Ferroaxial Transitions in Glaserite-type Compounds: Database Screening, Phonon Calculations, and Experimental Verification

Abstract

The so-called ferroaxial transition characterized by a rotational structural distortion that breaks a mirror symmetry has gained growing interest in terms of a new class of ferroic state in crystalline materials. RbFe(MoO 4 ) 2 , which belongs to glaseritetype compounds, X (□;1) Y (□;2) [M(TO 4 ) 2 ], is one of the most representative materials showing a ferroaxial transition, i.e., ferroaxial materials. Considering a variety of glaserite-type compounds, we expect that they provide a good arena for ferroaxial materials. In this work, we explored new ferroaxial materials by formula-based screening using a regular expression search and the symmetry detection algorithm. As a result, we found that a glaserite-type compound, K 2 Zr(PO 4 ) 2 , is one of the promising candidates for ferroaxial materials. Experimentally, we demonstrate that K 2 Zr(PO 4 ) 2 shows a ferroaxial transition at about 700 K, which is well explained by ab initio phonon calculations. The ferroaxial nature of K 2 Zr(PO 4 ) 2 is further confirmed by the observation of its domain structures using a linear electrogyration effect, i.e., optical rotation in proportion to an applied electric field. Our work provides an effective approach to exploring ferroaxial materials.

Chemical Aspect of Displacive-Type Ferroaxial Phase Transition from Perspective of Second-Order Jahn–Teller Effect: NASICON Systems as an Example

“…To realize the ferroaxial order in crystalline materials, the “staggered structure”, where the nonequivalent coordination polyhedra are alternately connected, is required. Representative examples of such staggered structures in crystalline materials are the ordered-double or charge-ordered perovskite structure [Figure b] and a corner-sharing alternate structure of octahedra and tetrahedra (e.g., glaserite structure , ) [Figure c]. In these staggered structures, the magnitude of A i is no longer identical at neighboring polyhedra.…”

Ferroaxial Transitions in Glaserite-Type Na2BaM(PO4)2 (M = Mg, Mn, Co, and Ni)

“…A recent study on formula-based database screening using a regular expression search and symmetry detection algorithm predicted seven glaserite-type compounds as candidates for ferroaxial materials showing a pure ferroaxial transition. 15 It was experimentally demonstrated that one of them, K 2 Zr(PO 4 ) 2 , indeed shows a ferroaxial transition at about 700 K. 15 Thus, the glaserite-type compounds are promising platforms for searching for materials showing a pure ferroaxial transition.…”

Chemical Switching of Ferroaxial and Nonferroaxial Structures Based on Second-Order Jahn–Teller Activity in (Na,K)2Hf(BO3)2

“…13 These forms of progress have motivated studies for developing new ferroaxial materials and controlling the ferroaxial order. 14 More recently, it has been proposed that "staggered structure", with the nonequivalent coordination polyhedra connected alternately, is essential to the emergence of ferroaxial order. 15 Rotational distortions in crystalline materials with staggered structures induce ferroaxial order, which is ascribed to ferri-like arranged electric toroidal moments.…”

“…Furthermore, the presence of ferroaxial order has been experimentally demonstrated by visualizing the ferroaxial domains with measurements of second harmonic generation , and electrogyration . These forms of progress have motivated studies for developing new ferroaxial materials and controlling the ferroaxial order …”