First-Principles Calculations on the Crystal/Electronic Structure and Phase Stability of H-Doped SrFeO₂

Abstract

It has been recently reported that H-doping of SrFeO 2 induces an insulator-to-metal transition but generates only a small amount of carrier electrons. To investigate the crystal structure of H-doped SrFeO 2 (SFOH) and the origin of its peculiar transport properties, we performed DFT-based first-principles calculations. Through structural sampling and total energy calculations, we showed that the doped hydrogen atoms exist in hydride form (H − ). Incorporation of the hydride drastically changed the valence state or the d-band configuration of the Fe ions adjacent to the doped hydride, resulting in a metallic density of states in specific hydride configurations. Thermodynamic analysis revealed that the formation of an insulating phase with O-site hydride was energetically preferable, but metallic phases with O-site hydride or interstitial hydride could also be present at reaction temperature, suggesting that SFOH is a mixture of an insulating matrix and metallic domains. This two-phase model accounted for the observed low carrier density as well as the metallic transport properties.