ABSTRACT
The unique properties of direct bandgap semiconductors make it important to search for semiconductors exhibiting this phenomenon in perovskite materials. In this study, we employed first-principles calculations to investigate the crystal structures, magnetic configurations, and electronic properties of hexagonal perovskite BaMnO3 in its 4H and 6H phases. The results indicate that both structures exhibit antiferromagnetic characteristics, in which the Mn-O-Mn superexchange plays the dominant role in the 4H phase, although there is a competition between the Mn-Mn direct exchange interaction and the Mn-O-Mn superexchange interaction. In contrast, these two interactions exhibit harmonious coexistence in the 6H phase, and the two antiferromagnetic transitions occurring in the experimental phase should be related to the synergistic effect between them. Despite their different internal arrangements, they exhibit the same charge combination of Ba2+Mn4+O2-3. More importantly, both phases exhibit semiconductor properties with a direct bandgap, making it suitable to serve as an alternative material for photovoltaic and optoelectronic devices. In particular, the band gap of the 4H phase is just the right size to absorb visible light, and the 6H phase should be a potential candidate to absorb light in the ultraviolet region.