Origin of Interstitial Doping Induced Coercive Field Reduction in Ferroelectric Hafnia

Hafnia-based ferroelectrics hold promise for nonvolatile ferroelectric memory devices. However, the high coercive field required for polarization switching remains a prime obstacle to their practical applications. A notable reduction in coercive field has been achieved in ferroelectric Hf(Zr)_{1+x}O_{2} films with interstitial Hf(Zr) dopants [Science 381, 558 (2023)SCIEAS0036-807510.1126/science.adf6137], suggesting a less-explored strategy for coercive field optimization. Supported by density functional theory calculations, we demonstrate the Pca2_{1} phase, with a moderate concentration of interstitial Hf dopants, serves as a minimal model to explain the experimental observations, rather than the originally assumed rhombohedral phase. Large-scale deep potential molecular dynamics simulations suggest that interstitial defects promote the polarization reversal by facilitating Pbcn-like mobile 180° domain walls. A simple prepoling treatment could reduce the switching field to less than 1  MV/cm and enable switching on a subnanosecond timescale. High-throughput calculations reveal a negative correlation between the switching barrier and dopant size and identify a few promising interstitial dopants for coercive field reduction.