# Tuning between proper and hybrid-improper mechanisms for polar behaviour in CsLn$$_2$$Ti$$_2$$NbO$$_{10}$$ Dion-Jacobson phases

Cascos, Vanessa A., Roberts-Watts, Jennifer, Skingle, Chloe, Levin, Igor, Zhang, Weiguo, Halasyamani, P. Shiv, Stennett, Martin C., Hyatt, Neil C., Bousquet, Eric, McCabe, Emma E. and others. (2020) Tuning between proper and hybrid-improper mechanisms for polar behaviour in CsLn$$_2$$Ti$$_2$$NbO$$_{10}$$ Dion-Jacobson phases. Chemistry of Materials, 32 (19). pp. 8700-8712. ISSN 0897-4756. (doi:10.1021/acs.chemmater.0c03326) (KAR id:83192)

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## Abstract

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 CsLn$$_2$$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.

Item Type: Article 10.1021/acs.chemmater.0c03326 Q Science Divisions > Division of Natural Sciences > Physics and Astronomy Emma McCabe 30 Sep 2020 09:00 UTC 21 Sep 2021 23:00 UTC https://kar.kent.ac.uk/id/eprint/83192 (The current URI for this page, for reference purposes) https://orcid.org/0000-0001-5868-4570