伪弛豫铁电行为特性的研究及其调控

The pseudo-relaxor behavior created by interfacial polarization behaves as the same as that of relaxor and has become the main stumbling block in realizing potential devices based on the ferroelectric materials as well as the development of related science. The knowledge of the physical natures of the pseudo-relaxor behavior and how to distinguish it from the true-relaxor behavior become the urgent scientific issues to be solved nowdays. Based on our previous research and starting with the key and adjustable factor — dielectric mismatch, the program aims at the following objectives in grain boundaries, electrode-sample contacts, thin film-substrate interfaces, and the intrinsic interfaces in strong interaction electronic systems: .1)systematically investigate the physical natures of the pseudo-relaxor behavior;.2)control and adjust the pseudo-relaxor behavior in terms of external fields (such as stress, electric, and magnetic fields) and element substitution;.3)establish a convenient and effective criterion for distinguishing the true from the pseudo-relaxor behavior; and .4) explore new physical effects associated with the interfacial polarization;..Interfacial-related phenona are currently hot issues in the fields of condensed mater physics and material sciences. The achievements of this project will expand the dielectric physics, especially the physics of the interfacial polarization, contribute to exploring and application of interface-related properties, and advance the development in science and technology. On the other hand, the investigations on the pseudo-relaxor behavior will add new contents to the “interfacial engineering”.

由界面极化产生的伪弛豫铁电行为由于与豫铁电体的介电行为相同，已严重阻碍了与铁电性关联的功能材料及相关科学和产业发展，其物理特征以及如何甄别真假弛豫铁电行为是当前急需解决的科学问题。本项目拟在前期工作的基础上，以晶界、电极-样品接触界面、薄膜-衬底界面，以及电子强相互作用体系中的内禀界面为研究对象，从介电失配这一关键可调因素入手，深入系统地研究伪弛豫铁电行为，力图揭示其物理特征；掌握伪弛豫铁电行为随外场（力场、电场、磁场等）变化的规律，并利用外场和元素掺杂来调控这种介电行为；探索一种简便有效的方法来区分真假弛豫铁电行为；积极探索与界面极化相关的其他物理效应。.界面现象是当前凝聚态物理和材料科学的研究热点，本项目的成功实施，有望极大地丰富电介质理论尤其是界面极化理论，为探索新的介电功能材料和发展新的多功能器件奠定基础和提供理论指导。同时，对伪弛豫铁电行为的研究将为“界面工程”添砖加瓦。

本项目从介电失配入手，对氧化物材料中的伪弛豫铁电行为进行了系统研究，研究结果表明该行为是由极化子弛豫和界面弛豫等两个源自氧空位的跳跃运动弛豫构成的，介电损耗角（tan）的行为是区分真假弛豫铁电行为最好的判据：对伪弛豫铁电行为，其介电损耗角的峰位随测量频率升高而向高温移动，表现出弛豫的特性，而对真弛豫铁电行为，其介电损耗角的峰位不随测量频率移动，表现出相变的特性。同时发现，伪弛豫铁电行伴随着优异的介电调谐性，该性能来源于界面极化和偶极极化的共同作用。此外，在多铁材料中，发现由磁有序导致的内禀界面，其极化行为具有记忆效应，这一效应归因于较弱磁场下较强的反铁磁关联，通过插入减弱磁场的中间过程, 最后再循环回到原有磁场, 能使观测到的记忆效应得到极大增强。在伪弛豫铁电行为的调控方面，发现直流电场可以显著影响伪弛豫铁电行为发生的温度，磁场可以调控多铁材料中伪弛豫铁电行为。项目成果丰富了电介质物理，尤其是界面极化的内容，为进一步探索新的介电功能材料提供了理论指导。