Precise structure and polarization determination of Hf_0.5Zr_0.5O₂ with electron ptychography

Hf_0.5Zr_0.5O₂ emerges as a promising candidate for next-generation ferroelectric memories and transistors. However, the intrinsic nature of its ferroelectricity remains a subject of debate, primarily stemming from challenges in the precise characterization of nanoscale polycrystallinity and multiphase coexistence. Here, we investigate substrate-free Hf_0.5Zr_0.5O₂ films using multislice electron ptychography, achieving a resolution of 25 picometers with capabilities for oxygen imaging, depth resolution, and vacancy quantification. Precise measurements reveal that the polarization displacement in ferroelectric phase is ∼56 ± 6 picometers (corresponding to a polarization ∼34 ± 4 μC/cm²). We further identify significant polarization suppression near grain boundaries, while there is negligible change in the 180° neutral domain walls. Furthermore, we demonstrate the existence of the 180° head-to-head charged domain wall in Hf_0.5Zr_0.5O₂, which is confined within a single unit cell layer. At such a charged domain wall, the atomic displacement is reduced to ∼4 picometers, with oxygen vacancies accumulating up to 20%. Notably, the polar layers neighboring the 180º head-to-head charged domain wall remain unchanged. The precise determination of these structural features with ultra-high spatial resolution offers critical information for optimizing and designing new hafnium-based ferroelectric devices.