铁电和反铁电外延薄膜电卡效应的重要影响因素及其物理机理研究

Recently, electrocaloric effect (ECE) is one of the “hot spots” in the field of functional materials. ECE in ferroelectric materials shows great potential in realizing highly efficient and environment-friendly solid-state cooling devices. However, the adiabatic temperature change or the isothermal entropy change induced by ECE in bulk materials is very low, which strongly limits their practical applications in refrigeration devices. With the development of thin-film fabrication technologies, people have obtained giant ECE in ferroelectric and antiferroelectric thin films and achieved much larger ECE temperature changes (e.g., >10 K) than bulk materials. It is well known that the entropy and polarization properties of ferroelectric and antiferroelectric thin films are strongly influenced by some key factors, such as defect dipoles, strain, doping, electrode materials, size effect, polarization fatigue and so forth. However, there are still lack of systematic studies on these factors influencing ECE in ferroelectric materials, especially from the experimental point of view. In this project, ferroelectric and antiferroelectric thin films or ultrathin films will be prepared by using rf magnetron sputtering and pulse laser deposition techniques. Then, the effect of defect dipoles, strain, doping, electrode materials, size effects and polarization fatigue on ECE of these thin films will be systemically investigated. The physical origin of ECE in ferroelectric and antiferroelectric thin films will be unveiled. It is expected that our studies could provide a deeper understanding of ECE in ferroelectric and antiferroelectric thin films. This will help us find the ways to significantly enhance the ECE and achieve large ECE-induced temperature changes in in these thin-film materials. The successful execution of this project will provide a solid basis for a broad range of future industrial applications of electrocaloric devices.

电卡效应是当前功能材料领域研究的热点，在实现高效率和环境友好型固态制冷器件方面具有巨大的应用前景。因铁电陶瓷的电卡效应的绝热温变或等温熵变通常都很低，所以无法实现商业应用。随着薄膜制备技术的不断发展，人们在铁电或反铁电薄膜中发现了巨电卡效应，获得了较大的电卡温度变化（>10 K）。缺陷偶极子、应力或应变、掺杂、电极、尺寸效应和极化疲劳等因素对铁电或反铁电外延薄膜的熵和极化特性有很大的影响，然而这些因素对电卡效应的影响和调控却研究得很少。本项目拟采用磁控溅射和脉冲激光沉积等方法制备高质量的铁电或反铁电外延薄膜或超薄膜，然后系统地研究缺陷偶极子、应力或应变、掺杂、电极、尺寸效应和极化疲劳等因素对薄膜电卡效应的影响，揭示其物理机制。申请人期望在弄清其关键影响因素和物理机理的基础上，找到提升铁电和反铁电薄膜电卡效应的方法，获得更大的电卡温变，为高效稳定电卡制冷器件的大规模工业化应用奠定坚实的基础。

制冷在人们生活中扮演着非常重要的角色。最近电卡效应制冷得到了广泛关注。相比于传统气体压缩制冷技术，电卡制冷具有效率高、体积小、无噪音、无需对环境有害的制冷剂等优点。但是电卡制冷目前面临一些关键科学难题，例如铁电陶瓷电卡温变和电卡效率太低，工作温度窗口太窄，而薄膜热容量太小，等等。.为解决这些问题，项目负责人及其团队主要就以下几方面进行了研究：（1）缺陷调控反铁电薄膜及陶瓷中的巨正负电卡效应；（2）通过电场和温度的耦合，将反铁电薄膜的电卡工作温度范围拓展到液氮甚至液氦温度附近；（3）电制冷循环对铁电多晶薄膜电卡效应的影响及物理机理；（4）通过元素掺杂等手段提升了BaTiO3基铁电陶瓷的电卡效应。.本项目取得的重要结果和关键数据如下：.（1）通过引入缺陷对反转动力学和反铁电-铁电相变能垒进行调控，在PbZrO3反铁电外延薄膜中实现了巨正电卡(+30K)和高达-18.5 K的负电卡效应，后者为文献上报道的室温附近的最大值。.（2）在老化的Mn掺杂Pb(Zr0.2,Ti0.8)O3陶瓷中发现了室温附近巨正电卡效应（ΔT=0.55K），其奇异电卡效应被归因于缺陷偶极子的恢复力。.（3）通过电场和温度的耦合效应，将PbZrO3反铁电薄膜的电卡工作温度范围拓展到液氮甚至液氦温度附近，为电卡器件在超低温制冷的应用打开了一个新的局面。.（4）系统研究了电制冷循环对Pb0.92La0.08Zr0.65Ti0.35O3 多晶薄膜电卡效应的影响，该工作对于开发具有优异循环稳定性的电卡制冷器件具有重要指导意义。.（5）通过元素掺杂调控结构相变，同时利用产生的缺陷偶极子、相变弥散特性和多相共存产生的较低能垒，大大提升了BaTiO3基铁电陶瓷的电卡效应。.本项目系统研究了铁电和反铁电薄膜和陶瓷电卡效应的物理机理，发现了提升其正负电卡效应的新方法，大大提高了这些材料的电卡温变和效率。这些工作为提升铁电和反铁电薄膜及陶瓷材料的电卡效应做出了重要贡献，推动了电卡固态制冷器件的实用化进程，为其未来的大规模应用奠定了坚实的基础。通过本项目，项目负责人及其合作者共发表论文48篇（包括Nano Lett, Adv Fun Mater, Appl Phys Lett, Phys Rev Appl, J Mater Chem C等国际著名期刊），其中通讯作者文章40篇。培养博士生4名，硕士生8名。