Theory and Discovery of Electride Materials

Electrides are materials with electrons localized at interstitial regions of the crystal lattice that act as anions. These materials are promising candidates for applications in, e.g., catalysis, electron emission, and superconductivity.

Despite the discovery of a number of electride materials in the past decade, there is neither a general-purpose experimental characterisation technique to determine whether a material is an electride nor is there a consensus on the theory of why some materials are electrides and exhibit interstitial electrons, particularly at ambient conditions.

In this work, a theoretical framework for the origin of interstitial electrons in electrides is presented. Applying this theory to prototypical systems demonstrates it can explain electride-like behavior in not only inorganic electrides but also high-pressure and organic electrides. Based on this theory, a descriptor is further developed and an electride figure of merit is defined that quantifies the likelihood of a system being an electride. Using first-principles simulations, we compute this descriptor to for approximately 52,000 materials in the Materials Project database to obtain a list of inorganic electride candidates and rank them based on their electride figure of merit.

Our results suggest that electride-like behavior may not be as rare as previously perceived, and provide a database that will help rationally prioritize future research and discovery of new electride materials.