Hydrogen-Induced Phase Transition and Emergent Properties in SrFeO_<i>x</i>

Abstract In recent years, ionic modulation, particularly hydrogen intercalation, has gained attention as a powerful method for tuning the properties of materials. Although the SrFeO x system is similar to SrCoO x , which can be protonated to the HSrCoO 2.5 phase, it remains a challenge for the hydrogenation of SrFeO 2.5 . In this study, starting from the perovskite SrFeO 3– δ , we achieved hydrogen intercalation and obtained stable hydrogenated brownmillerite-phase HSrFeO 2.5 via Pt-catalyzed H-spillover at room temperature. The results indicate that the hydrogenation process is accompanied by the simultaneous oxygen ionic release, that is, perovskite SrFeO 3– δ is the prerequisite for the hydrogen-induced phase transition. Subsequently, upon hydrogenation, the entire phase transition cycle among the perovskite SrFeO 3– δ , brownmillerite SrFeO 2.5 , and the hydrogenated HSrFeO 2.5 phase, is completed. Furthermore, SrFeO 3– δ exhibits a remarkable 9.4% lattice expansion, and its electronic state undergoes a multi-step evolution, transforming from a pristine helical antiferromagnetic insulator to a bad metal, eventually returning to an antiferromagnetic insulator. Based on the obtained results, we fabricated microscale patterns with varied surface morphologies and electrical conductivities that can be used in fabricating electronic devices. This study presents a novel approach for modulating the properties of correlated and functional materials.