Chemical control of polymorphism and ferroelectricity in PbTiO3 and SrTiO3 monolayers and bilayers

TL;DR

This study uses density-functional theory to demonstrate how chemical bond processes in 2D PbTiO3 and SrTiO3 bilayers control ferroelectricity, enabling low-energy polarization switching influenced by strain and environment.

Contribution

It reveals how bond breakage and formation act as binary switches for ferroelectricity in 2D perovskite bilayers, introducing a new understanding of polarization control mechanisms.

Findings

Bond processes serve as binary switches for ferroelectricity.

Strain and relaxation modulate stacking-dependent ferroelectric states.

Multiple angular variables influence polarization switching.

Abstract

Layers of perovskites, found in 3D materials, 2D heterostructures, and nanotubes, often distort from high symmetry to facilitate dipole polarisation that is exploitable in many applications. Using density-functional theory calculations, ferroelectricity in bilayers of the 2D materials PbTiO3 and SrTiO3 is shown to be controlled by bond breakage and formation processes that act as binary switches. These stacking-dependent processes turn on and off as a function of relaxation from high-symmetry structures and the application of biaxial strain, and their concerted rearrangements lead to low energy barriers for ferroelectric polarisation switching. Structures with symmetry intermediate between high-symmetry octahedral forms and low-symmetry ferroelectric forms are identified, allowing the intrinsic processes associated with traditional "ferrodistortive" and "antiferrodistortive" distortions of TiO6 octahedra to be identified. Ferrodistortive-mode activity is shown to be generated by the simultaneous application of two different types of curvilinear antiferrodistortive motions. In this way, four angular variabes control polarisation switching through the concerted making and breaking of chemical bonds. These subltities make the polarisation sensitive to chemical-environment and temperature effects that manipulate strain and structure, features exploitable in futuristic devices.