Nagai Takayuki, Mochizuki Yasuhide, Yoshida Suguru, Kimura Tsuyoshi
Department of Advanced Materials Science, University of Tokyo, Kashiwa 277-8561, Chiba, Japan.
Department of Materials Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, Meguro-ku 152-8550, Japan.
J Am Chem Soc. 2023 Apr 12;145(14):8090-8098. doi: 10.1021/jacs.3c00797. Epub 2023 Mar 29.
Ferroaxial order, characterized by a rotational arrangement of electric dipoles, attracts increasing attention in terms of a new family of ferroic orders. However, there has been no chemical guideline for exploring crystalline materials showing ferroaxial order, namely ferroaxial materials. Here, we present a chemical guideline grounded in staggered polyhedral connectivity, which we propose as a structural prerequisite for ferroaxial order, and the second-order Jahn-Teller (SOJT) theory extended from molecular orbitals to electronic band structures. Na-superionic conductors (NASICON) including Na(PO) ( = early-transition or post-transition metal) are identified as potential ferroaxial materials because of their staggered structures composed of O octahedra and PO tetrahedra. However, ferroaxial phase transitions hardly occur in some of the NASICON systems, which offers a platform to uncover a hidden factor playing an important role in driving this system into ferroaxial states. Our first-principles calculations demonstrate that a ferroaxial phase transition in NASICON systems occurs only when SOJT interaction is symmetrically allowed, that is, energy-lowering chemical bonds are formed as a consequence of the distortion. Our proposals would be not limited to NASICON systems but applicable to a variety of compounds and provide new insight into the exploration of displacive-type ferroaxial materials.
铁轴序以电偶极子的旋转排列为特征，作为一类新的铁性序受到越来越多的关注。然而，对于探索具有铁轴序的晶体材料，即铁轴材料，尚无化学指导原则。在此，我们提出一种基于交错多面体连通性的化学指导原则，我们将其视为铁轴序的结构先决条件，以及从分子轨道扩展到电子能带结构的二阶 Jahn-Teller（SOJT）理论。包括 Na(PO)（=早期过渡或后过渡金属）的钠超离子导体（NASICON）因其由 O 八面体和 PO 四面体组成的交错结构而被确定为潜在的铁轴材料。然而，在某些 NASICON 体系中几乎不发生铁轴相变，这提供了一个平台来揭示在驱动该体系进入铁轴态中起重要作用的隐藏因素。我们的第一性原理计算表明，NASICON 体系中的铁轴相变仅在 SOJT 相互作用对称允许时发生，即由于畸变形成了能量降低的化学键。我们的提议不仅限于 NASICON 体系，还适用于各种化合物，并为探索位移型铁轴材料提供新的见解。
