Fascinatingly high saturation polarization and electric-field induced strain make bismuth–sodium–titanium (BNT) promising alternatives. Interestingly, significantly improved oxide-ion conductive capacity and ultrahigh asymmetric strain can be stimulated, both of which show great sensitivity to the non-stoichiometry introduced by either nominal acceptor doping or intrinsic Bi volatilization. The weakly bonded Bi–O covalency in the ferroelectrics plays an unexpected role in the functional diversity. The highly polarized Bi ions configured with lone pair electrons contribute to the off-centering of the coordination environment and varying bond lengths. The inconspicuous structural changes concerning the multifunctionality raise difficulty and necessity in recognizing the origin at both average and local levels. Herein, the structural evolution and defect formation at the lattice level are elaborated including oxygen-octahedral tilting, cation displacements, and their chemical environment by comparing with the nominal oxygen-deficient composition. The impedance, polarization, and strain responses are discussed in detail to reveal the local polar distortions and average disorder in the non-cubic polytypes. The lower symmetry of the spatial configurations and larger cation displacements are identified. Combined with the oxygen vacancy and defect dipole dynamics in the ferroelectric/strain/conductive performances, this work will arouse interest in Bi-based ferroelectrics in the search for their multifunctional applications.

中文翻译：

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非化学计量 BNT 铁电体多功能性的结构洞察


令人着迷的高饱和极化和电场诱导应变使铋-钠-钛 （BNT） 成为有前途的替代品。有趣的是，可以刺激显着提高的氧化物离子导电能力和超高不对称应变，这两者都对名义受体掺杂或本征 Bi 挥发引入的非化学计量表现出极高的敏感性。铁电体中弱键合的 Bi-O 共价在功能多样性中起着意想不到的作用。配置有孤对电子的高极化 Bi 离子有助于配位环境的偏心和键长的变化。关于多功能性的不明显的结构变化增加了在平均和局部水平上识别起源的难度和必要性。本文通过与标称缺氧成分的比较，详细阐述了晶格水平的结构演变和缺陷形成，包括氧八面体倾斜、阳离子位移及其化学环境。详细讨论了阻抗、极化和应变响应，以揭示非三次多型中的局部极性失真和平均无序性。确定了空间构型的较低对称性和较大的阳离子位移。结合铁电/应变/导电性能中的氧空位和缺陷偶极动力学，这项工作将引起人们对 Bi 基铁电体的兴趣，以寻找其多功能应用。