New on PRB: Finite-size effects on ferroelectricity in rhombohedral HfO2

Great news from theoretical modeling of hafnia!

In this work we analyze the finite-size effects on the structural properties and on the polarization of th e rhombohedral phase of HfO<sub>2</sub> 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 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 in dependent of the slab thickness in the considered range, suggesting the absence of a critical thickness for ferroelectricity in HfO<sub>2</sub>, in agreement with the proposed improper nature of hafnia ferroelectricity.

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Francesco Delodovici, Paolo Barone, and Silvia Picozzi
Phys. Rev. B 106, 115438 – Published 29 September 2022

DOI: 10.1103/PhysRevB.106.115438