铁电复合材料的界面耦合及其电卡效应调控机制研究

The electrocaloric effect, i.e., the reversible entropy and temperature changes of a ferroelectric material upon the application and removal of an electric field, can be used for heat transportation and cooling. Refrigerators based on the electrocaloric materials can be exploited as an alternative to the conventional high-energy-consumption cooling devices, due to their superior cooling efficiency and more importantly, elimination of the environmentally harmful refrigerants. The electrocaloric composites integrate the advantages of the inorganic ferroelectrics (e.g. high electrocaloric strength) and the ferroelectric polymers (e.g. strong electrocaloric response), whose electrocaloric properties can be further improved by rationally regulating the inorganic-organic interfacial coupling effect. Due to the special connection among the electrical, thermal and mechanical properties in the electrocaloric effect, this proposal breaks through the limitations of previous studies that only take the electric polarization coupling into consideration. The project will systematically investigate the interfacial coupling effect on the thermal and mechanical properties, and reveal the influence rule of the co-effects of the thermal and mechanical characteristics on the polarization property and electrocaloric performance. Subsequently, the regulation mechanism of the thermal and mechanical interfacial coupling effects which can be tuned by modifying the microstructure will be explored, and the optimum microstructure of the electrocaloric composites will be systematically designed. Based on the guidance of the theoretical investigation and the microstructure design, the optical-controlling-liquid-crystal-assistance and other methods will be conducted to precisely control the microstructure of the composites. Eventually, the ferroelectric composites with high electrocaloric properties, whose comprehensive performances can meet the requirements of the environment-friendly cooling devices, will be fabricated. The investigation is of great significances for the theory exploration and performance optimization of the electrocaloric composites.

电卡效应利用电场来激发铁电材料的熵变和温变，进而实现热搬运和制冷。基于电卡材料的制冷器效率高、无需危害环境的制冷剂，有望取代现有的高能耗制冷设备。复合电卡材料兼具无机铁电体电卡强度大和铁电聚合物电卡效应强的优点，其性能的进一步提高依赖于无机-有机界面耦合效应的全面调控。本项目针对电卡效应中电、热和应力因素间的特殊联系，突破铁电复合材料研究中仅关注界面电极化耦合的局限，拟深入研究界面效应对复合材料各成分的热和应力特性的耦合机理,揭示界面处热和应力的协同作用对材料极化性能和电卡效应的影响规律；在此基础上，探索材料微结构变化对界面处热和应力耦合效应的调控机制，系统设计复合材料的最佳微结构；根据微结构设计，提出通过光控液晶辅助取向法等准确控制复合材料中无机铁电填充物的形貌和取向，最终制备面向新型制冷应用的高性能复合电卡材料。研究对复合材料电卡效应的理论探索和性能优化具有重要意义。

电卡效应利用电场来诱导铁电体的偶极熵变、控制材料的吸/放热过程，进而实现热搬运和制冷。电卡制冷无需危害环境的制冷剂，制冷效率更是传统压缩机制冷的2-5倍，且具有体积小和重量轻的特点，可用于大功率电子设备的散热降温，并有望取代基于压缩机的高能耗制冷技术。已有的无机和有机铁电材料均有其自身难以克服的问题：无机材料中，陶瓷和单晶块体的抗击穿场强低；陶瓷厚/薄膜抗击穿场强大，但膜材料体量小、吸热能力有限。铁电聚合物电卡效应强、抗击穿场强高、柔性好，但电卡强度低，致使理想的电卡效应需要较大电场来激发。项目提出研究无机—有机复合电卡材料，以期待通过界面效应调控来综合两者的优势。已有研究较多地关注了复合材料界面的电耦合极化，但电卡效应涉及电场对铁电体相变、偶极子取向、熵变和温变，直至吸、放热过程的一系列调控，除电极化耦合外，深入研究界面对无机和有机材料热和应力因素的耦合作用也至关重要。针对电卡效应中电、热和应力因素间的特殊联系，项目突破了铁电复合材料研究中仅关注界面电极化耦合效应的局限，深入研究了复合电卡材料界面对其各成分热和应力特性的耦合与传递机理，探索了界面处热和应力的协同作用对复合材料极化特性和电卡效应的影响规律；在此基础上，研究了微结构变化对复合材料界面耦合效应的调控机制，设计了复合电卡材料的微结构，通过微结构变化来优化复合材料的电、热和应力的协同耦合特性、提升材料的电卡效应。根据理论研究，结合典型的纳米材料制备工艺，制备了微结构合理、电卡效应较强的高性能复合电卡材料，使其电卡效应高于已有的无机和有机铁电材料，如电卡强度达到无机铁电陶瓷的2倍以上，且超过铁电聚合物一个数量级。研究为新一代节能环保型制冷材料与技术的实用化提供了指导。