Ferroelectric switching pathways and domain structure of SrBi2(Ta,Nb)2O9 from first principles

The energy barrier for polarization reversal is a key property that impacts the performance of ferroelectric materials. Here, the authors combine symmetry analysis and first-principles calculations to understand the origin of low-energy polarization switching in the Aurivillius-phase ferroelectrics SrBi${}₂$Ta${}₂$O${}₉$ and SrBi${}₂$Nb${}₂$O${}₉$. They show that polarization reverses via a low-energy two-step process facilitated by nonpolar structural order parameter rotations. Analysis of the ferroelectric domain structure shows that the formation of domain wall vortices is energetically favorable.