多极轴分子基铁电体研究

To date, the field of ferroelectric random access memories (FeRAM) is mainly dominated by inorganic ferroelectric thin films like BaTiO3, which suffer from the issues of environmental harmfulness, high processing temperatures, and high fabrication costs. In these respects, molecular ferroelectrics with advantages such as environmental friendliness, ease of processing, biocompatibility and structural tunability are regarded as promising and viable alternatives or supplements to conventional inorganic ones. However, most of the molecular ferroelectrics are subject to the uniaxial nature, so that the corresponding thin films not only require oriented substrates but also exhibit poor polarization switching performances in contrast to the single crystals. Conversely, if molecular ferroelectrics are multiaxial ones with multiple equivalent polarization directions, like the inorganic ceramic ferroelectrics, a larger spontaneous polarization can be obtained in the corresponding polycrystalline sample after poling, allowing them to maintain excellent performance in the thin-film form. Obviously, the exploration of multiaxial molecular ferroelectrics and thin films will greatly promote the development of molecular ferroelectrics from basic research to practical applications. This project intends to design and select multiaxial molecular ferroelectrics based on the moieties which are easy to induce structural phase transitions, such as 1, 4-diazobicyclo(2, 2, 2)octane (dabco), and quinuclidine. Then by the fabrication of high-performance thin films, the device applications of molecular ferroelectrics are expected to be realized in the near future.

目前在铁电随机存取存储器（FeRAM）等领域应用最广的是钛酸钡等无机陶瓷铁电薄膜，但其不足之处在于对环境有害，加工温度以及成本过高。因此，具有无毒性、易加工、生物兼容性好、结构可调控性高等优点的分子铁电体成为有益补充或替代品。然而，分子基铁电体大多具有单轴特性，使得相应薄膜不仅需要选择与晶格匹配的基底来进行生长，极化翻转性能也要远远逊色于单晶样品。如果分子基铁电体能像无机陶瓷铁电体一样具有多极轴特性，即极化在电场作用下可以在多个可能方向间翻转，那么在多晶薄膜样品中就可以获得较大的剩余极化值。显然，多极轴分子基铁电体及薄膜的探索将大力推动分子基铁电体由基础研究迈向实际应用。本项目拟选取1,4-二氮杂二环[2, 2, 2]辛烷（dabco）、奎宁环等易引发结构相变的小分子阳离子为结构基元，结合介电性、铁电性等测量手段，设计并筛选出多极轴分子基铁电体，再制备性能优良的薄膜，为早日实现器件化应用做

铁电体是一类应用广泛的集合声、热、电、光、磁、力效应的重要多功能材料。目前应用最广的是钛酸钡等无机铁电体，但其不足之处在于对环境有害，加工温度以及成本过高。因此，具有柔性、易加工、环保、结构可调控性较高等优势的分子铁电体成为有益补充或替代品。如何以分子设计为主要手段实现多极轴分子基铁电体的可控合成和性能优化，制备高质量的铁电薄膜，为探索新型铁电器件提供支持，是将分子基铁电体由实验层面推向实际应用首要面对的关键科学问题。有机-无机杂化钙钛矿体系能综合无机材料的性质多样性和有机分子筑块的可剪裁性，其结构和性能均易于通过修饰无机金属骨架和有机阳离子来进行调控，在铁电体设计领域具有极大的发展潜力。本研究围绕“多极轴分子铁电体研究”这一主要研究目标，选择拥有结构多样性的一维、二维无机钙钛矿骨架和能够经历有序-无序变化的小分子有机阳离子，进行合理的剪裁或修饰，通过分子自组装获得一系列具有介电开关性和非线性光学效应等功能性的相变化合物，从中成功筛选出了具有多极轴特性的二维杂化钙钛矿铁电体[2-氟苄胺]2PbCl4，并探索铁电薄膜的制备和畴工程研究，以期推动分子基铁电材料的应用发展。