Recipes for improper ferroelectricity in molecular perovskites

Hanna L B Boström,Mark S Senn,Andrew L Goodwin

doi:10.1038/s41467-018-04764-x

Hanna L B Boström, Mark S Senn + Show 1 more

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https://doi.org/10.1038/s41467-018-04764-x

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Journal: Nature Communications	Publication Date: Jun 18, 2018
Citations: 95	License type: open-access

Affiliation: University of Oxford, University of Warwick

Abstract

The central goal of crystal engineering is to control material function via rational design of structure. A particularly successful realisation of this paradigm is hybrid improper ferroelectricity in layered perovskite materials, where layering and cooperative octahedral tilts combine to break inversion symmetry. However, in the parent family of inorganic ABX3 perovskites, symmetry prevents hybrid coupling to polar distortions. Here, we use group-theoretical analysis to uncover a profound enhancement of the number of improper ferroelectric coupling schemes available to molecular perovskites. This enhancement arises because molecular substitution diversifies the range of distortions possible. Not only do our insights rationalise the emergence of polarisation in previously studied materials, but we identify the fundamental importance of molecular degrees of freedom that are straightforwardly controlled from a synthetic viewpoint. We envisage that the crystal design principles we develop here will enable targeted synthesis of a large family of new acentric functional materials.

Highlights

The central goal of crystal engineering is to control material function via rational design of structure
Ferroelectricity is comparatively rare in bulk perovskite materials and BaTiO3 is much more of an exception than a rule[9]
Discussion we can conclude that, from a group-theoretical viewpoint, perovskites with a molecular component are remarkably predisposed to crystallising in polar space groups. This attractive property is a result of the large number of polar coupling schemes generated by distortions accessible to molecular perovskites but inaccessible to conventional inorganic perovskites

Summary

Introduction

The central goal of crystal engineering is to control material function via rational design of structure. Ferroelectricity is comparatively rare in bulk perovskite materials and BaTiO3 is much more of an exception than a rule[9] It is in this context that the concept of hybrid improper ferroelectricity is especially appealing[10]. In favourable cases, a combination of two or more modes—each non-polar in their own right—may collectively lift inversion symmetry and give rise to a polar secondary order parameter[10,12]. This so-called hybrid improper ferroelectricity mechanism is attractive from a crystal engineering perspective because it lends itself to design rules via group-theoretical analysis[10].

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