Experimental demonstration of hybrid improper ferroelectricity and the presence of abundant charged walls in (Ca, Sr)3Ti2O7 crystals
Experimental demonstration of hybrid improper ferroelectricity and the presence of abundant charged walls in (Ca, Sr)3Ti2O7 crystals
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DOI：
10.1038/nmat4168
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发表时间：
2015-04-01
期刊：
影响因子：
41.2
通讯作者：
Cheong, Sang-Wook
中科院分区：
文献类型：
--
作者：
Oh, Yoon Seok;Luo, Xuan;Cheong, Sang-Wook
在新功能铁电材料成功的第一性原理预测的基础上，实验上发现了一系列新的铁电体。利用两种八面体旋转的三线性耦合，理论上预测了有序钙钛矿和Ruddlesden-Popper化合物（Ca_3Ti_2O_7，Ca_3Mn_2O_7和（Ca/Sr/Ba）（3）（Sn/Zr/Ge）（2）O-7）的杂化反常铁电性。然而，这些化合物的铁电性从未得到实验证实，甚至它们的极性也一直存在争议。在这里，我们提供了第一个实验演示的室温下可切换的极化体晶体的Ca 3 Ti 2 O 7，以及Sr掺杂的Ca 3 Ti 2 O 7。此外，（Ca，Sr）（3）Ti 2 O 7被发现表现出有趣的铁电畴结构的正交孪晶和（可切换）平面极化。平面畴结构伴随着丰富的带电畴壁与导电的头对头和绝缘的尾对尾的配置，表现出两个数量级的导电差异。这些发现不仅为Ruddlesden-Popper化合物的新的稳定铁电体，而且为平面极化形成的弯曲导电畴壁提供了新的研究机会。
On the basis of successful first-principles predictions of new functional ferroelectric materials, a number of new ferroelectrics have been experimentally discovered. Using trilinear coupling of two types of octahedron rotation, hybrid improper ferroelectricity has been theoretically predicted in ordered perovskites and the Ruddlesden-Popper compounds (Ca3Ti2O7, Ca3Mn2O7 and (Ca/Sr/Ba)(3)(Sn/Zr/Ge)(2)O-7). However, the ferroelectricity of these compounds has never been experimentally confirmed and even their polar nature has been under debate. Here we provide the first experimental demonstration of room-temperature switchable polarization in bulk crystals of Ca3Ti2O7, as well as Sr-doped Ca3Ti2O7. Furthermore, (Ca, Sr)(3)Ti2O7 is found to exhibit an intriguing ferroelectric domain structure resulting from orthorhombic twins and (switchable) planar polarization. The planar domain structure accompanies abundant charged domain walls with conducting head-to-head and insulating tail-to-tail configurations, which exhibit a conduction difference of two orders of magnitude. These discoveries provide new research opportunities, not only for new stable ferroelectrics of Ruddlesden- Popper compounds, but also for meandering conducting domain walls formed by planar polarization.