Domain Walls Stabilized by Intrinsic Phonon Modes and Engineered Defects Enable Robust Ferroelectricity in HfO2

TL;DR

This study uncovers how intrinsic phonon modes and engineered defects stabilize domain walls in HfO2, leading to enhanced and robust ferroelectricity, supported by theoretical and experimental evidence.

Contribution

The paper introduces a unified phonon mode expansion framework combined with first-principles calculations to understand domain wall stabilization in HfO2, highlighting the role of interface phonons and defects.

Findings

Interface phonon modes are crucial for domain wall stability.

Defects pin and stabilize ferroelectric domains.

Experimental observations confirm theoretical predictions.

Abstract

Ferroelectric $\mathrm{HfO}_2$ has attracted extensive research interest for its applications in AI era. The domain walls play a crucial role in phase structure stabilization and polarization switching of ferroelectric $\mathrm{HfO}_2$, however, a thorough understanding is still lacking. Here, we developed a unified framework based on phonon mode expansion to systematically study the effects of phonon modes and defects on domain wall structures. Using this approach combined with first-principle calculations, we revealed that the interface phonon modes play a key role in stability of domain walls; defects pin and stabilize ferroelectric domains, which in turn stabilizes the metastable orthorhombic phase and facilitates polarization switching. This provides an insight from the microscopic physics origin into the enhanced ferroelectricity in $\mathrm{HfO}_2$ by doping and defect engineering. Furthermore, the theoretically predicted domain structures and defect distributions were observed in La-doped $\mathrm{HfO}_2$ ferroelectric films by EELS and STEM experiments, which confirms the validity of our findings.