Polarization in ferroelectrics can be switched in the direction of an applied electric field by dipole reorientation, enabling numerous applications and fundamental phenomena. Here, we demonstrate that, in the van der Waals (vdW) layered ferrielectric ${\mathrm{Cu}\mathrm{In}\mathrm{P}}_2{\mathrm{S}}_6$, a unique mechanism exists where polarization aligns against the direction of the applied electric field, seemingly in violation of the fundamental properties of a dipolar solid. The mechanism is the result of the electric field driving the $\mathrm{Cu}$ atoms unidirectionally across the vdW gaps, which is distinctively different from dipole reorientation. The crossing of $\mathrm{Cu}$ atoms is the fundamental process of ionic conductivity, yet it is compatible with the existence of polarization. These phenomena are confirmed by nanoscale imaging and spectroscopy of ferroelectric capacitors, coupled with dynamic density-functional-theory simulations. The symbiotic relationship of ferroelectric and ionic phenomena enables alternative approaches to control polarization and necessitates a change in perspective on nucleation, domain-wall dynamics, and other ferroelectric and electromechanical characteristics in material systems where ionic and ferroelectric phenomena manifest.

中文翻译：

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范德华铁电体中电场的极化取向

铁电体中的极化可以通过偶极子重新定向在施加的电场方向上切换，从而实现众多应用和基本现象。在这里，我们证明，在范德华（vdW）层状铁电体中${铜在\mathrm{P}}_2{\mathrm{小号}}_6$，存在一种独特的机制，其中极化与施加的电场方向对准，这似乎违反了偶极固体的基本特性。该机制是电场驱动电磁场的结果。$铜$原子单向穿过vdW间隙，这与偶极子重新定向是明显不同的。穿越$铜$原子是离子电导率的基本过程，但它与极化的存在兼容。这些现象已通过铁电电容器的纳米级成像和光谱学以及动态密度泛函理论仿真得到了证实。铁电和离子现象的共生关系使控制极化的替代方法成为可能，并且在离子和铁电现象表现出来的材料系统中，必须改变成核，畴壁动力学以及其他铁电和机电特性的观点。