Alternating atomic-dipole layers and switching dynamics in Al_1-xSc_xN ferroelectrics

Wurtzite Al_1-xSc_xN ferroelectrics exhibit exceptional polarization and thermal stability, making them highly promising for a wide range of electronic applications. However, a more profound understanding is required regarding the atomic-scale mechanism through which cation substitution lowers the switching energy barrier and thus reduces the coercive field. We used spherical aberration-corrected transmission electron microscopy to reveal a periodic modulation of cation-anion spacing along the polarization direction, forming alternating atomic dipole layers. This modulation arises from energetically favorable chemical ordering of aluminum and scandium atoms between adjacent layers, with layer-resolved asymmetry in atomic arrangement. In situ imaging directly captures atomic-scale, noncollective, stepwise polarization switching, revealing intermediate states and local spacing fluctuations. Compositional inhomogeneity in these dipole layers creates multiple transient states that reduce the switching energy barrier. Our findings connect atomic-scale dipole structures to polarization switching kinetics, enabling the rational design of wurtzite ferroelectrics.