Search

The Dion-Jacobson (DJ) family of perovskite-related materials have recently attracted interest due to their polar structures and properties, resulting from hybrid-improper mechanisms for ferroelectricity in n = 2 systems and from proper mechanisms in n = 3 CsBi 2 Ti 2 NbO 10 . We report here a combined experimental and computational study on analogous n = 3 Cs Ln 2 Ti 2 NbO 10 ( Ln = La, Nd) materials. Density functional theory calculations reveal the shallow energy landscape in these systems and give an understanding of the competing structural models suggested by neutron and electron diffraction studies. The structural disorder resulting from the shallow energy landscape breaks inversion symmetry at a local level, consistent with the observed second-harmonic generation. This study reveals the potential to tune between proper and hybrid-improper mechanisms by composition in the DJ family. The disorder and shallow energy landscape have implications for designing functional materials with properties reliant on competing low-energy phases such as relaxors and antiferroelectrics., Competing Interests: The authors declare no competing financial interest.

Herein we highlight the ability to tune the structural chemistry of A-site deficient perovskite materials Ln1/3NbO3. Computational studies explore the balance between proper and hybrid-improper mechanisms for polar behaviour in these systems.

We review the theoretical, computational, and synthetic literature on hybrid improper ferroelectricity in layered perovskite oxides. Different ferroelectric mechanisms are described and compared, and their elucidation using theory and first-principles calculations is discussed. We also highlight the connections between crystal chemistry and the physical mechanisms of ferroelectricity. The experimental literature on hybrid improper ferroelectrics is surveyed, with a particular emphasis on cation-ordered double perovskites, Ruddlesden–Popper and Dion–Jacobson phases. We discuss preparative routes for synthesizing hybrid improper ferroelectrics in all three families and the conditions under which different phases can be stabilized. Finally, we survey some synthetic opportunities for expanding the family of hybrid improper ferroelectrics. [ABSTRACT FROM AUTHOR]