Nearly Barrierless Polarization Switching Mechanisms in ZrO₂ Having Perpendicular In-Plane Domain Walls

The polarization switching mechanism in ferroelectric ZrO₂ involves the nucleation and subsequent migration of nonpolar domain boundaries; however, the fundamental mechanism driving this process remains inadequately understood. The present study introduces a mechanism for nearly barrierless polarization switching in 180° domain walls, facilitated by a the half-unit-cell nonpolar phase between oppositely polarized domains. Based on density functional theory (DFT) calculations, two types of 180° domain walls are explored, featuring head-to-head and tail-to-tail polarization boundaries, with nonpolar orthorhombic Pbcm and tetragonal P4₂/nmc phases as the respective domain walls. The calculations reveal exceptionally low energy barriers of 17.5 and 10.1 meV for migrating these Pbcm and P4₂/nmc boundaries by half a unit cell through the domains. An evaluation of the impact of defects on domain wall motion is achieved by introducing 2% oxygen vacancies or 3% Si doping, which induces a significant increase in the barrier motion activation energy, suggesting that defects serve as barriers to polarization switching.