铁电材料电/力多热效应的局域表征及微结构关联

The solid-state cooling technology based on the electrocaloric effect in ferroelectric materials is the most feasible candidate for microelectronic devices. However, the magnitude of the temperature change currently does not satisfy the requirement for practical cooling applications. The temperature change of electrocaloric effect is resulted from the variations of polarization at the nanoscale, which offers a new opportunity for enhancing electrocaloric effect and multicaloric effect via stress tuning ferroelectric phase and domain structures. However, the current studies on electrocaloric effect in ferroelectric materials are focusing on macroscopic temperature changes, yet there is no effective experimental technique to simultaneously probe microstructures and localized electrocaloric response, which restricts the understanding on the mechanisms of electrocaloric effect. In order to overcome this problem, we seek to develop a novel experimental technique based on atomic force microscopy and an analysis method based on finite element calculations and topology optimization, which can be used to loading stress via atomic force microscopy tip, applying external localized electric field, probing microstructures and caloric response with analysis simultaneously. Then, we will investigate the electrocaloric, elastocaloric effects, and electrocaloric effect tuned by stress, and multicaloric effect using the new developed method by us. The correlations between these caloric effects and microstructures will be identified, and the mechanisms of these caloric effects will be unraveled, resulting in the new pathway for enhancing multicaloric effect, which can promote the applications of ferroelectrics in solid-state cooling technology.

基于铁电材料电热效应的固态制冷有望成为微电子设备制冷的理想方式，但当前其温变大小还不能满足实际应用的需求。电热效应温变的本质在于微观尺度极化的变化，这为应力调控铁电材料微观相结构和电畴结构、进而提升电热乃至多热效应性能带来新的机遇。然而当前铁电材料电热效应的研究集中在宏观尺度整体温变，仍然缺乏有效的实验手段同步关联材料微观结构和局域电热响应，因而限制了人们对电热效应微观机理的理解。基于此，本项目拟发展一套适用于铁电材料局域电/力热效应的新型原子力显微实验方法和有限元拓扑优化计算模型，同步实现探针力、局域电加载、材料微观结构表征、以及探针热响应测量与分析。以此为基础，将系统研究铁电材料电热、力热、应力调控电热、以及力电载荷下的电/力多热效应，建立起局域电/力热效应与铁电材料微结构的关联，深刻揭示出电/力所致热效应的微观机理，从而提出多热效应增强的新机制，推动铁电材料在固态制冷技术中的应用。

发展铁电材料热效应响应直接表征方法，建立铁电材料电/力热效应与微结构之间的关联，是理解铁电材料热效应微观机理和提升其热效应响应的关键，也是推动铁电材料在固态制冷技术中应用的基础。项目工作从实验表征方法的发展、实验表征研究、理论模拟分析三个方面，进行了铁电材料电热、力热、应力调控电热、以及电/力多热效应的研究。基于原子力显微技术，采用热探针，通过外接高精度惠斯通电桥等部件，发展了一套铁电材料局域热效应响应表征的新型原子力显微实验方法，建立了相应的有限元模型，结合有限元模拟，实现了铁电材料局域热响应温度变化的高精度表征。基于实验表征，有限元模拟、热力学和相场模拟等理论分析，以钛酸钡单晶、掺杂钛酸钡基多层电容、铌镁酸铅-钛酸铅固溶体、铁电共聚物等经典铁电体系为材料对象，研究了铁电材料电热、力热、力调控电热、电/力多热效应，区分了电热温变与漏电流引起的焦耳热温变，获得了材料区域温度变化的图像，并探究了微观电畴结构、相结构、取向、外电/力场、温度等因素对铁电材料电/力热效应响应的影响，建立了铁电材料热效应与其微观结构的关联，解释了影响铁电材料热效应温度变化的微观机理，提出了通过增加畴界密度、控制材料取向、电场加载方向、不同力学加载组合、力电加载组合、场致负电热等方式增强铁电材料热效应响应，并对制冷潜力较大的多层电容结构进行了结构优化。研究工作所发展的实验表征方法和推广的理论分析方法，为铁电材料热效应的研究提供了实验表征和理论分析手段，所揭示的微观机理加深了人们对铁电材料热效应机理的理解，所提出的方案可为增强铁电材料热效应响应指引方向。研究工作目前已在Nano Energy、International Journal of Solids and Structures、Applied Physics Letters等上发表SCI论文13篇，申请发明专利2项，获得软件著作权1项。