Coexistence of Ferroelectricity and Antiferroelectricity in a Photoactive Low-Dimensional Coordination Single-Phase Crystal

Single-crystal materials with coexistent ferroic orders (e.g., ferroelectricity and ferromagnetism) have shown intriguing physical properties for optoelectronic device applications. However, the inherent energy competition and symmetry incompatibility between ferroelectric and antiferroelectric orders pose a huge challenge to realize this coupling within a single-phase molecular system at the same temperature phase. Herein, we have designed a photoactive bismuth-based halide (BZA)₂(EA)BiBr₆ (<b>B-E</b>, where BZA⁺ is benzylammonium and EA⁺ is ethylammonium), which shows exceptional coexistence of multiaxial ferroelectric and antiferroelectric orders along different crystallographic directions, with a high curie temperature ∼380 K and spontaneous polarization of 2.5 μC/cm². Notably, its unique mixed-cation configuration containing BZA⁺ and EA⁺ cations allows the modulation of the dipole spatial arrangement and the free energy of electrical ordering. Based on the principle of symmetry breaking with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover><mml:mi>3</mml:mi><mml:mo>¯</mml:mo></mml:mover></mml:math><i>m</i>F2, the parallel alignment of dipole moments is stabilized along the [010] direction to create ferroelectric photovoltaic-pyroelectric behavior. Contrarily, the coexistence of antiparallel and parallel arrangements along the [<i>h</i>0<i>l</i>] directions ultimately induces a stable antiferroelectric state with strong phototunability. Such coexistent ferroelectric and antiferroelectric orders are sensitive to light stimulus, which offers a new pathway for the optical control of polarization switching. These findings expand the family of molecular electric-ordered materials and provide new insights for the assembly of high-performance electronic devices.