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<p>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 (<i>a</i><sup>−</sup><i>b</i><sup>−</sup><i>c</i><sup>+</sup>)<sub><i>m</i></sub> (<i>m</i> = integer) and <i>a</i><sup>−</sup><i>b</i><sup>+</sup><i>c</i><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.</p>

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Improper antiferroelectricity in NaNbO3-based perovskites driven by antiferrodistortive modulation

  • 期刊论文

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  • 发表日期：

    2025年7月1日

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  • Chao Xu,
  • Nengneng Luo,
  • Cenchen Zhong,
  • Gengguang Luo,
  • Ruoxuan Che,
  • Xuyun Guo,
  • Changsheng Chen,
  • Shujun Zhang,
  • Ye Zhu

摘要

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 NaNbO3-based perovskites, using advanced scanning transmission electron microscopy conducted on compositionally engineered samples, with a focus on Mn-doped (Na0.65Ag0.20Ca0.15)(Nb0.85Ti0.15)O3. 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−b−c+)m (m = integer) and a−b+c+ 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.