Engineering Small-Molecule Proton-Transfer Ferroelectrics by Crystal Structure Prediction: Design Limits at the...

Area of Science:

• Materials Science
• Organic Electronics
• Solid-State Chemistry

Background:

• Organic molecular ferroelectrics offer tunable properties for advanced electronics.
• Proton-transfer (PT) salts show promise due to low coercive fields and fast switching.
• Enhancing spontaneous polarization in PT ferroelectrics requires smaller molecules and specific crystal packing.

Purpose of the Study:

• To design novel organic ferroelectrics with enhanced dipole density using smaller molecular species.
• To investigate the feasibility of achieving monovalent PT salts with ferroelectric properties through crystal structure prediction (CSP).
• To identify stable proton-transfer pathways and ferroelectric crystal packings.

Main Methods:

• Employed crystal-structure prediction (CSP) to design potential ferroelectric materials.
• Utilized density functional theory (DFT) for computational analysis and ranking of candidate structures.
• Conducted experimental synthesis and characterization of selected acid-base combinations.

Main Results:

• CSP identified several crystal structures with proton-transfer capable hydrogen-bonding networks.
• Initial DFT calculations suggested three candidate ferroelectric and one antiferroelectric packing.
• Experimental studies confirmed CSP's ability to predict PT-capable motifs but yielded neutral cocrystals instead of desired ferroelectric salts.

Conclusions:

• Achieving ferroelectric monovalent salts is complicated by the stability of protonation states.
• Protonation state stability is highly sensitive to the chosen DFT exchange-correlation functional and vibrational free energy.
• While CSP can predict PT crystal packing, accurately predicting protonation state stability requires further refinement.