Local ±[001]_c off-centering nanoregions in silver niobate

As a typical lead-free antiferroelectric material, silver niobate has attracted much attention in recent years due to its excellent performance in energy storage. In this work, based on a spherical aberration–corrected STEM-high angle annular dark field technique, the sites of each cation column of pure silver niobate and Ta-doped silver niobate were quantitatively obtained. Besides conventional antiferroelectric displacements along the ±[1−10]c directions, B-site ions were found to also deviate along ±[001]c directions and form many local off-centering nanoregions, which may induce weak ferroelectricity, just like polar nanoregions in relaxed ferroelectrics. Such results will further increase our understanding of silver niobate in the microscopic view and may help explain some unsolved questions.