Anomalous toughening in nanoscale ferroelectrics with polarization vortices
Anomalous toughening in nanoscale ferroelectrics with polarization vortices
复制标题
极化涡旋纳米级铁电体的异常增韧
DOI：
10.1016/j.actamat.2014.12.056
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发表时间：
2015-04-15
期刊：
影响因子：
9.4
通讯作者：
Kitamura, Takayuki
中科院分区：
文献类型：
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作者：
Van Lich, Le;Shimada, Takahiro;Kitamura, Takayuki
使用基于 Ginzburg Landau 理论的最先进的实空间相场模型研究了纳米级铁电体裂纹的异常机械行为，其中自发极化形成闭合通量涡流。由于裂纹尖端附近的剧烈应力释放，纳米级铁电体表现出异常大的增韧效应，其应力强度比宏观材料中观察到的应力强度几乎大一个数量级。这种异常增韧归因于纳米级铁电体中极化涡流的异常切换行为，它不再像宏观铁电体中那样局限于裂纹尖端附近，而是通过涡流的分裂和倍增扩展到整个结构。我们进一步证明，这种局部到全局的切换本质上是由铁电极化和机械应变之间的强交叉耦合引起的，机械应变不仅集中在裂纹尖端附近，而且由于分布不均匀而集中在每个极化涡流中。我们的发现为纳米级极化涡旋提供了新的见解，并提出了一种全新的策略，通过设计极化涡旋的微观结构来定制和提高铁电材料的断裂韧性。 (c) 2015 Acta Materialia Inc. 由 Elsevier Ltd 出版。保留所有权利。
Unusual mechanical behavior of cracks in nanoscale ferroelectrics, where spontaneous polarization characteristically forms closed-flux vortices, is investigated using state-of-the-art real-space phase-field modeling based on the Ginzburg Landau theory. An anomalously large toughening effect is revealed in nanoscale ferroelectrics due to drastic stress release near the crack tip, which is almost one order of magnitude larger in stress intensity than that observed in macroscale materials. Such anomalous toughening is attributed to an unusual switching behavior of the polarization vortices in nanoscale ferroelectrics, which is no longer localized near the crack tip as in macroscale ferroelectrics, but expands to the entire structure through the splitting and multiplication of vortices. We further demonstrate that this local-to-global switching is intrinsically induced by strong cross-coupling between the ferroelectric polarization and mechanical strain that concentrates to the electro-elastic energy, not only in the vicinity of crack tip, but also to each polarization vortex due to its inhomogeneous distribution. Our finding provides a novel insight into nanoscale polarization vortices and leads to an entirely new strategy for the tailoring and improvement of fracture toughness in ferroelectric materials by engineering the microstructure of polarization vortices. (c) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.