Atomic-level insights into the high intrinsic thermostability of individual anatase TiO2 nanocrystals through surface-locking effects

Abstract

Abstract Nanocrystal phase thermostability is critical for their applications, yet fundamentally governed by complex thermodynamic and kinetic variables. Understanding the stabilizing mechanisms and dominant factors requires atomic-level insights into dynamic evolution across surface and bulk regions under extreme conditions. Herein, we present a comprehensive in-situ investigation of individual single-crystalline anatase TiO 2 nanorods using spherical aberration-corrected scanning transmission electron microscopy. By simultaneously acquiring environmental secondary electron images for surface topography and high-angle annular dark-field images for bulk atomic structures, we reveal the extraordinary phase stability of individual anatase nanorods governed by surface effects, distinct from aggregated nanorods. Anatase TiO 2 nanorods undergo morphology reshaping and surface atomic reconstruction above 600 °C, involving transformation from high-index surfaces to (101) facets and the formation of (1 × 4)-reconstructed (001) surfaces. Remarkably, individual anatase TiO 2 nanorods maintain the anatase structure even up to 1250 °C without transforming into the rutile phase. The restructuring lowers the total energy of the system, and acts as a kinetic “surface-locking” effect preventing rutile nucleation. Beyond elucidating the restructuring mechanisms and intrinsic thermostability of TiO 2 nanocrystals, this work also establishes an effective pathway for simultaneously probing the complex structural evolution of nanomaterials across both surface and bulk regions.