Transitional Structures with Continuous Variations in Atomic Positions from Anatase to Rutile Improve Photocatalytic Activity

TiO2 polymorphs have distinct properties that are widely employed in various applications. However, mechanisms of transformations between these polymorphs are not fully understood, especially at atomic scale, inhibiting advancing the design and application of the transitional phases. Here, based on results from semi-in situ transmission electron microscopy, density functional theory, and X-ray photoemission experiments, a physical picture of transitional structures is discovered, in which continuous variations in atomic positions form along a previously unreported anatase-to-rutile phase transformation path of [010](A)-to-[1 over bar 1 over bar 1$\overline 1 \overline 1 1$](R) and (004)(A)-to- (011)(R). These gradient structures give rise to continuous band bending, which promotes electron-hole separation and inhibits their recombination across the bulk of the particles, leading to a large functionally active volume fraction and resulting in high photoactivity. These findings suggest that interphase matter based on extended gradient structures can be designed to advance new functions not achievable using abrupt interfaces.