Superior\nPiezo-/Ferro-Electricity in Antiferroelectric\nAg<sub><i>x</i></sub>NbO<sub>3‑δ</sub> Thin\nFilms by Nanopillar Local Structure Design

Antiferroelectrics\nare fundamental mother compounds critical in\ndeveloping innovative lead-free piezoelectrics and ferroelectrics\nand hold great promise for wide-ranging applications in energy conversion\nand electronic devices. However, harnessing their superior properties\npresents a significant challenge due to the delicate balance required\nbetween their various states. In this study, through the unique design\nof nanopillar structures to alleviate the local polar heterogeneity,\nwe have achieved significantly improved piezo-/ferro-electricity in\nclassic lead-free antiferroelectric Ag<sub><i>x</i></sub>NbO<sub>3‑δ</sub> (<i>x</i> = 1, 0.9, and\n0.8) epitaxial thin films. The effective piezoelectric coefficient\nreaches 440 pm V<sup>–1</sup>, 1 order of magnitude larger\nthan the stoichiometric AgNbO<sub>3</sub>, rivaling classic lead zirconate\ntitanate piezoelectrics. Atomic-scale electron microscopy investigations\nunravel the underlying mechanisms. The nanopillars, characterized\nby antisite occupancy of both Ag and Nb atoms and forming out-of-phase\nboundaries with the matrix, reduce the local crystal symmetry via\ninterphase strain. This leads to the creation of flexible multinanodomain\nstructures that significantly facilitate polarization rotation, thus\nsubstantially enhancing the piezoelectric performance. This study\ndemonstrates the feasibility of engineering local heterogeneity through\nnanopillar design, offering a generally applicable method for property\nimprovement of a wide range of antiferroelectrics.