Ferroelectricity in $\mathrm{Hf}{\mathrm{O}}_2$ from a chemical perspective

Abstract

Ferroelectricity observed in thin film $\mathrm{Hf}{\mathrm{O}}_2$, either doped with Si, Al, etc. or in the $\mathrm{H}{\mathrm{f}}_{0.5}\mathrm{Z}{\mathrm{r}}_{0.5}{\mathrm{O}}_2$ form, has gained great technical significance. However, the soft mode theory faces a difficulty in explaining the origin of such ferroelectricity. In this work, we propose that the 7 cation coordination number of $\mathrm{Hf}{\mathrm{O}}_2/Zr{\mathrm{O}}_2$ lies at the heart of this ferroelectricity, which stems from the proper ionic radii of Hf/Zr compared with O. Among the numerous compounds with non-centrosymmetric nature, e.g., $mm2$ point group, $\mathrm{Hf}{\mathrm{O}}_2$ and $\mathrm{Zr}{\mathrm{O}}_2$ are special in that they are close to the border of 7 and 8 cation coordination, such that the 8-coordination tetragonal intermediate phase could greatly reduce the switching barrier. Other 7-coordination candidates, including $\mathrm{Sr}{\mathrm{I}}_2$, TaON, YSBr and YOF are also studied in comparison to $\mathrm{Hf}{\mathrm{O}}_2$/$\mathrm{Zr}{\mathrm{O}}_2$, and six switching paths are analyzed in detail for the $Pca{2}_1$ phase. A rule of preferred switching path in terms of ionic radii ratio and coordination number has been established. We also show the possible route from ferroelectric $Pca{2}_1$ phase to monoclinic $P{2}_1/c$ phase in $\mathrm{Hf}{\mathrm{O}}_2$, which is relevant to the fatigue phenomenon.

14 pages, 4 figures

References in corpus (5)

• The Origin of Ferroelectricity in Hf${}_x$ Zr${}_{1-x}$ O${}_2$: A Computational Investigation and a Surface Energy Model
• Pathways Towards Ferroelectricity in Hafnia
• Intrinsic ferroelectricity in Y-doped HfO2 thin films
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• Antiferroelectric negative capacitance from a structural phase transition in zirconia

Cited by in corpus (5)

• Progress in Computational Understanding of Ferroelectric Mechanisms in HfO${}_2$
• Disentangling stress and strain effects in ferroelectric HfO2
• Flexoelectricity-stabilized ferroelectric phase with enhanced reliability in ultrathin La:HfO2 films
• Impact of Zr substitution on the electronic structure of ferroelectric hafnia
• Phase transitions in typical fluorite-type ferroelectrics