Proton tautomerism for strong polarization switching

Area of Science:

• Materials Science
• Solid State Physics
• Organic Chemistry

Background:

• Proton tautomerism enables ferroelectric properties in organic crystals, promising for low-field and high-temperature applications.
• Organic ferroelectrics offer potential advantages over inorganic counterparts, but efficient switching of spontaneous polarization remains a challenge.

Purpose of the Study:

• To investigate seven organic ferroelectric crystals for efficient switching of strong spontaneous polarization.
• To optimize ferroelectric properties through domain wall depinning and explore the underlying mechanisms.

Main Methods:

• Solution growth of organic ferroelectric crystals.
• Thermal annealing and repetitive bipolar voltage pulses for domain wall depinning.
• Polarization measurements and comparison with first-principles calculations.
• Point-charge model and hydrogen-bond geometry analysis to understand cooperative effects.

Main Results:

• Optimized organic ferroelectric crystals demonstrated excellent switching performance after domain wall depinning.
• Achieved polarization comparable or stronger than polyvinylidene fluoride, with significantly weaker coercive fields.
• Croconic acid exhibited record polarization (30 μC cm⁻²) for organic systems, surpassing some commercial ferroelectrics (e.g., SrBi₂Ta₂O₉, BaTiO₃).
• Optimization reduced the discrepancy between experimental and calculated spontaneous polarization to below 15%.

Conclusions:

• Proton tautomerism in organic ferroelectrics can be harnessed for high-performance devices.
• Domain wall engineering via thermal annealing and electrical pulsing is crucial for unlocking efficient switching.
• The cooperative roles of proton transfer and π-bond switching govern the ferroelectric behavior, offering a pathway for designing advanced organic ferroelectric materials.