Improper antiferroelectricity in NaNbO<sub>3</sub>-based perovskites driven by antiferrodistortive modulation.
basic_science · Level V
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- Record sourced from PubMed, PMID 40595523.
- Also identified by DOI 10.1038/s41467-025-60568-w and PMC identifier 12219638.
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Abstract
Perovskite materials exhibit a wide array of fascinating properties arising from various structural instabilities and the interplay between them. Probing such instabilities demands the use of high-resolution, high-sensitivity characterization techniques to prototypical materials with minimized complexity. Here we present the discovery of unconventional improper antiferroelectricity driven by antiferrodistortive modulation in NaNbO<sub>3</sub>-based perovskites, using advanced scanning transmission electron microscopy conducted on compositionally engineered samples, with a focus on Mn-doped (Na<sub>0.65</sub>Ag<sub>0.20</sub>Ca<sub>0.15</sub>)(Nb<sub>0.85</sub>Ti<sub>0.15</sub>)O<sub>3</sub>. Contrary to the prevailing understanding that such octahedral-rotation-driven improper polarization requires symmetry breaking at the interfaces in layered perovskites, our observation indicates that it can also be enabled in non-layered perovskites, by modulated octahedral rotations following an alternating sequence of (a<sup>-</sup>b<sup>-</sup>c<sup>+</sup>)<sub>m</sub> (m = integer) and a<sup>-</sup>b<sup>+</sup>c<sup>+</sup> that is tunable via chemical doping. Combining with first-principles calculations and group theoretical analysis, we reveal a multimode interaction picture to generate the unique dipole order, resolving its long-standing structural ambiguity. The identified mechanism for octahedral-rotation-driven improper polarization represents a new design freedom to tailor the interplay of instabilities for coupled functionalities in perovskite oxides.