Phase transitions of materials are usually accompanied by a remarkable change of properties. Tracing and identifying the structural changes at the atomic scale is the key to understanding the fundamental mechanisms behind their performances. However, the direct observation of three-dimensional structural transformations in single nanocrystals has been rarely achieved. Herein we reported the development of an in situ three-dimensional electron diffraction (3D ED) approach for single nanocrystal structural analysis by combining 3D ED with in situ transmission electron microscopy. Each data set covering a crystal tilting range of 50° was collected in around 1 min at the set temperature using an in situ heating holder. The feasibility of this protocol was proved by its successful application in investigating the metal–insulator transition (MIT) of vanadium dioxide (VO2) crystals with atomic precision. Moreover, local domains were found in the monoclinic phase before and after the annealing process, of which the orientations obey a 4-fold rotation symmetry along the a-axis.
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