奥里维利乌斯CaBi2B2O9（B = Ta，Nb）中铁电性、极化和高电阻率的起源
The origin of ferroelectricity, polarization and high resistivity in Aurivillius CaBi2B2O9 (B = Ta, Nb)
AI总结：
研究双层奥里维利乌斯铁电体CaBi₂B₂O₉中铁电等特性起源，结合群论分析与第一性原理计算，发现铁电相源于特定模式凝聚，确定层间滑动是铁电结构机制并建立微观图景，为设计相关铁电氧化物提供理论指导。
AI中文摘要：
奥里维利乌斯层状氧化物是高温铁电和压电应用的重要候选材料。本文结合群论分析和第一性原理计算，系统研究了双层奥里维利乌斯铁电体CaBi₂B₂O₉（B = Ta，Nb）中铁电相变、极化、压电响应和本征电绝缘的起源。结果表明，\textit{A2$_1$am}铁电相源于极性模式和非极性氧八面体旋转/倾斜模式的协同凝聚，其$\Gamma_5^-$X$_2^+$X$_3^-$三线耦合显著降低了总能量并加深了铁电势阱。自发极化和各向异性压电响应主要由Bi₂O₂层和Ta/NbO₆八面体的协同位移决定，Bi离子对两者都有不可或缺的贡献。更重要的是，极性畸变可追溯到相邻Bi₂O₂层与类钙钛矿块之间的相对面内位移。由于这种位移是Bi₂O₂/钙钛矿块交替堆叠拓扑结构所固有的，且与钙钛矿层数无关，我们将层间滑动确定为奥里维利乌斯氧化物中铁电性的一种通用的、与层数无关的结构机制。我们的发现建立了一个统一的微观图景，将CaBi₂B₂O₉（B = Ta，Nb）中的结构畸变、铁电极化、压电响应和电子绝缘联系起来，并为设计具有高居里温度和强绝缘性能的层状铁电氧化物提供了理论指导。
英文摘要：
Aurivillius layered oxides are important candidates for high-temperature ferroelectric and piezoelectric application. In this work, we combine group theoretic analysis with first-principles calculations to systematically investigate the origin of ferroelectric phase transition, polarization, piezoelectric response, and intrinsic electrical insulation of the two-layer Aurivillius ferroelectrics CaBi$_{2}$B$_{2}$O$_{9}$ (B = Ta, Nb). The results show that the \textit{A2$_1$am} ferroelectric phase arises from the cooperative condensation of a polar mode and nonpolar oxygen octahedral rotation/tilting modes, whose the $Γ_5^-$X$_2^+$X$_3^-$ trilinear coupling substantially lowers the total energy and deepens the ferroelectric potential well. The spontaneous polarization and anisotropic piezoelectric response are governed primarily by the cooperative displacements of the Bi$_{2}$O$_{2}$ layers and Ta/NbO$_{6}$ octahedra, with Bi ions providing an indispensable contribution to both responses. More importantly, the polar distortion can be traced to the relative in-plane displacement between adjacent the Bi$_{2}$O$_{2}$ layer and the perovskite-like block. Because this displacement is intrinsic to the alternating Bi$_{2}$O$_{2}$/perovskite-block stacking topology and is independent of the number of perovskite layers, we identify interlayer sliding as a general, layer-number-independent structural mechanism for ferroelectricity in Aurivillius oxides. Our findings establish a unified microscopic picture linking structural distortions, ferroelectric polarization, piezoelectric response, and electronic insulation in CaBi$_{2}$B$_{2}$O$_{9}$ (B = Ta, Nb), and provide theoretical guidance for designing layered ferroelectric oxides with high Curie temperatures and robust insulating behavior.
