Tuning between Proper and Hybrid-Improper Mechanisms for Polar Behavior in CsLn 2Ti2NbO10 Dion-Jacobson Phases.

Vanessa A Cascos,Martin C Stennett,Igor Levin,Emma E Mccabe,Neil C Hyatt,Weiguo Zhang,Jennifer Roberts-Watts,Eric Bousquet,Chloe Skingle,P Shiv Halasyamani

doi:10.1021/acs.chemmater.0c03326

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 CsBi2Ti2NbO10. We report here a combined experimental and computational study on analogous n = 3 CsLn2Ti2NbO10 (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.

Highlights

Ferroelectrics are widely used in applications such as sonars and sensors,[1] electrooptics,[2] capacitors,[3] and memory devices,[4] making them materials of significant technological importance
Hybrid-improper mechanisms for ferroelectricity rely on coupling nonpolar distortions to break inversion symmetry and stabilize polar displacements.[9,10]
Preliminary characterization was carried out using X-ray powder diffraction (XRPD) using a Bruker D8 Advance diffractometer operating in reflection mode with a Cu Kα source and a Vantec detector

Summary

Introduction

Ferroelectrics are widely used in applications such as sonars and sensors,[1] electrooptics,[2] capacitors,[3] and memory devices,[4] making them materials of significant technological importance. Hybrid-improper mechanisms for ferroelectricity rely on coupling nonpolar distortions (such as rotations of octahedra in layered perovskite-related materials) to break inversion symmetry and stabilize polar displacements.[9,10] This opens up the possibility of preparing new families of polar materials. These two mechanisms give distinctly different temperature-dependence of polar characteristics such as permittivity and the possibility to tune the temperature scale and range of functional properties

Methods

Results

Discussion

Conclusion