Off-stoichiometry of perovskite structural Bi_0.5Na_0.5TiO₃ (BNT) ferroelectrics can give rise to considerable oxide-ion conductivity. The inherent structural characteristics are urgent to be resolved due to its particular sensitivity of the conduction mechanism to the nominal composition and synthesis process. Herein, a thorough study of the temperature-dependent neutron, X-ray diffraction and Raman spectrum is carried out on a series of equivalently substituted A-site deficient non-stoichiometric and pristine BNT. Phase transition and defect association are systemically investigated in these dominated rhombohedral phases at room temperature, associated with well saturated ferroelectric states. Significant structural evolution identified by Rietveld refinements and the origin of the electrical performance are clarified at elevated temperatures, focusing on the subtle distortions of ionic displacements, oxygen octahedral tilts and local chemical environments for oxygen vacancies. The ion migration ability mediated by oxygen vacancies that are not energetically favorable in BNT mainly depends on the external substitutional disorder, and is strongly affected by the dopant concentration. Together with the lone pair substitution concept, superior oxide ionic conductivity is achieved, and an alternative strategy is provided in designing BNT based oxide ion conductors.

钙钛矿结构的非化学计量比 Bi _0.5 Na _0.5 TiO ₃(BNT) 铁电体可以产生相当大的氧化物离子电导率。由于其传导机制对标称成分和合成过程的特殊敏感性，其固有的结构特征亟待解决。在此，对一系列等效取代的 A 位缺陷型非化学计量和原始 BNT 进行了对温度依赖性中子、X 射线衍射和拉曼光谱的深入研究。在室温下，系统地研究了这些主要的菱面体相中的相变和缺陷关联，与充分饱和的铁电态相关。Rietveld 改进确定的显着结构演变和电气性能的起源在高温下得到澄清，重点是离子位移的细微变形，氧空位的氧八面体倾斜和局部化学环境。在 BNT 中，由在能量上不利的氧空位介导的离子迁移能力主要取决于外部取代无序，并且受掺杂剂浓度的强烈影响。结合孤对取代概念，实现了优异的氧化物离子电导率，并为设计基于 BNT 的氧化物离子导体提供了一种替代策略。