Short-Range Fringing Field-Driven Charge Separation in Mixed-Phase TiO₂ Nanoparticles

Combining near-coincidence-site lattice (NCSL) calculations and fringing-field simulations, we investigate the formation conditions and spatial vector distribution of the interfacial electric field at anatase/rutile phase junctions in TiO₂ nanoparticles. Our analysis reveals that charge separation in these mixed-phase systems is governed not by the long-range built-in field of a classical depletion region, but by a strong, short-range fringing field localized at the phase boundary. The minority-carrier migration length defines an optimal phase-size combination of approximately 20 nm anatase and 6–13 nm rutile, within which the fringing-field strength exceeds 10² kV·cm^–1. This work provides a quantitative design principle for enhancing charge separation efficiency through precise nanoscale phase engineering in mixed-phase photocatalysts and photovoltaic devices.