铁电材料的时效效应及超大可回复电致应变-中国材料进展

文章信息/Info

Title:: Aging phenomenon in ferroelectrics and the related large recoverable electro-strain effect

Author(s):: ZHANG Lixue; REN Xiaobing; State Key Laboratory for Mechanical Behavior of Materials, School of Materials Science and Engineering, and Frontier institute for Science and Technology, Xi’an Jiaotong University

摘要:: 铁电材料的性能在铁电相变后会产生随时间变化的“时效现象”。铁电时效现象对铁电材料的应用产生重要影响，导致其性能可靠性下降。铁电时效与可动点缺陷（如氧空位）的扩散密切相关，但其微观机理一直未被阐释清楚。核心问题是无法理解铁电相变为什么会驱动点缺陷扩散。作者基于其所提出的铁电晶体中的点缺陷短程有序对称性原理（X Ren, Nature Materials, 3: 91, 2004），指出：铁电相变后，晶体对称性发生改变，点缺陷短程有序对称性受控于晶体对称性而发生改变的这一原理驱动了点缺陷的扩散。进一步，通过时效调控晶体点缺陷的对称性，产生电场下可逆的电畴翻转，在钛酸钡铁电材料中发现了40倍于传统电致应变的巨大可回复电致应变效应。该结果为开发大电致应变材料提供了途径。此外，通过原位偏光显微镜观察验证了可逆畴翻转过程，为可回复大电致应变提供了直接的介观证据。并对电子顺磁共振谱线进行分析，证明了点缺陷具有与晶体对称性一致的轴向对称性。同时指出，利用晶体对称性与点缺陷对称性发生改变时的时间差，可获得多尺度的新奇效应。

Abstract:: Ferroelectric aging usually refers to a gradual changing of properties with time. It lowers the reliability of ferroelectric devices and is usually undesirable for ferroelectrics. The occurrence of aging is closely related with the diffusion of mobile defects in ferroelectrics, yet a microscopic mechanism remains unclear. In the present paper, the authors pointed out that aging is microscopically driven by a symmetry conforming force of defect symmetry to crystal symmetry, based on the proposed symmetry-conforming short-range-order (SC-SRO) principle of point defects in ferroelectric crystals (X Ren, Nature Materials, 3: 91, 2004). More importantly, a giant recoverable electro-strain in aged BaTiO3-based ferroelectrics was obtained via a defect mediated reversible domain switching, which is 40 times larger than the traditional electro-strain effect. The results provide a promising way for designating high electro-strain materials. Besides, direct evidence for the reversible domain switching process behind the large recoverable electro-strain was given by an in situ polarizing microscope observation. The symmetry relation between point defects and crystals was also discussed in light of the SC-SRO principle and electron paramagnetic resonance spectroscopy. Multi-scale novel effects are expected from the time-lag between the symmetry changing of crystals and point defects.