Antiferroelectric Behavior in Mixed‐Anion Bi₂TiO₄F₂ Induced by Rotation of TiO₃F₃ Octahedra

Abstract Antiferroelectric materials, known for their structural transitions from paraelectric to ferroelectric phases under an electric field, have attracted significant interest due to their high energy storage capacity and rapid thermal conductivity switching capabilities. Traditionally, research on antiferroelectric properties has focused on modifying metal cations or crystal structures, with cation displacement playing a central role in the mechanism. However, antiferroelectric states have not been reported in mixed‐anion systems, where some oxide ions (O 2– ) are replaced by other anions such as nitride or fluoride (F – ). This study demonstrates that Bi 2 TiO 4 F 2 , a layered Aurivillius‐type oxyfluoride film, exhibits antiferroelectric behavior, undergoing structural transitions from non‐polar to polar phases under an electric field. Theoretical calculations reveal that this behavior is driven by the rotation of TiO 3 F 3 octahedra within the perovskite layers, leading to displacements of O 2– and F – ions along the c ‐axis due to their valence differences. Unlike conventional metal oxides, where antiferroelectricity is governed by cation displacements, oxyfluorides present a novel mechanism based on anion valence disparities. This finding paves the way for designing advanced antiferroelectric materials with mechanisms distinct from those of traditional oxides.