Oxygen-vacancy-enabled charge separation in distorted orthorhombic YFeO3

Abstract

Nanoporous orthorhombic YFeO₃ was synthesized via a citrate–ethylene glycol sol–gel auto-combustion route to elucidate how oxygen-vacancy-enabled electronic states, in conjunction with lattice distortion, govern intrinsic visible-light charge separation. Rietveld refinement confirms a phase-pure Pnma lattice with pronounced FeO₆ tilting (〈ϕ〉 ≈ 18.8 ± 0.3°) and reduced Fe–O–Fe angles, which collectively lower the oxygen-vacancy formation energy and stabilize mixed-valence Fe³⁺/Fe²⁺ centers, as supported by XPS. These defect-mediated electronic modifications, together with hierarchical mesoporosity (∼54 ± 2 nm), enhance visible-light absorption, strengthen distortion-induced internal electric fields, and facilitate directional carrier transport, thereby suppressing electron–hole recombination. Optical and photoelectrochemical analyses reveal a direct band gap of 2.34 ± 0.02 eV, n-type conductivity, an enhanced photocurrent response, and an extended carrier lifetime of 3.84 ± 0.15 ns, demonstrating that oxygen vacancies and lattice distortion act cooperatively to promote long-range charge separation. This mechanistic framework was further examined using methylene blue and levofloxacin as representative probe molecules, supporting reduced activation barriers and predominantly electron-mediated (e⁻, ˙O⁻₂) reactive oxygen species pathways. The material retained its structural and electronic integrity upon repeated operation. Overall, this work establishes a unified structure–defect–function relationship for orthorhombic YFeO₃, identifying oxygen-vacancy-enabled charge separation in a distorted lattice as a key contributor to its intrinsic visible-light functionality and providing generalizable mechanistic insights for the design of defect-engineered perovskite oxides.