In-situ atomic visualization of structural transformation in Hf 0.5 Zr 0.5 O 2 ferroelectric thin film: from nonpolar tetragonal phase to polar orthorhombic phase

For the first time, we directly visualized the dynamic process of phase transformation in polycrystalline ferroelectric (FE) Hf 0.5 Zr 0.5 O 2 (HZO) thin film though in-situ spherical aberration (Cs)-corrected transmission electron microscopy (TEM) technique. The main observations are: (1) the dynamic atomic scale structural evolution from centrosymmetric tetragonal (t-) phase to FE orthorhombic (o-) phase under electric field, and (2) the deformation of atomic arrangements in lattice caused by stress is helpful to make the transition happen. These observations provide solid evidence on understanding the fundamental mechanism of the root cause of ferroelectricity in fluorite-type FE materials.