Kinetically-stabilized Ferroelectricity in Bulk Singlecrystalline HfO2:Y without Wake-up Effects

TL;DR

This study demonstrates that bulk single-crystalline HfO2:Y exhibits stable ferroelectricity without wake-up effects, achieved through advanced synthesis and characterization, challenging previous notions that ferroelectricity in HfO2 is limited to thin films.

Contribution

The paper reports the first observation of ferroelectricity in bulk single-crystalline HfO2:Y, revealing phase control via rapid cooling and doping, and providing new insights into its polymorphic nature.

Findings

Ferroelectricity observed in bulk HfO2:Y crystals.

Presence of anti-polar Pbca phase at different Y concentrations.

Switchable polarization with minimal wake-up effects.

Abstract

HfO2, a simple binary oxide, holds ultra-scalable ferroelectricity integrable into silicon technology. Polar orthorhombic (Pbc21) form in ultra-thin-films ascribes as the plausible root-cause of the astonishing ferroelectricity, which has thought not attainable in bulk crystals. Though, perplexities remain primarily due to the polymorphic nature and the characterization challenges at small-length scales. Herein, utilizing a state-of-the-art Laser-Diode-heated Floating Zone technique, we report ferroelectricity in bulk single-crystalline HfO2:Y as well as the presence of anti-polar Pbca phase at different Y concentrations. Neutron diffraction and atomic imaging demonstrate (anti-)polar crystallographic signatures and abundant 90o/180o ferroelectric domains in addition to the switchable polarization with little wake-up effects. Density-functional theory calculations suggest that the Yttrium doping and rapid cooling are the key factors for the desired phase. Our observations provide new insights into the polymorphic nature and phase controlling of HfO2, remove the upper size limit for ferroelectricity, and also pave a new road toward the next-generation ferroelectric devices.