Bidirectional mechanical switching window in ferroelectric thin films predicted by first-principle-based simulations

Abstract

Mechanical control of ferroelectric domain evolution has attracted much interest over the past decade. Nevertheless, bidirectional 180° mechanical switching, i.e., a complete cycle of mechanical writing and then erasing of a ferroelectric nanodomain, has not yet been realized in tip-film architectures. Here, via first-principles-based molecular dynamics simulations, we demonstrate that bidirectional 180° mechanical switching is possible in tip-film architectures when screening condition of ferroelectric films and tip loading force are within an appropriate window. The switching utilizes a delicate competition between the flexoelectric field and an overlooked effective dipolar field. The effective dipolar field dominates at small tip force and trigger switching from a downward single-domain state to an upward poly-domain state, whereas the flexoelectric field dominates at relatively large tip force and enables a back-switching. Bidirectional mechanical switching is achieved by applying tip force pulses with alternatively varying strength. The dipole-dipole interaction dynamics play important roles in mechanical switching.