Fluorination-Induced Room-Temperature Ferroelectricity in a Quasi-spherical Bismuth(III) Bromide Hybrid

Area of Science:

• Materials Science
• Solid-State Chemistry
• Crystallography

Background:

• Molecular fluorination is a precise strategy for enhancing material properties.
• Halogen engineering impacts rotational energy barriers and dipole moments.
• Ferroelectric materials are crucial for electronic applications.

Purpose of the Study:

• To investigate the effect of fluorination on the properties of a quasi-spherical amine bismuth(III) halide compound.
• To synthesize and characterize a novel fluorinated ferroelectric material.
• To demonstrate fluorination as a viable molecular design strategy for new ferroelectrics.

Main Methods:

• Synthesis of fluorinated and non-fluorinated bismuth halide compounds.
• Variable-temperature single-crystal X-ray diffraction (SC-XRD).
• Differential scanning calorimetry (DSC), second-harmonic generation (SHG), polarization-electric field (P-E) hysteresis loops, and piezoelectric force microscopy (PFM).

Main Results:

• A room-temperature ferroelectric compound, [1,4-3.2.2-H2dabcn-CH2F][BiBr5] (1 F), was successfully synthesized via fluorination.
• The nonfluorinated analogue [1,4-3.2.2-H2dabcn][BiBr5] (1) was found to be nonferroelectric.
• Compound 1 F exhibits ferroelectricity in the orthorhombic system (space group Pca21) with a saturation polarization (Ps) of 2.23 μC/cm² and confirmed piezoelectric properties.
• Phase transition from ferroelectric to paraelectric phase was confirmed via variable-temperature characterizations.

Conclusions:

• Fluorination is a potent molecular design strategy for developing novel ferroelectric materials.
• The synthesized compound 1 F demonstrates significant ferroelectric and piezoelectric properties.
• This work opens new avenues for exploring advanced functional materials through precise molecular engineering.