电畴结构对分子基铁电晶体电学性能的影响及其调控

As a kind of important functional materials, ferroelectrics have been extensively studied during the past few decades. A distinguished character of the ferroelectric material is that it contains multiple domain structures. It is known that the type, size, wall density, as well as evolution of the domain structures have significant effect on the electrical properties of the ferroelectric materials. Molecular ferroelectrics have attracted increasing interests in recent years due to their advantages of non-toxic, light weight, easy preparation and mechanical flexibility. In this proposal, the influence of domain structures on the electrical properties of molecular ferroelectric crystals will be studied. Several kinds of crystals, including croconic acid and diisopropylammonium salts, which exhibit excellent spontaneous polarization (Ps) and high phase transition temperature (Curie temperature, Tc), are chosen as the prototype. The evolution of both domains and phase structures under various temperatures and electric fields, as well as their influence on electrical properties will be investigated elaborately. Based on the experimental phenomenon, a valid physical model will be established to explore the inner mechanism. The properties of the crystals can be optimized by using domain engineering technique to control the domain configuration. This study will provide a theoretical and experimental guidance for promoting the practical application of molecular ferroelectric materials.

铁电体是一类重要的功能材料，其典型特征是具有电畴结构。电畴的类型、尺寸、畴壁密度、运动规律等对铁电体的宏观电学性能具有至关重要的影响。分子基铁电体具有无毒、轻便、易于制备、柔韧性好等优点，是近年来铁电材料研究领域的新兴方向。本项目拟从电畴结构的角度出发，以具有高自发极化强度（Ps）、高居里温度（Tc）的巴豆酸系列和二异丙胺卤离子盐系列分子基铁电晶体为研究对象，研究晶体内电畴结构对电学性能的影响。通过对变温和负载电场下晶体中电畴结构的形成与变化规律进行探讨，结合场致结构相变，分析晶体电学性能的产生和变化的影响因素。在此基础上，建立有效的物理模型，揭示晶体电畴结构对电学性能的影响规律和作用机制。利用畴工程技术调控晶体的电畴形态，实现晶体电学性能的优化，为促进分子基铁电材料的实用化提供理论依据和实验指导。

铁电体是一类在特定温度范围内具有自发极化，且自发极化可以在外场作用下重新取向的功能材料，在信息存储器、红外探测器、传感器和微驱动器等功能器件领域有着非常广泛的应用。分子基铁电体是以有机小分子或有机-无机杂化分子为基础的新型铁电材料，具有无毒、轻便、易于制备、柔韧性好等突出优点，是近年来铁电材料研究领域的新兴方向。本项目以新型分子基铁电体为研究对象，制备合成以巴豆酸系列、二异丙胺卤离子盐系列、钙钛矿系列等有机小分子或有机-无机杂化分子为结构单元的化合物体系，研究了材料的相结构、电畴结构、光学性能与电学性能。本项目对晶体中电畴结构的形成与变化规律进行了系统探讨，结合场致结构相变与性能变化，研究了晶体内电畴结构与性能的关系。研究发现，晶体在相变过程中，采用可变温的偏光显微镜可以明显观察到电畴结构的变化，介温图谱和差示扫描量热分析结果则可观察到对应的异常峰。相变过程中晶体电畴结构的变化与相结构及电学性能的变化相互对应，电畴结构的变化实际上是相结构变化以及电学性能发生变化的直观表现，为电学性能的产生和变化过程提供了微观的可视化依据。而通过观察电畴结构的变化过程，也可以判断性能的变化趋势。在相变时，为了降低退极化电场及极化强度的急剧变化所带来的不良影响，晶体中产生了180°电畴。通过建立相关理论模型，揭示了晶体电畴结构产生和发生变化的原因，以及其对电学性能的影响规律和作用机制，以此指导晶体性能的优化。