Pathways Towards Ferroelectricity in Hafnia

TL;DR

This paper uses first-principles calculations and group theory to identify and explain ferroelectric phases in hafnia, revealing new pathways to stabilize ferroelectricity in this material.

Contribution

It systematically identifies potential ferroelectric phases of hafnia using structure search algorithms and symmetry analysis, explaining recent experimental observations.

Findings

Identified two orthorhombic polar phases with low free energy

These phases exhibit substantial switchable polarization

Results explain observed ferroelectric behavior in hafnia

Abstract

The question of whether one can systematically identify (previously unknown) ferroelectric phases of a given material is addressed, taking hafnia (HfO$_2$) as an example. Low free energy phases at various pressures and temperatures are identified using a first-principles based structure search algorithm. Ferroelectric phases are then recognized by exploiting group theoretical principles for the symmetry-allowed displacive transitions between non-polar and polar phases. Two orthorhombic polar phases occurring in space groups $Pca2_1$ and $Pmn2_1$ are singled out as the most viable ferroelectric phases of hafnia, as they display low free energies (relative to known non-polar phases), and substantial switchable spontaneous electric polarization. These results provide an explanation for the recently observed surprising ferroelectric behavior of hafnia, and reveal pathways for stabilizing ferroelectric phases of hafnia as well as other compounds.