Understanding the appearance of commensurate and incommensurate modulations in perovskite antiferroelectrics (AFEs) is of great importance for material design and engineering. The dielectric and elastic properties of the AFE domain boundaries are lack of investigation. In this work, a novel Landau theory is proposed to understand the transformation of AFE commensurate and incommensurate phases, by considering the coupling between the oxygen octahedral tilt mode and the polar mode. The derived relationship between the modulation periodicity and temperature is in good agreement with the experimental results. Using the phase field study, we show that the polarization is suppressed at the AFE domain boundaries, contributing to a remnant polarization and local elastic stress field in AFE incommensurate phases.
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