Novel Ferroelectric Polymers for High Energy Density and Low Loss Dielectrics
Novel Ferroelectric Polymers for High Energy Density and Low Loss Dielectrics
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DOI：
10.1021/ma2024057
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发表时间：
2012-04-10
期刊：
影响因子：
5.5
通讯作者：
Wang, Qing
中科院分区：
文献类型：
--
作者：
Zhu, Lei;Wang, Qing
在过去的几十年里，最先进的聚合物介电材料仅限于能量密度相对较低但介电损耗超低的非极性聚合物。随着电力电子技术在脉冲功率和功率调节应用领域的快速发展，在高能量密度/低损耗和/或高温/低损耗聚合物介质领域对下一代介质电容器的需求越来越大。鉴于进一步增强聚合物的原子和电子极化的局限性，本视角聚焦于一个基本问题：极性聚合物中的取向极化能否用于高能量密度和低损耗的介电材料？现有的实验和理论结果提出了以下观点。对于非晶态极性聚合物，在其玻璃化转变温度以下可以获得高能量密度和低损耗。对于液晶侧链聚合物，偶极迁移率很高，以至于它们在相对较低的电场下饱和，并且在偶极饱和后只能进一步存储有限的电能。结晶性极性聚合物具有广阔的应用前景，可分为三类：普通铁电材料、顺电材料和新型铁电材料。对于正常的铁电结晶聚合物，高自发极化的切换会导致很大的磁滞。为了减小电滞回线，需要超细的微晶或铁电畴来减小自发极化。对于顺电结晶聚合物，偶极子有可能在外部电场中排列。然而，对于高能量密度和低损耗的应用，要求具有高度的偶极可逆性。新的铁电行为包括弛豫铁电性和类反铁电性，因为它们具有高度的偶极可逆性。为了实现弛豫铁电行为，需要在晶格中引入体积较大的共聚单体等结构缺陷，以扩大横向晶胞尺寸，加快晶体偶极子的迁移率和可逆性。到目前为止，还没有发现真正的反铁电结晶聚合物。然而，这种反铁电行为是通过纳米限制降低补偿极化来实现的。未来还需要更多的研究来开发新型顺电和新型铁电聚合物，用于高能量密度和低损耗的介电材料。
The state-of-the-art polymer dielectrics have been limited to nonpolar polymers with relatively low energy density but ultralow dielectric losses for the past decades. With the fast development of power electronics in pulsed power and power conditioning applications, there is a need for next-generation dielectric capacitors in areas of high energy density/low loss and/or high temperature/low loss polymer dielectrics. Given limitations in further enhancing atomic and electronic polarizations for polymers, this Perspective focuses on a fundamental question: Can orientational polarization in polar polymers be utilized for high energy density and low loss dielectrics? Existing experimental and theoretical results have suggested the following perspectives. For amorphous polar polymers, high energy density and low loss can be achieved below their glass transition temperatures. For liquid crystalline side-chain polymers, dipole mobility is so high that they saturate at relatively low electric fields, and only limited electrical energy can be further stored after dipole saturation. Crystalline polar polymers are promising and can be divided into three categories: normal ferroelectric, paraelectric, and novel ferroelectric. For normal ferroelectric crystalline polymers, switching of a high spontaneous polarization results in a large hysteresis. To reduce the hysteresis, ultrafine crystallites or ferroelectric domains are desired to reduce the spontaneous polarization. For paraelectric crystalline polymers, dipoles have the potential to align in an external electric field. However, a high degree of dipole reversibility is required for the high energy density and low loss application. Novel ferroelectric behaviors include relaxor ferroelectric and antiferroelectric-like behaviors are highly desired because of their high degree of dipole reversibility. To achieve the relaxor ferroelectric behavior, structural defects such as bulky comonomers need to be introduced into the crystalline lattice to expand the lateral unit cell dimensions and speed up the mobility and reversibility of crystalline dipoles. So far, true antiferroelectric crystalline polymers have not yet been discovered. Nevertheless, the antiferroelectric-like behavior has been realized by reducing the compensation polarization via nanoconfinement. In the future, more research is needed to develop new paraelectric and novel ferroelectric polymers for high energy density and low loss dielectrics.