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Updated: Aug 5, 2025
Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses
Published on: June 7, 2018
Chemical Aspect of Displacive-Type Ferroaxial Phase Transition from Perspective of Second-Order Jahn-Teller Effect:
Takayuki Nagai1, Yasuhide Mochizuki2, Suguru Yoshida3
1Department of Advanced Materials Science, University of Tokyo, Kashiwa 277-8561, Chiba, Japan.
Abstract:
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 NaM2(PO4)3 (M = early-transition or post-transition metal) are identified as potential ferroaxial materials because of their staggered structures composed of MO6 octahedra and PO4 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.
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