Abstract
We use a recently developed method—based on layer group analysis combined with the Landau theory—to investigate the polar properties of antiphase boundaries (APBs) in SrTiO3 and PbZrO3. For SrTiO3, we find that, in addition to the biquadratic, Houchmandazeh-Laizerowicz-Salje (HLS) coupling bijklPiPjϕkϕl in the Landau-Ginzburg free energy expansion, additional rotopolar terms of the form WijklPiϕk∂ϕl∂xj contribute considerably to the polarization of antiphase boundaries in these materials. The rotopolar terms can be split into a symmetric flexoelectric part and an antisymmetric one. The antisymmetric Lifshitz term leads to a macroscopic polarization of APBs, which can be switched by application of an external electric field. For PbZrO3, the observed polarization profiles [Wei et al., Mater. Res. Bull. 62, 101 (2015)] are fully compatible with the symmetries of the corresponding layer groups. Unlike in SrTiO3, there exists no Lifshitz invariant WijklPiηk∂ηl∂xj for the order parameter ηi(i=1,…,12) describing the displacements of lead atoms. However, a detailed group theoretical treatment indicates that the polarity of APBs in PbZrO3 is driven by higher order interactions between polarization Pi, order parameter ηk, and order parameter gradients ∂ηl∂xj.
Highlights
Domain walls (DWs) have attracted much interest due to their ability of carrying functional properties1–5 that are different from the surrounding bulk
We show qualitatively how these couplings contribute to the polarization components of the present antiphase boundaries (APBs) and how the polarization profiles correlate with the layer group symmetry of the twin
We have analyzed the polar properties of translational antiphase boundaries (APBs) of SrTiO3 (STO) and PbZrO3 (PZO)
Summary
Domain walls (DWs) have attracted much interest due to their ability of carrying functional properties that are different from the surrounding bulk. It turned out that this rotopolar coupling allows for a breakdown of macroscopic inversion symmetry—similar to in cycloidal magnets—which leads to a macroscopic polarization of a special sequence of parallel ferroelastic DWs. Very recently, we have studied the polarization of domain boundaries in SrTiO3 using a combination of layer groups with order parameter (OP) symmetry. We found that the special sequence of ferroelastic DWs produces a net macroscopic polarization that must always contain a mixed ferroelastic DW, i.e., of the orientational/translational type that contains an antiphase boundary (APB). In this way, we unveiled that the rotopolar coupling provides an important mechanism for polarization of translational APBs. scitation.org/journal/jap polarization.. The rotopolar coupling between polarization and gradients of the primary order parameter, which was identified to lead to a macroscopic polarization from antiferrodistortive cycloids in SrTiO3, is shown here to contribute significantly to DW polarization in APBs of SrTiO3 and PbZrO3
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