Coexistence of ferroelectric and ferrielectric phases in ultrathin antiferroelectric PbZrO₃ thin films

Abstract

Whereas ferroelectricity may vanish in ultra-thin ferroelectric films, it is expected to emerge in ultra-thin antiferroelectric films, sparking people’s interest in using antiferroelectric materials as an alternative to ferroelectric ones for high-density data storage applications. Lead Zirconate (PbZrO₃, PZO) is considered the prototype material for antiferroelectricity, and indeed, previous studies indicated that nanoscale PZO films exhibit ferroelectricity. The understanding of such phenomena from the microstructure aspect is crucial but still lacking. In this study, we fabricated a PZO film with thicknesses varying from 5 to 80 nm. Using Piezoresponse Force Microscopy, we discovered that the film displayed a transition from antiferroelectric behavior in the thicker areas to ferroelectric behavior in the thinner ones, with a critical thickness between 10 and 15 nm. In this critical thickness range, a 12 nm PZO thin film was chosen for further study using aberration-corrected scanning transmission electron microscopy. The investigation showed that the film comprises both ferroelectric and ferrielectric phases. The ferroelectric phase is characterized by polarization along the [011]_pc projection direction. The positions of Pb, Zr, and O were determined using the integrated differential phase contrast method. This allowed us to ascertain that the ferroelectric PZO unit cell is half the size of that in the antiferroelectric phase on the ab plane. The observed unit cell is different from the electric field-induced ferroelectric rhombohedral phases. Additionally, we identified a ferrielectric phase with a unique up-up-zero-zero (↑↑··) dipole configuration. The finding is crucial for understanding the performance of ultrathin antiferroelectric thin films and the subsequent design and development of antiferroelectric devices.

Keywords

(Anti)ferroelectric / ferrielectric / lead zirconate (PbZrO₃) / thin films / scanning transmission electron microscopy

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