First-principles investigation of incipient ferroelectric trends of rutile TiO$_2$ in bulk and at the (110) surface

TL;DR

This study uses first-principles density functional theory to explore the incipient ferroelectric behavior of rutile TiO$_2$ in bulk and at the (110) surface, revealing mechanisms and conditions for stabilizing ferroelectric phases.

Contribution

It provides a detailed analysis of the ferroelectric tendencies of rutile TiO$_2$ and shows how lattice distortions and surface strain influence ferroelectric phase stabilization.

Findings

Ferroelectric phases can be stabilized by lattice distortions that increase the shortest Ti-O distance.

Surface ferroelectric trends are modified but large polarization can still be achieved with uniaxial strain.

A ferroelectric phase can be stabilized even at the topmost surface layer of rutile TiO$_2$.

Abstract

The ferroelectric trends of rutile (TiO$_2$) in bulk and at the (110) surface are investigated by means of ab initio density functional theory. We discuss the underlying mechanism of the incipient ferroelectric behavior of rutile in terms of Born effective charges, which we decompose in individual contributions by means of maximally localized Wannier functions. We show that a ferroelectric phase can be stabilized for a variety of different lattice distortions which all enlarge the shortest Ti-O distance, even if the longer apical Ti-O bond is simultaneously shortened. At the (110) surface, the ferroelectric trends are modified compared to the bulk, but nevertheless ferroelectric phases with large polarization even in the topmost surface layer can be stabilized by uniaxial strain.