular, a novel yttrium chloride, Y₃Cl₂, is predicted to be thermodynamically and lattice dynamically stable at approximately 10 GPa. Further analyses of the electron localization function and partial charge density identify trigonal Y₃Cl₂as a new 2D high-pressure electride with partially localized electrons contributing to the conduction. By further increasing the pressure, electrons in the yttrium-chlorine binary system tend to delocalize with the electrides decomposing into two new compounds (Y₂Cl and YCl₂) and a new YCl phase (space groupP6₃/mmc) above 20 GPa. These newly discovered phases are all metallic in their stable pressure range according to band structure simulations without interstitial electron localization. The discovery of these unconventional yttrium chlorides may inspire strategies to search for low-pressure electrides in other rare-earth halogenide systems.