In-Situ Observation of Atom Motion and Manipulation of Structural Transformation.

Abstract

Precisely controlling structural transformations is essential for realizing novel functionalities in crystal materials, as these transformations often result in significant changes in physical and chemical properties. However, such structural control at the atomic scale remains a formidable challenge. Here the direct observation and realization of atomic scale structural transformation is demonstrated from KTaO₃ to K₆Ta_10.8O₃₀ via high-energy electron beam manufacturing in scanning transmission electron microscope (STEM), which can finally manipulate the Ta atom movements. The K and O vacancies in KTaO₃ can be introduced via the knock-on energy transferred from the controled high-dose electron beams. These vacancies can further accommodate Ta atom emerging at the interstitial sites of the TaO₂ plane in KTaO₃. Thus, all atom species in KTaO₃ can be stimulated via electron beam and the cooperative movements of them trigger the final formation of the new K₆Ta_10.8O₃₀ phase. The detailed mechanisms are revealed by low-dose, in situ, atomic scale imaging under STEM. The controllability of this electron beam manufacture process and the stability of the new K₆Ta_10.8O₃₀ phase is further validated. DFT calculations rationalize the triggering steps of the manufacture process and show the transformation is energetically beneficial at the condition of K and O vacancies introduced by knock-on effect. This work not only investigates the microscopic mechanism of electron beam-induced structural transformation, but also establishes a versatile pathway for synthesizing new functional materials with tailored properties.