Wang Xuechen, Ren Yangyang, Wu Menghao
School of Physics and School of Chemistry, Institute of Theoretical Chemistry, Huazhong University of Science and Technology, Wuhan430074, China.
College of Physics and Electronic Science, Hubei Normal University, Huangshi435002, China.
J Phys Chem Lett. 2022 Oct 20;13(41):9552-9557. doi: 10.1021/acs.jpclett.2c02601. Epub 2022 Oct 6.
Ferroelectricity is generally a displacive phenomenon within a unit cell in which ions are placed asymmetrically. In ionic conductors, ions can also be electrically displaced but by much longer distances. They are mostly nonpolar with symmetrical lattices due to the nondirectional character of ionic bondings. Here we propose that the combination of two such displacive modes may give rise to unconventional ferroelectricity with quantized polarizations, where even one local vacancy may induce giant polarization in ubiquitous ionic conductors. Such systems should be insulating with ion vacancies inclined to aggregate at one side. Our high-throughput screening combined with calculations provided 35 candidates, from which we select KSnS and NaSnS to show the existence of such long ion displacement ferroelectricity with a change in integer quantum number in polarizations during switching. The polarizations can be unprecedentedly large with a moderate density of ion vacancies that can be experimentally achieved via ion deintercalation.
铁电性通常是一种晶胞内的位移现象，其中离子呈不对称排列。在离子导体中，离子也会发生电位移，但距离要长得多。由于离子键的无方向性，它们大多具有对称晶格，是非极性的。在此我们提出，两种这样的位移模式相结合可能会产生具有量子化极化的非常规铁电性，在普遍存在的离子导体中，即使一个局部空位也可能诱导出巨大极化。这样的系统应该是绝缘的，离子空位倾向于聚集在一侧。我们的高通量筛选结合计算提供了35个候选材料，从中我们选择了KSnS和NaSnS来证明这种长离子位移铁电性的存在，其在切换过程中极化的整数量子数会发生变化。通过离子脱嵌在实验上可以实现适度的离子空位密度，此时极化可能会前所未有的大。
