Transitional Structures of Continuous Variations in Atomic Positions Induce High Photocatalytic Efficiency

Polymorphs widely exist in nature and synthetic systems and are well known to determine material properties. Understanding phase transformation mechanisms among polymorphs enables the design of structures and tuning of phases to tailor material properties. However, current understanding is limited due to the lack of direct observations of the structural evolution at the atomic scale. Here, integrating (semi) in situ transmission electron microscopy and density functional theory, we report atomic structural evolutions of phase transformation from anatase (A) to rutile (R), brookite (B), R-phase, and TiO. Understanding the atomic structural evolution sheds light on interpreting and controlling TiO₂ polymorphs and interface structures for various applications. Here, we reveal the transitional atomic gradient structures (continuous variations in atomic positions), that form during phase transformation processes, alter electronic structures in 3D across the bulk of the crystals and thus substantially increase the active volume to separate electrons and holes and the resulting photoactivity. These new insights suggest that interphase matter based on gradient structures can be designed to induce new functions not achievable using abrupt interfaces. These findings enable a new materials design paradigm that can potentially be harnessed for a broad range of applications.