锆钛酸钡铁电陶瓷电卡效应及其机制研究

Developing new type of high performance electrocaloric materials and exploring the microscope mechanism of the electrocaloric effect (ECE) are spotlights to the researchers in the area of functional materials. ECE is the consequence of the thermal change induced by the electrical field related polarization change. However, it is hard to differentiate contributions from various polarizations of domain switch, transformation between macro-domain and nano-domain, and electric field induced dielectric polarization to the total electrocaloric response. Meanwhile, the microscope mechanism of the ECE is still unclear. In this proposal, the Ba(ZrxTi1-x)O3 (BZT) ferroelectric ceramics are adopted. Two special critical points are chosen, one is around x=0.15 where four phases coexists and the other is around x=0.20 where phase changes between relaxor and normal ferroelectricity, to prepare samples with different polarization states (normal ferroelectric, relaxor and paraelectric). Measure the electrocaloric response by direct and indirect methods, respectively and study the influence of the different polarization states on the indirect method in the same material system. Through comparing the differential dielectric constant and the dielectric constant under different electrical field measured with impedance analyzer, a new method to differentiate the contribution different kinds of polarization to the general electrical polarization response is proposed. Further, reveal the influence of different polarization responses to the ECE effect and clarify microscope mechanism of the ECE. Consequently, this proposal would promote the development of the new type of high performance electrocaloric materials and lay a good theoretical foundation for the design of the prototype electrocaloric refrigeration devices.

新型高性能电卡材料和电卡效应微观机制是当前功能材料领域的研究热点。电卡效应是电场引起极性材料极化改变而导致热量变化的效应，但目前一直难以区别电畴翻转、宏畴-微畴转变和电场诱导介电极化等不同类型极化响应对电卡响应的贡献，电卡效应的微观机制也不清晰。本项目以Ba(ZrxTi1-x)O3（BZT）铁电陶瓷为研究对象，设计弛豫铁电/普通铁电转变点区域（x=0.20）和四相共存点区域（x=0.15）两个特殊组分，制备具有不同极化态（普通铁电体、弛豫铁电体及顺电体）的BZT铁电陶瓷；分别采用间接法和直接法测量其电卡响应，在同一材料体系中研究极化态对间接法测量电卡效应的影响；提出通过比较微分介电常数和偏置电场下介电常数的差异，以区分不同类型极化响应的新方法，阐明不同极化响应对电卡效应的贡献，揭示BZT铁电陶瓷电卡效应的微观机制，为促进新型高性能电卡材料的研究和电卡制冷器件的设计奠定基础。

新型高性能电卡材料和电卡效应微观机制是当前功能材料领域的研究热点。电卡效应是电场引起极性材料极化改变而导致热量变化的效应，因此电场和温度场作用下铁电材料的极化响应和相变特性与材料的电卡效应密切相关。本项目围绕锆钛酸钡基铁电陶瓷（BZT）、锆钛酸铅基（PZT）、钛酸锶铅基（PST）、铁酸铋基（BFO）等多种铁电材料的组分设计、相变特性、电卡效应及产生机制开展了系统研究工作，并获得了一系列兼具良好电卡效应和温度稳定性的材料组分。分别采用间接法和直接法测试各类材料的电卡响应，结合微观结构表征和热力学理论，揭示了外场下不同类型铁电体的极化和相变特性对应的电卡响应的作用规律，证明弛豫铁电体是有利于获得。在以BFO-BT材料为代表的多种铁电材料体系中发现了大负电卡效应，探讨了不同类型负电卡效应的起源。本项目为促进新型高性能电卡材料的研究和电卡制冷器件的设计奠定基础。