Key Takeaways & Executive Findings
- •• • Room-temperature ferroelectricity in an organic cocrystal was demonstrated (Wiscons et al., Angew Chem Int Ed, 2018, 57: 9044–9047), enabling practical applications without cryogenic constraints. • • Replacing [BF4]− anions with larger bis(trifluoromethanesulfonyl)ammonium (TFSA) anions in host-guest inclusion compounds raises the Curie temperature (Tc) by increasing the transition energy barrier, as cited in the research text. • • Order-disorder transitions in strained SrTiO3 (Salmani-Rezaie et al., Phys Rev Lett, 2020, 125: 087601) and KNbO3 (Tan et al., Inorg Chem, 2021, 60: 7961–7973) illustrate critical role of order-disorder behavior in ferroelectricity, informing design of organic systems. • • Synergetic H-bonding and charge-transfer interactions in a self-assembled structure yield a room-temperature ferroelectric material with electric field-induced dipole switching and piezo/pyroelectric energy conversion (Deepak et al., Chem Mater, 2023, 35: 3316–3328), highlighting multifunctionality.
Abstract
Organic/molecular ferroelectrics exhibiting spontaneous polarization have attracted increasing attention due to their flexibility, light weight, low-temperature processability, environmental friendliness, and biocompatibility. Among them, organic donor-acceptor cocrystals, self-assembled from two or more components, offer new insights into ferroelectricity. This review systematically examines recent progress in organic donor-acceptor cocrystal ferroelectrics, focusing on microscopic origins of ferroelectricity, structure modulation strategies, and underlying mechanisms. Ferroelectric origin mechanisms, including intermolecular charge transfer, proton transfer, and order-disorder transitions, are analyzed in detail. Structure-property relationships in crystal engineering are summarized, and recent advances in theoretical simulations, experimental characterization techniques, and practical applications are introduced. Finally, current challenges and future research perspectives are outlined. The review highlights that weak intermolecular interactions often lead to low Curie temperatures (Tc), limiting practical applications. Strategies to enhance Tc involve introducing stronger molecular interactions to increase transition energy barriers. Notably, room-temperature ferroelectricity in organic cocrystals has been achieved, as demonstrated by Wiscons et al. (Angew Chem Int Ed, 2018, 57: 9044–9047). The review underscores the potential of organic cocrystal ferroelectrics for flexible and wearable electronics, while addressing the need for higher Tc and robust switching performance.
1. Introduction
Conventional inorganic ferroelectrics, such as lead zirconate titanate (PZT), dominate applications but suffer from heavy metal toxicity and brittleness, limiting their use in flexible and wearable electronics. Organic ferroelectrics offer a promising alternative due to their mechanical flexibility, low-temperature processing, and biocompatibility. However, many molecular ferroelectrics exhibit Curie temperatures (Tc) below room temperature, severely restricting practical deployment. The weak intermolecular interactions in these systems facilitate phase transitions to paraelectric states at low temperatures, resulting in low or absent Tc. To overcome this bottleneck, researchers have sought to introduce stronger molecular interactions, such as hydrogen bonding or charge transfer, to raise the energy barrier for phase transition and stabilize the ferroelectric phase at higher temperatures.
This review focuses on organic donor-acceptor cocrystals, which self-assemble from electron-rich donors and electron-poor acceptors. These systems exhibit ferroelectricity arising from mechanisms such as intermolecular charge transfer, proton transfer, and order-disorder transitions. By engineering the molecular components and their packing, it is possible to achieve room-temperature ferroelectricity, as demonstrated in recent studies. The review systematically analyzes the microscopic origins of ferroelectricity, structure-property relationships, and modulation strategies, providing a roadmap for designing high-performance organic ferroelectrics. It also highlights advances in theoretical simulations and experimental characterization, along with emerging applications in flexible electronics, sensors, and energy harvesting.
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Xin Wang, Shulei Chen, Tao Jin, Jing Zhang, Qichun Zhang (2026). Organic donor-acceptor cocrystal ferroelectrics: advances and perspectives. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3986-2
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Frequently Asked Questions
What are the primary mechanisms of ferroelectricity in organic donor-acceptor cocrystals, and how do they influence the Curie temperature?
The primary mechanisms include intermolecular charge transfer, proton transfer, and order-disorder transitions. Charge transfer and proton transfer typically lead to displacive-type ferroelectricity, while order-disorder transitions involve molecular reorientation. The Curie temperature (Tc) is influenced by the strength of intermolecular interactions; stronger interactions increase the energy barrier for phase transition, thereby raising Tc. For example, replacing [BF4]− with larger TFSA anions in host-guest systems increases Tc by hindering molecular motion.
How can room-temperature ferroelectricity be achieved in organic cocrystals, and what are the design principles?
Room-temperature ferroelectricity has been achieved by designing cocrystals with strong hydrogen bonding and charge-transfer interactions that stabilize the polar phase. For instance, Wiscons et al. reported a room-temperature ferroelectric cocrystal (Angew Chem Int Ed, 2018, 57: 9044). Design principles include selecting donor-acceptor pairs with complementary shapes and electronic properties, promoting directional interactions, and ensuring a polar space group. Additionally, introducing bulky ions or molecules can increase the transition barrier, raising Tc.
What are the key challenges in scaling up organic cocrystal ferroelectrics for industrial applications?
Challenges include achieving high spontaneous polarization and stable switching at room temperature, ensuring thermal and chemical stability, and developing scalable fabrication methods. Many organic ferroelectrics have Tc below room temperature, limiting their use. Additionally, the mechanical flexibility and low-temperature processing are advantages, but the long-term reliability and fatigue resistance under repeated electric fields need improvement. Cost-effective synthesis and integration into devices remain hurdles.
How do order-disorder transitions affect the ferroelectric properties in organic systems compared to inorganic perovskites?
In organic systems, order-disorder transitions often involve reorientation of molecular dipoles or conformational changes, leading to relatively low Tc due to weak intermolecular forces. In inorganic perovskites like KNbO3, order-disorder behavior is also critical, but the stronger ionic interactions typically result in higher Tc. For example, Tan et al. (Inorg Chem, 2021, 60: 7961) highlighted the role of order-disorder in KNbO3. In organics, engineering stronger hydrogen bonds or charge-transfer interactions can mimic the rigidity of inorganic lattices, raising Tc.
What are the potential applications of organic cocrystal ferroelectrics, and how do they compare to inorganic counterparts in terms of performance?
Potential applications include flexible sensors, actuators, non-volatile memory, and energy harvesting devices. Organic ferroelectrics offer advantages in flexibility, low weight, and biocompatibility, but often exhibit lower polarization and Tc compared to inorganics like PZT. However, recent advances have achieved room-temperature operation and decent polarization values. For example, Deepak et al. (Chem Mater, 2023, 35: 3316) demonstrated piezo- and pyroelectric energy conversion in a room-temperature ferroelectric cocrystal. While performance metrics may be lower, the unique properties enable applications where inorganic materials are unsuitable.
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