Precise Design of Organic–Inorganic Hybrid Indium Molecular Ferroelectrics Based on Halogen Substitution

Low-dimensional hybrid organic–inorganic ferroelectric materials have attracted significant interest due to their outstanding optical and electrical properties. Nevertheless, many of the most extensively studied organic–inorganic hybrids incorporate lead or tin, which raises concerns related to long-term stability and environmental sustainability. Here, by using the quasi-spherical strategy, we have designed and obtained a series of zero-dimensional organic–inorganic hybrid indium metal ferroelectric compounds: [Me₂CH₂X(i-Pr)N][InBr₄] (X = H, 1; F, 2; Cl, 3; Br, 4, respectively), based on halogen-substituted quaternary amines. The differential scanning calorimetry (DSC), dielectric, and second harmonic generation (SHG) measurement results show that these four compounds have high-temperature phase transitions (above room temperature). The ferroelectric properties of the compounds were confirmed through piezoresponse force microscopy (PFM) and electric hysteresis loop (P-E) measurements. This research offers new ideas for the advancement of ferroelectric materials and the innovation of future smart materials and optoelectronic devices.