Direct determination of structural heterogeneity in metallic glasses using four-dimensional scanning transmission electron microscopy

•A new STEM technique that can determine the structural heterogeneity in disordered materials is demonstrated.•Structural heterogeneity is determined by analyzing the intensity variation of the electron nanodiffraction patterns acquired using a pixelated STEM detector.•It provides precise details of the heterogeneity, such as the type, size, distribution, and volume fraction of medium range atomic ordering, which are related to the important properties of disordered materials. We report the first direct quantification of the structural heterogeneity in metallic glasses using intensity variance and angular correlation analyses of the 4-dimensional (4-D) scanning transmission electron microscopy (STEM) data. We demonstrate that the real-space reconstruction and analyses of the 4-D nanodiffraction data acquired using a pixelated fast STEM detector enables quantitative determination of the details of local structural heterogeneity, including the type, size, volume fraction and spatial distribution of local ordering at the nano- to meso-scale, beyond the limits of the previous measurements using conventional detectors. We show that different types of local ordering are present in Zr55Co25Al20 glass, leading to a high degree of structural heterogeneity, with the total volume of locally ordered regions making up to ∼14% of the entire volume. These findings are significant, as the structure-property relationship in metallic glasses and other amorphous materials has been difficult to establish because of the lack of detailed structural information from experiments.