Zhang Le, Zhao Luo, He Liqiang, Wang Dong, Sun Yunlong, Wang Danyang, Lou Xiaojie, Zhang Lixue, Carpenter Michael A
School of Power and Energy, Northwestern Polytechnical University, Xi'an 710129, China.
School of Materials Science and Engineering, The University of New South Wales, Sydney, NSW 2052, Australia.
ACS Appl Mater Interfaces. 2022 Jan 12;14(1):1434-1442. doi: 10.1021/acsami.1c19856. Epub 2022 Jan 3.
The morphotropic phase boundary (MPB) in lead-free ferroelectrics, starting from a quadruple point (QP), often displays large piezoelectric responses due to the flattened free-energy profiles. In this work, we found that the QP composition rendering most flattened energy profiles could also exhibit abnormally low piezoelectric constants in Hf-doped BaTiO. Such an anomaly in the strength of piezoelectricity can be ascribed to the progressive influence of additional strain heterogeneity induced by the substitution of Hf for Ti in BaTiO, which was overlooked previously. An intermediate level of strain heterogeneity can form an invisible ferroelectric crossover consisting of both micro- and nanodomains, resulting in a large elastic softening and high piezoelectricity. With a further increase in the level of strain heterogeneity, the extinction of regular ferroelectric domain structures and pinned polar dynamics resulted in the feeble piezoelectric outputs near the QP composition. Impressively, a giant of ∼610 pC/N has been accordingly obtained through employing a ferroelectric crossover at off-QP composition in Zr-doped BaTiO, further underpinning the critical role of uncovered ferroelectric crossover on piezoelectricity along MPB. This work offers another degree of freedom in the design of high-performance eco-friendly piezoelectric ceramics.
无铅铁电体中的形态转变相界（MPB），从四重简并点（QP）出发，由于自由能分布变平，常常表现出较大的压电响应。在这项工作中，我们发现，在掺铪的钛酸钡中，使能量分布最平坦的QP成分也可能表现出异常低的压电常数。这种压电性强度的异常可归因于钡钛矿中铪取代钛所引起的额外应变不均匀性的渐进影响，这一点此前被忽视了。中等程度的应变不均匀性可以形成由微米和纳米畴组成的不可见铁电转变，导致大的弹性软化和高压电性。随着应变不均匀性程度的进一步增加，规则铁电畴结构的消失和固定的极化动力学导致QP成分附近的压电输出微弱。令人印象深刻的是，通过在掺锆的钛酸钡中采用非QP成分处的铁电转变，相应地获得了约610 pC/N的巨大压电常数，进一步证实了未被发现的铁电转变对沿MPB的压电性的关键作用。这项工作为高性能环保压电陶瓷的设计提供了另一个自由度。
