反铁电和多铁薄膜的极化疲劳和反转动力学研究

Currently, antiferroelectric and multiferroic thin films are two "hot spots" in the field of functional materials. They may find their broad applications (or potential applications) in a variety of electronic devices, such as memories, sensors, actuators, energy-transformation devices and energy-storage devices, etc. However, there are still many fundamental questions that have not been solved properly, among which the mechanism of polarization fatigue and that of switching kinetics are two extremely important issues. In the past few years, the applicant has made significant contributions on the topics of polarization fatigue and switching kinetics in ferroelectric materials. These include, but not confined to: (1) experimentally, successfully explaining the phenomenon of polarization fatigue in ferroelectric devices, which has confused the scientists in this field for more than half a century, (2) establishing the LPD-SICI model for polarization fatigue in ferroelectrics (LPD-SICI stands for local phase decomposition induced by switching-induced charge injection), (3) establishing a statistical and stochastic theory for switching kinetics of ferroelectrics, etc. Based on what we did previously, the current project will start from a few representative antiferroelectric materials (e.g., PbZrO3-based antiferroelectric thin films) and multiferroic materials (e.g., BiFeO3-based multiferroic thin films). We will carry out a systematic investigation on the mechanisms of polarization fatigue, switching kinetics and their relationship in these two types of materials. We hope that we could eventually find out the methods of solving electrical fatigue and improving the switching speed of these devices when their mechanisms are fully understood after extensive studies. The successful execution of this project will provide a solid basis for a broad range of future industrial applications of antiferroelectric and multiferroic thin-film devices.

反铁电和多铁薄膜是当前功能材料领域研究的热点，在内存、传感器、致动器、换能器和储能器等方面有着非常广泛的应用。但是，这些材料中有两大基础性问题还没有得到很好的解决，即极化疲劳失效机理和反转动力学机制。过去几年，申请人在铁电体的极化疲劳和反转动力学方面均取得了一些具有突破性的成果，包括：（1）实验上，成功解释了困扰铁电领域科学家们达半个多世纪之久的铁电体极化疲劳现象；（2）创立了LPD-SICI极化疲劳模型；（３）创立了随机统计的铁电极化反转理论，等等。在前期工作基础上，本项目拟从几类代表性的反铁电材料（比如PbZrO3基反铁电薄膜）和多铁材料（比如BiFeO3基多铁薄膜）入手，对其电疲劳机理，极化反转机制以及它们之间的关联进行系统地研究。我们期望在弄清楚其物理机理的基础上，找到解决其极化疲劳的方法，获得提高其极化反转速度的手段，为反铁电和多铁薄膜器件的大规模工业化应用奠定坚实的基础。

铁电、反铁电和多铁材料是当前功能材料领域研究的热点之一。因具有良好的铁电性、压电性、热释电性和电光等特性，铁电和反铁电材料被广泛应用于内存、传感器、致动器、换能器和储能器件等电子元件。而多铁材料因其较大的磁电耦合特性，是近期非常热门的一种功能材料。但是，铁电、多铁和反铁电材料中有两大重要物理现象目前人们还了解的不是很清楚，即：极化疲劳和翻转动力学。.在本项目中，项目负责人及其团队主要就以下几个方面进行了系统的研究：（1）反铁电和铁电等材料的极化疲劳现象；（2）铁电和反铁电材料中的极化翻转；（3）外加电场驱动下，铁电和反铁电材料的极化变化及其材料体系熵的变化，即电卡效应（正电卡或负电卡效应）。.本项目获得的重要结果和关键数据如下：.（a）提出了一个极化疲劳“有效电压”的概念，指出：在通常条件下，决定铁电或反铁电薄膜极化疲劳的电场既不是交流驱动信号的最大电压，也不是“平均电压”，而是其“有效电压”；发现其可逆和不可逆瑞利系数都随着极化疲劳次数的增加而逐步减小，从而提出了一种通过测量瑞利系数来探测薄膜器件极化疲劳状态的新方法。.（b）研究了极化疲劳对PZT铁电薄膜器件光伏效应的影响。通过研究极化疲劳对PZT铁电薄膜器件光伏效应的影响，项目负责人发现其开路电压和闭路电流都随着疲劳次数的增加而逐步减小，利用LPD-SICI 理论，项目负责人很好地解释了上述实验现象。.（c）首次预言了BaTiO3铁电超薄膜中的巨弹卡效应；系统研究了无铅铁电陶瓷的巨电卡效应。系列论文发表在Adv Mater, Appl Phys Lett和Phys Rev B等国际著名学术期刊，被引200多篇次。.本项目的研究结果对科学家们正确理解铁电、反铁电和多铁材料中的极化疲劳、翻转动力学及电卡效应具有非常重要的意义。相关文章发表后，立即获得了本领域科学家们的广泛关注和引用（详见正文部分）。通过本项目，项目负责人及其合作者共发表SCI论文42篇，其中通讯作者文章30篇。培养博士生2名，硕士生4名。