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>i</i>-Pr)N][InBr₄] (X = H, <b>1</b>; F, <b>2</b>; Cl, <b>3</b>; Br, <b>4</b>, 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.