Finite-size effects on ferroelectricity in rhombohedral HfO2

In this work we analyze the finite-size effects on the structural properties and on the polarization of th e 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: (i) the coupling between compressive strain and the phase-transition order parameter; (ii) 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 symmetryanalysis point of view, considering the changes in the amplitude of the symmetry-allowed distortions, when a slab configuration is considered. These results are in dependent of the slabthickness 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.

Automated summary

In this research, the finite-size effects on the structural properties and polarization of rhombohedral phase of HfO2 under biaxial compressive strain are analyzed. The presence of surface charges is shown to greatly reduce the polarization compared to its bulk value, attributed to coupling between compressive strain and phase-transition order parameter, as well as changes in ferroelectric distortion. Additionally, two alternative explanations for this phenomenon are presented.