Room-Temperature Ferroelectricity in an Organic Cocrystal

Area of Science:

• Materials Science
• Organic Electronics
• Solid-State Physics

Background:

• Ferroelectric materials possess switchable polarization via electric field-induced symmetry breaking.
• Organic charge-transfer (CT) cocrystals typically utilize neutral-ionic transitions for ferroelectricity, but displacive behavior and high Curie temperatures (T_C) are rare.
• Existing design strategies for CT ferroelectrics have limitations in achieving ambient or above T_C.

Purpose of the Study:

• To design and characterize a novel organic cocrystal exhibiting displacive ferroelectricity.
• To achieve switchable remanent polarization in an organic CT cocrystal at room temperature.
• To explore alternative design principles beyond traditional CT interactions for ferroelectric cocrystals.

Main Methods:

• Synthesis and characterization of a cocrystal composed of acenaphthene (AN) and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane.
• Temperature-dependent Raman spectroscopy to probe structural and electronic transitions.
• X-ray diffraction (XRD) and solid-state Nuclear Magnetic Resonance (NMR) spectroscopy to elucidate the mechanism of ferroelectric switching.

Main Results:

• The novel AN-based cocrystal demonstrates switchable remanent polarization with a T_C of 68°C, operating above ambient temperature.
• Structural analysis indicates that ferroelectric behavior is driven by the rotation of acenaphthene molecules, a mechanism distinct from typical CT interactions.
• Experimental evidence confirms displacive ferroelectric behavior facilitated by molecular rotation, not charge-transfer transitions.

Conclusions:

• A new organic displacive ferroelectric cocrystal operating above room temperature has been successfully developed.
• The findings highlight the significance of non-CT interactions, specifically molecular rotation, in designing organic ferroelectrics.
• This work expands the design strategies for organic ferroelectric materials, potentially enabling new applications in electronic devices.