Atomic Layer Engineering of Ferroelectricity in Dion–Jacobson Perovskites

Recent advances in “hybrid-improper” ferroelectricity in Dion–Jacobson (DJ)-type layered perovskites have caused renewed interest in the search for new ferroelectrics. Here, we present an approach for the tailored synthesis of a new homologous series of DJ-type layered perovskites Cs(Bi₂Sr_n–3)(Ti_n–1Nb)O_3n+1. Starting from CsBi₂Ti₂NbO₁₀ (n = 3), higher-order homologous phases with n = 4 and 5 were successfully synthesized by repeated solid-state calcination with SrTiO₃. Characterizations by X-ray diffraction, electron diffraction, transmission electron microscopy, Raman scattering, and second harmonic generation showed the detailed structural features in Cs(Bi₂Sr_n–3)(Ti_n–1Nb)O_3n+1, and the polar structures could be stabilized by proper or hybrid-improper ferroelectricity, depending on the odd or even number of the perovskite layers. Our results provide important insights into the competition between the different mechanisms and the consequences of the ferroelectric properties in homologous layered perovskites.