Dynamic Structure Evolution under Invariant Lattice Framework in Fluorite-Type Ferroelectrics

Insightful design of HfO2-based ferroelectric (FE) devices for encoding and storage necessitates a comprehensive understanding of the dynamics governing structure evolution. However, conclusive experimental evidence remains limited. Here, by in situ biasing directly on the TiN/Hf0.5Zr0.5O2/TiN FE capacitors and combining theoretical calculations, we reveal the atomic-scale domain structure evolution via a transient polar orthorhombic (O)-Pmn21-like configuration. Direct atomic evidence demonstrates that the antipolar O-Pbca phase could transform into the FE O-Pbc21 phase under electric fields, and the polar axis of the FE phase aligns toward the bias direction through a ferroelastic transformation, thereby enhancing FE polarization. As the bias increases, the polar axis collapses, leading to FE degradation. Throughout the process of domain structure evolution, the lattice framework retains its integrity without alteration. These insights into the intricate structure evolution under electrical field cycling facilitate optimization and design strategies for HfO2-based FE memory devices.