Pressure-driven semiconductor-semiconductor transition and its structural origin in oxygen vacancy ordered SrCo O2.5

SrCoO2.5 has a long-range oxygen vacancy ordering that makes it a promising energy material and catalyst carrier. The study of its electronic properties is vital for its practical applications. Here, we investigate its electronic behavior and lattice structural evolution under high pressure up to 22 GPa using synchrotron infrared spectroscopy and x-ray diffraction. A clear electronic transition from a semiconducting state to another semiconducting state is observed around 7.3 GPa upon compression, based on infrared results. Detailed structural examination shows that this electronic transition is accompanied by a structural phase transition, which occurs between 5.3 and 8.6 GPa, as confirmed by x-ray diffraction. The band gap reduces by ∼40% at high pressure compared to ambient conditions. This work demonstrates that the oxygen vacancy ordering in SrCoO2.5 can be sustained up to ∼8.6GPa and pressure can narrow the band gap, forcing this unique material to enter into another electronic state with a new crystal structure.