Extrinsic nature of the polarization in hafnia ferroelectrics

TL;DR

This paper demonstrates through first-principles simulations that the polarization in hafnia ferroelectrics is extrinsic, depending on environmental factors, challenging traditional views on ferroelectricity in these materials.

Contribution

It reveals that the polarization sign in hafnia is environment-dependent and extrinsic, providing new insights into ferroelectric behavior in hafnia and related materials.

Findings

Polarization sign depends on environment

Depolarizing fields can be positive or negative

Polarization is extrinsic in hafnia

Abstract

Hafnia and related fluorites defy our understanding of ferroelectricity, even if we restrict ourselves to the intrinsic properties of ideal crystals. Here we focus on a critical puzzle, namely, the sign of the electric polarization. Using first-principles simulations, we show that a polar hafnia layer with a fixed atomic configuration can give rise to depolarizing fields of either positive or negative sign, depending on the environment. This implies that (the sign of) the polarization in hafnia is extrinsic in nature. We explain this result and discuss its relevance to other ferroelectric families.