Ferroaxial transition in the glaserite compound NaBaCo(PO)

Kajita, Yoichi*; Yamagishi, Shigetada*; Hayashida, Takeshi*; Kimura, Kenta*; Hagihara, Masato   ; Kimura, Tsuyoshi*

Ferroaxial order is characterized by the symmetry breaking of the mirror parallel to the principal axis in the crystal structure. It is predicted to show unique physical properties such as the antisymmetric thermopolarization, that is, the induced-polarization perpendicular to the applied temperature gradient [1]. So far, materials showing ferroaxial order are limited. A recent study focused on the glaserite-type compounds belonging to the space group P-3 (No. 147) or P-3m1 (No. 164) as ferroaxial material candidates and experimentally confirmed that one of such compounds, KZr(PO) is a ferroaxial material [2]. In this work, we focus on one of the glaserite-type compounds, NaBaCo(PO). We synthesized polycrystalline samples by a solid-state reaction and single crystals by a flux method similar to the previous report [3]. We conducted measurements of thermogravimetry and differential thermal analysis (TG-DTA) for these samples and found the possibility that NaBaCo(PO) undergoes a phase transition at around 700 K. Through neutron powder diffraction measurements, we revealed that the phase transition is a ferroaxial transition from ferroaxial P-3; to nonferroaxial P-3m1. In the ferroaxial phase of NaBaCo(PO), there are two domain states depending on the sign of the order parameter, which corresponds to the rotational direction of the PO tetrahedron. Such domain states can be visible with the electrogyration, that is, the gyration induced by an applied electric field [4]. Using this technique, we attempted to visualize the ferroaxial domains in NaBaCo(PO). In this presentation, details of the experiments and results will be presented. [1] J. Nasu and S. Hayami, Phys. Rev. B 105, 245125 (2022).[2] S. Yamagishi et al., Chem. Mater. 35, 747 (2023).[3] R. Zhong et al., Proc. Natl. Acad. Sci. USA 116, 14505 (2019).[4] T. Hayashida et al., Nat. Commun. 11, 4582 (2020).