基于双弛豫相界区的高极化响应低损耗铁电材料研究

The ferroelectric materials applied in the area of high efficiency energy storage and precision actuator require a characteristic of both high polarization response and low energy loss. Normal ferroelectric materials possess high polarization, however, the high energy barrier and bistable state of its polarization response in the macro domain make a high remnant polarization and high energy loss; Relaxor ferroelectrics formed by doping ions can reduce the remnant polarization and energy loss due to its polarization response in the micro domain formed by the random local defect field, while the maximum polarization is also reduced due to the block of the local barrier on the polarization response. How to maintain the high polarization response and low energy loss at the same time is the key scientific problem. Based on the previous research results, present project proposes to construct a double relaxor phase boundary region - using the random local defect field from relaxor phase transition to reduce the remnant polarization, and using the low energy barrier of polarization response in the phase boundary region to make the maximum polarization being not blocked by the local energy barrier but switched to the long-range order value - thereby increasing the polarization response, meanwhile keeping low energy loss from the micro polar domains of the phase boundary and relaxor regions. Present project intends to choose lead-free ferroelectric system, to study the crystal component concentration at the double relaxor phase boundary region on the polarization response barrier to determine the maximum polarization response, to study the influence of the random local defect stress/electric field on the phase transition temperature to select the doping types with stable and low energy loss micro polar domains, and to study double relaxor phase boundary region constructed by different local crystal structure component in order to optimize the ability of the polarization response to the external field. Through the research work of the present project, a way to design high polarization response and low energy loss environmentally-friendly ferroelectric materials is provided, and the mechanism of the polarization response in the double relaxor phase boundary region is clarified, thus being of scientific and practical important significance.

应用于高效储能及精确驱动的铁电材料要求兼具高极化响应与低损耗。正常铁电体具有高极化强度，但极化宏畴响应的高能垒及双稳态导致剩余极化高且损耗大；通过掺杂形成弛豫铁电体，由缺陷局域场导致极化微畴响应可降低损耗且剩余极化小，但是也使最大极化受限于局部能垒而减小。如何兼具高极化响应与低损耗是其关键科学问题。申请人基于前期研究基础，提出构造双弛豫相界区-由弛豫相变中缺陷局域场降低剩余极化，并利用相界区的低能垒使最大极化不受限于局部能垒而转向长程有序-从而既提高极化响应，又兼有弛豫与相界区的极化微畴而能耗低。拟研究晶体成分浓度对极化能垒的影响以确定极化响应峰值；研究缺陷局域场对相变温度的影响以稳定损耗低的极化微畴；研究具有不同端点晶体结构组合的双弛豫相界区以优化极化响应能力。通过本项目的研究，为设计高极化响应低损耗环境友好铁电材料提供途径，并阐明双弛豫相界区极化响应机制，具有重要的科学和实际意义。

铁电材料具有高极化强度，通过掺杂后形成弛豫铁电体，宏畴转变为微畴可降低损耗，在脉冲功率系统高效储能及机电精确驱动方面具有重要的应用前景。但是铁电宏畴双稳态能垒与微畴局部能垒导致高极化强度与低损耗难以同时兼顾。本项目利用掺杂构建双弛豫相界铁电体系，主要研究晶体成分浓度，缺陷局域场及不同局部晶体结构组合对极化响应峰值及极化微畴稳定性的影响。从能垒及相变影响微畴翻转角度阐明双弛豫相界区极化响应机制，进一步基于高极化率组元及多相共存弛豫态的设计提升极化响应并降低损耗。.通过本项目的研究，制备了掺杂的弛豫铁电材料，通过成分调控获得了局部结构菱方和四方相共存的高效铋系储能体系，分析表明掺杂的高极化率组元不仅有益于保持高极化的菱方相及维持体系的高极化基因同时具有纳米极化微区的低损耗特点，在低场和中场下获得90%以上效率且储能密度高于其他体系的优异储能性能（Chem. Eng. J., 2022a；ACS Appl Mater Inter，2021）；利用缺陷调控铋系弛豫铁电体介电常数峰值，通过产生缺陷局域场获得弥散相变行为以稳定低损耗的极性纳米微区温度区间，获得了兼具高储能性能与优异温度稳定性的弛豫铁电体系，并采用压电力显微镜分析验证了极化微畴可逆翻转能力（Chem. Eng. J. 2022b; 2021）；利用不同局部晶体结构对称性共存的四相点设计制备了铋掺杂钡系弛豫铁电体系，其多相共存弛豫态区域不同极化态之间的低能垒有利于极化微畴翻转，并经由相场模拟及微观电镜阐明了极化低能垒及多相共存弛豫态演变机制，与体系大电致伸缩系数协同作用获得了几乎无迟滞的优异电致应变性能（Nano Energy，2021）。.研究工作共计发表国际期刊论文26篇，其中发表在Chem. Eng. J., Nano Energy，ACS Appl. Mater. Inter., J. Mater. Chem. A国际领域高水平期刊8篇；参加国际及双边学术会议并做报告7人次；国际交流联合培养博士2人次。研究结果为设计制备高效率高储能密度介电电容器及低滞后高应变精确驱动压电材料提供了新的途径，同时为深入理解掺杂影响弛豫铁电相变行为与极化响应能垒及微畴稳定性机制提供了思路。