Point defect induced incommensurate dipole moments in the KCa2Nb3O10 Dion-Jacobson layered perovskite

Abstract

Local structural distortions due to isolated atomic defects and defect complexes strongly affect the macroscopic properties of oxide ceramics. While the characterization of local defect structures is more common in simple $\mathrm{AB}{\mathrm{O}}_{3}$ perovskites, unambiguous determination of the same in layered perovskites is more difficult due to their complex crystal structures. Here, we combined x-ray pair distribution function and density functional theory calculations to characterize the structure of cation-oxygen divacancy pairs in a Dion-Jacobson (D-J) layered perovskite. Our results indicate that local incommensurate dipole moments with polarization density in the range of $\ensuremath{\sim}0.1--17\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{C}/\mathrm{c}{\mathrm{m}}^{2}$ are created due to divacancy-induced structural distortions in the D-J phase $\mathrm{K}{\mathrm{Ca}}_{2}{\mathrm{Nb}}_{3}{\mathrm{O}}_{10}$. This is comparable with defect dipole moments observed in well-known perovskite ferroelectrics. The current results imply that controlling the atomic defects can potentially lead to significant control of dielectric properties in D-J layered perovskites.