Theoretical phase diagram of ultrathin films of incipient ferroelectrics

TL;DR

This study uses first-principles calculations to map the phase diagram of ultrathin KTaO3 films, revealing surface effects induce ferroelectricity contrary to bulk behavior, aligning their phase diagrams with normal ferroelectrics.

Contribution

It provides the first theoretical phase diagram for ultrathin incipient ferroelectric films, highlighting the impact of surface/interface effects on ferroelectric behavior.

Findings

Ultrathin KTaO3 films exhibit ferroelectricity due to surface/interface effects.

The phase diagram resembles that of normal ferroelectrics like BaTiO3.

Bulk KTaO3 remains quantum paraelectric, unlike the thin films.

Abstract

We have used a first-principles-based scheme to compute the temperature-versus-misfit strain ``Pertsev'' phase diagram of ultrathin films of {\sl incipient} ferroelectric KTaO$_3$. Our results suggest that, at variance with the bulk material, KTaO$_3$ ultrathin films cannot be described as quantum paraelectrics. Rather, the behavior of the films is largely determined by surface/interface effects that favor ferroelectricity and the imperfect screening of the depolarizing fields. This leads to Pertsev phase diagrams that are qualitatively similar to those of {\sl normal} ferroelectrics such as BaTiO$_3$.