  Ferroelectrics and ionic conductors are important functional materials, each
supporting a plethora of applications in information and energy technology. The
underlying physics governing their functional properties is ionic motion, and
yet studies of ferroelectrics and ionic conductors are often considered
separate fields. Based on first-principles calculations and
deep-learning-assisted large-scale molecular dynamics (MD) simulations, we
report ferroelectric-switching-promoted oxygen ion transport in HfO$_2$, a
wide-band-gap insulator with both ferroelectricity and ionic conductivity.
Applying a unidirectional bias can activate multiple switching pathways in
ferroelectric HfO$_2$, leading to polar-antipolar phase cycling that appears to
contradict classical electrodynamics. This apparent conflict is resolved by the
geometric-quantum-phase nature of electric polarization that carries no
definite direction. Our MD simulations demonstrate bias-driven successive
ferroelectric transitions facilitate ultrahigh oxygen ion mobility at moderate
temperatures, highlighting the potential of combining ferroelectricity and
ionic conductivity for the development of advanced materials and technologies.
