Collective behavior in intrinsic polarization switching of PbTiO3 and Pb(Zr,Ti)O3

Ferroelectric materials play a pivotal role in various industrial and scientific applications due to their ability to exhibit spontaneous electric polarization above a critical temperature. The application of a sufficiently high external electric field can induce the switching of the spontaneous polarization, with the specific mechanism varying across different materials. Understanding the intrinsic switching mechanism is paramount for regulating polarization domains, thereby unlocking potential applications in nanoelectronic devices. Different types of switching mechanisms have been experimentally reported and various models have been developed, among them the nucleation-limited-switching (NLS) model, which is distinguished by nucleation and limited propagation. We investigate the intrinsic polarization switching mechanisms in PbTiO3 and Pb(Zr,Ti)O3 using molecular dynamics simulations. We found that both PbTiO3 and Pb(Zr,Ti)O3 exhibit the change of switching mechanisms as the field increases. At high electric field, they both follow homogeneous switching mechanism without the nucleation of domains. At weak electric fields, the NLS model effectively described the switching behavior of both PbTiO3 and Pb(Zr,Ti)O3, although the atomistic details of their respective switching mechanisms diverge. We demonstrate that, for PbTiO3, the switching mechanism at weak fields involves the collective behavior near nuclei such as the formation of vortices, which is characterized by the hypertoroidal moment. We also report the substantial in-plane dipolar pattern of Pb(Zr,Ti)O3 at low fields, independent of switching. This work contributes to a comprehensive understanding of ferroelectric switching and, thus, results in better prediction of designing new nanoelectronic devices.