A novel zero-dimensional germanium-based ferroelectric hybrid material with dual phase transitions

Abstract

Organic-inorganic hybrid ferroelectric materials have attracted much attention due to their structural tunability and functional versatility. While lone-pair stereochemical activity in elements such as Sb, Bi, and Pb has been widely used to design ferroelectrics, Ge²⁺ with a polar 4s² lone-pair remains underexplored. Herein, a novel zero-dimensional hybrid ferroelectric [(CH₃)₄N]GeBr₃ (1) was successfully synthesized by utilizing the stereochemically active lone pair of Ge²⁺. Compound 1 exhibits remarkable ferroelectric characteristics, including a large spontaneous polarization (P_s = 4.80 μC/cm²) and a low coercive field (E_c = 5.2 kV/cm). Moreover, the experimental results demonstrate that 1 undergoes dual structural phase transitions at 236 K and 453 K. The low temperature phase transition at 236 K belongs to the mmmFmm2-type ferroelectric phase transition. Remarkably, 1 undergoes a reconfiguration phase transition at 453 K, accompanied by the dimensional transformation from zero-dimensional to pseudo-three-dimensional architecture and giant dielectric switching behaviour. This work establishes new structure-property correlations in hybrid ferroelectrics while uncovering emergent technological potential in smart switching devices.