In this work we analyze the finite-size effects on the structural properties and on the polarization of the rhombohedral phase of HfO2 subjected to a biaxial compressive strain. We show how the presence of surface charges affects the polarization, leading to a strong reduction with respect to its bulk value. This reduction can be ascribed to two mechanisms: the coupling between compressive strain and the phase-transition order parameter; the changes in the ferroelectric distortion. We give two alternative explanations of this phenomenon: from an atomistic point of view, analyzing the evolution of the bond lengths, and from a symmetry-analysis point of view, considering the changes in the amplitude of the symmetry-allowed distortions, when a slab configuration is considered. These results are independent on the slab-thickness in the considered range, suggesting the absence of a critical thickness for ferroelectricity in HfO2, in agreement with the proposed improper nature of hafnia ferroelectricity.
@article{arxiv.2204.05252,
title = {Finite-size effects on the ferroelectricity in rhombohedral HfO$_2$},
author = {Francesco Delodovici and Paolo Barone and Silvia Picozzi},
journal= {arXiv preprint arXiv:2204.05252},
year = {2022}
}