Polymorphic YTiGe Intermetallic Electride Created by Hydrogenation and Dehydrogenation

Electrides are emerging materials with unique structural features of a positively charged lattice framework and interstitial anionic electrons trapped in structural cavities, exhibiting exceptional functionalities. Thermodynamic and electronic stabilities of the electrides are mainly dominated by the existence of anionic electrons and their structural arrangements that are interdependent with the lattice frameworks. Different arrays of anionic electrons in a fixed chemical formula can provide unexpected properties but are hardly found in electrides. Here, we demonstrate the stable polymorphic forms of intermetallic YTiGe electride at ambient pressure via hydrogenation and subsequent dehydrogenation processes. We find that hydrogenation leads to a phase transition from the P4/nmm structured YTiGe electride to the I4/mmm structured YTiGeH_1.5 hydride. Importantly, it was experimentally confirmed that the I4/mmm structure was retained, even after complete dehydrogenation. Our theoretical calculations demonstrate that the anionic electrons are localized in both tetrahedral Y₄ and octahedral Y₂Ti₄ cavities, indicating that P4/nmm and I4/mmm structured YTiGe compounds are polymorphic electrides. This polymorphic YTiGe electride system shows distinct magnetic properties, where a higher magnetic moment is obtained in the I4/mmm structured YTiGe due to a higher concentration of quasi-atomic anionic electrons. These results accentuate hydrogenation-dehydrogenation processes for exploring polymorphic electrides as functional materials.