Domains and ferroelectric switching pathways in Ca$_3$Ti$_2$O$_7$ from first principles

TL;DR

This study uses first-principles calculations and group theory to identify multiple ferroelectric switching pathways in Ca$_3$Ti$_2$O$_7$, revealing complex mechanisms involving domain walls and structural distortions.

Contribution

It introduces a comprehensive analysis of ferroelectric switching pathways in Ca$_3$Ti$_2$O$_7$ using first-principles and group theoretic methods, highlighting multiple mechanisms.

Findings

Multiple low-energy switching paths identified

Switching can occur via orthorhombic twin domains

Switching may involve antipolar structures

Abstract

Hybrid improper ferroelectricity, where an electrical polarization can be induced via a trilinear coupling to two non-polar structural distortions of different symmetry, has recently been experimentally demonstrated for the first time in the $n$=2 Ruddlesden-Popper compound Ca$_3$Ti$_2$O$_7$. In this paper we use group theoretic methods and first-principles calculations to identify possible ferroelectric switching pathways in Ca$_3$Ti$_2$O$_7$. We identify low-energy paths that reverse the polarization direction by switching via an orthorhombic twin domain, or via an antipolar structure. We also introduce a chemically intuitive set of local order parameters to give insight into how these paths are relevant to switching nucleated at domain walls. Our findings suggest that switching may proceed via more than one mechanism in this material.