Mechanisms for collective inversion-symmetry breaking in dabconium perovskite ferroelectrics

TL;DR

This paper investigates the microscopic mechanisms behind ferroelectricity in dabconium hybrid perovskites, combining theory, simulations, and calculations to explain their polarisation and guide design of new ferroelectric materials.

Contribution

It introduces a comprehensive approach using theory, Monte Carlo simulations, and DFT to identify key factors driving ferroelectricity in dabconium perovskites, providing design rules for new ferroelectric materials.

Findings

A-site polarity and orientation along $11$ directions are crucial.

Ferroelastic strain coupling drives the ferroelectric transition.

Explains why many hybrid perovskites lack polarisation.

Abstract

Dabconium hybrid perovskites include a number of recently-discovered ferroelectric phases with large spontaneous polarisations. The origin of ferroelectric response has been rationalised in general terms in the context of hydrogen bonding, covalency, and strain coupling. Here we use a combination of simple theory, Monte Carlo simulations, and density functional theory calculations to assess the ability of these microscopic ingredients---together with the always-present through-space dipolar coupling---to account for the emergence of polarisation in these particular systems whilst not in other hybrid perovskites. Our key result is that the combination of A-site polarity, preferred orientation along $\langle111\rangle$ directions, and ferroelastic strain coupling drives precisely the ferroelectric transition observed experimentally. We rationalise the absence of polarisation in many hybrid perovskites, and arrive at a set of design rules for generating FE examples beyond the dabconium family alone.