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

[摘要] Several families of layered perovskite oxide ferroelectrics exhibit a coupling between polarization and structural order parameters, such as octahedral rotation distortions. This coupling provides opportunities for novel electric field-based manipulation of material properties, and it also stabilizes complex domain patterns and domain-wall vortices. Among layered perovskites with such coupled orders, the Aurivillius-phase oxides SrBi2B2O9 (B = Ta, Nb) are well-known for their excellent room-temperature ferroelectric performance. This work combines group theoretic analysis with density functional theory calculations to examine the ferroelectric switching processes of SrBi2B2O9. Low-energy two-step ferroelectric switching paths are identified, with polar-ization reversal facilitated by structural order-parameter rotations. Analysis of the domain structure reveals how the relative energetics of the coupled order parameters translates into a network of several distinct domain-wall types linked by domain-wall vortex structures. Comparisons are made between the ferroelectric switching and domain structure of SrBi2B2O9 and those of the layered n = 2 Ruddlesden-Popper hybrid improper ferro-electrics. The results provide insight into how ferroelectric properties may be optimized by engineering the complex crystal structures of Aurivillius-phase oxides.

[关键词] IMPROPER FERROELECTRICITY;PHASE-TRANSITIONS;CRYSTAL-STRUCTURE;CAPACITORS;ORIGIN;WALLS