Dynamically Forming Electrides Based on Ionic Conductors: Physicochemical Foundations, Nanoengineering, and Prospects

In modern science, the field of electrides has emerged as a highly active research frontier. An intense surge of interest in these materials—phases with high concentrations of anionic electrons—is driven by their promise for vast applications and unique properties. Non-stoichiometric electrides—materials hosting interstitial electron densities exceeding those in F-centers—remain scarce. Traditional computational screening relies on idealized static structures at 0 K, overlooking such materials. Here, we overcome this limitation by introducing a nanoionics paradigm in the field. Dynamically forming non-stoichiometric electrides arise under thermodynamically favorable conditions (ΔG < 0) in non-equilibrium nanosystems based on silver/copper halide solid-state ionic conductors. We demonstrate that stable electride phases form when the ionization potential of mobile host cations exceeds that of incident guest metal atoms; the core descriptor of these processes is φMH − φMG = ΔφHG > 0. The resulting materials exhibit carrier densities exceeding 1021 cm−3—well above the Mott degeneracy criterion—consistent with degenerate Fermi liquid behavior, pending direct transport confirmation. These materials remain stable in vacuum or inert gas at ambient pressure. This work establishes a generalizable framework for expanding the chemical space of electrides beyond the traditional field and creates synergy between the domain of electrides–berthollides and solid-state ionics/nanoionics/spintronics.