SusChEM: Nanoscale Insight into Electric Fatigue of Lead-Free Piezoelectric Ceramics

非技术描述：铅会干扰许多身体过程，包括神经系统的发育，因此对儿童特别有害，并可能导致永久性学习和行为障碍。自20世纪70年代以来，限制铅使用的法规，如强制回收汽车铅酸电池和禁止使用含铅汽油和含铅油漆，大大减少了发达国家的铅暴露。然而，铅是世界上产量最大的金属之一，目前仍广泛用于各种产品。即使在今天，就接触铅中毒的人数和对公众健康造成的损害而言，铅中毒仍然是最大的环境医学问题之一。在电子设备和医疗器械中，铅主要用于压电元件。这些元件将电信号转换为声学信号，对于水下通信和超声医学成像至关重要。为了进一步减少铅污染，为子孙后代创造一个可持续的环境，目前使用的含铅压电材料必须被无铅材料取代。这个基础研究项目旨在为价值数十亿美元的压电业确定环境友好型组合物。这一成果有可能极大地惠及人类健康和环境。技术细节：压电器件的核心元件由含铅60wt%以上的锆钛酸铅陶瓷制成。铅的毒性引起了严重的环境问题，限制其使用的立法推动了世界范围内对无铅压电材料发展的广泛研究。在过去十年中，在成分设计和工艺控制方面取得了重大进展，目前正在推动研究界将这些科学成果转化为富有成效的、对环境无害的产品。因此，与性能稳定性和设备可靠性相关的基本问题需要立即彻底解决。在实际设备中，在使用过程中，这些陶瓷几乎总是受到循环的电动力或机械力的驱动，最终它们的性能会因疲劳而恶化。电疲劳退化是影响无铅陶瓷压电器件稳定性和可靠性的主要问题。在这个项目中，爱荷华州立大学的研究人员首次通过在透射电子显微镜内对无铅陶瓷试件进行电循环来研究电疲劳的微观结构机制。这种创新的现场研究可以确定导致快速疲劳退化的主要微观结构特征，因此，将有助于找到缓解性能退化的方法。然后，无铅化合物可以在广泛的工程和医疗技术中取代锆酸铅钛酸铅，这极大地有助于为儿童创造一个可持续的未来。该项目还旨在通过对学生进行尖端材料研究技术培训，对研究生和本科教育产生广泛影响。此外，一款关于铅毒性的iPad应用程序正在开发中，用于向高中生和本科生演示。

NON-TECHNICAL DESCRIPTION: Lead interferes with many body processes, including the development of the nervous system, and therefore is particularly toxic to children, and can cause permanent learning and behavior disorders. Regulations restricting lead use, such as enforced recycling of lead-acid batteries of automobiles and the ban of leaded gasoline and lead paint, have greatly reduced lead exposure in the developed world since the 1970s. However, lead is one of the most produced metals in the world and is still widely used in various products. Even today, lead poisoning remains one of the largest environmental medicine problems in terms of numbers of people exposed and the public health toll it takes. In electronic devices and medical instruments, lead is primarily used in piezoelectric elements. These elements convert electrical signals into acoustic signals and are critical for underwater communications and ultrasound medical imaging. To further reduce lead contamination and create a sustainable environment for future generations, currently used lead-containing piezoelectric materials must be replaced by lead-free ones. This project on fundamental research aims to identify environmentally-friendly compositions for the multi-billion dollar piezoelectrics industry. The outcome has the potential to greatly benefit both human health and the environment. TECHNICAL DETAILS: The core elements in piezoelectric devices are made of lead zirconate titanate ceramics, which contain more than 60 wt.% of lead. The toxicity of lead has raised serious environmental concerns and legislations on restriction of its use have driven extensive worldwide research on the development of lead-free piezoelectric materials. Significant progress has been made in the past decade in composition design and processing control and the research community is now being prompted to move these scientific achievements into fruitful environmentally safe products. As such, fundamental issues related to performance stability and device reliability need to be addressed thoroughly and immediately. In real devices during service, these ceramics are almost invariably driven by cyclic electric or mechanical forces, and eventually their performances deteriorate due to fatigue. Electric fatigue degradation is the major concern for stability and reliability of piezoelectric devices utilizing lead-free ceramics. In this project, the researchers at Iowa State are investigating the microstructural mechanisms of electric fatigue through electrically cycling lead-free ceramic specimens inside the transmission electron microscope for the first time. Such innovative in situ studies can identify the primary microstructural feature that leads to fast fatigue degradation and therefore, will help find ways to alleviate the property degradation. Lead-free compositions can then replace lead zirconate titanate in a wide range of engineering and medical technologies, which greatly help to create a sustainable future for children. This project is also designed to have a broad impact on graduate and undergraduate education by training students in cutting-edge materials research techniques. Furthermore, an App for iPads on the toxicity of lead is under development for demonstrations to high school students and undergraduate students.