Electrostriction-Driven Phase Instability Enables Giant Pseudo-Piezoelectricity in Hf<sub>0.5</sub>Zr<sub>0.5</sub>O<sub>2</sub>
<p dir="ltr">The electromechanical properties of hafnium zirconium oxide fluorite (Hf<sub>0.5</sub>Zr<sub>0.5</sub>O<sub>2</sub>, HZO) remain largely unexplored despite its widespread use as a ferroelectric in CMOS-compatible devices. Here, we demonstrate that electrostriction-driven phase instability enables a giant pseudo-piezoelectric response in epitaxial HZO thin films. Above a critical field of 24 kV·cm<sup>-1</sup>, field-induced transitions between nonpolar and polar phases activate an extrinsic piezoelectric response of ~1,000 pm·V<sup>-1</sup> and bias-stabilized pseudo-piezoelectric strains exceeding 10,000 pm·V<sup>-1</sup>. This behavior arises from a combination of large electrostriction (M = 1×10<sup>-14</sup> m<sup>2</sup>·V<sup>-2</sup>), ferroelastic softness, and structural reconfiguration, rather than intrinsic polarization switching. Multimodal characterization combining interferometry, diffraction methods, scanning probe microscopy, and first-principles modeling confirms the coupling between strain and metastable phase dynamics. These findings reveal a previously unrecognized mechanism for functional strain generation in fluorite oxides, positioning HZO as a versatile platform for strain-engineered actuators, adaptive metasurfaces, and reconfigurable nanoelectromechanical systems.</p>
