Interlayer stacking order has recently emerged as a unique degree of freedom to control crystal symmetry and physical properties in two-dimensional van der Waals (vdW) materials and heterostructures. By tuning the layer stacking pattern, symmetry-breaking and electric polarization can be created in otherwise non-polar crystals, whose polarization reversal depends on the interlayer sliding motion. Herein, we demonstrate that in a vdW layered ferroelectric, its existing polarization is closely coupled to the interlayer sliding driven by hydrostatic pressure. Through combined structural, electrical, vibrational characterizations, and theoretical calculations, we clearly map out the structural evolution of CuInP2S6 under pressure. A tendency toward a high polarization state is observed in the low-pressure region, followed by an interlayer-sliding-mediated phase transition from a monoclinic to a trigonal phase. Along the transformation pathway, the displacive-instable Cu ion serves as a pivot point that regulates the interlayer interaction in response to external pressure. The rich phase diagram of CuInP2S6, which is enabled by stacking orders, sheds light on the physics of vdW ferroelectricity and opens an alternative route to tailoring long-range order in vdW layered crystals.

中文翻译：

---

压力下 CuInP2S6 中滑动介导的铁电相变

最近，层间堆叠顺序已成为控制二维范德华（vdW）材料和异质结构中晶体对称性和物理性质的独特自由度。通过调整层堆叠模式，可以在其他非极性晶体中产生对称性破坏和电极化，其极化反转取决于层间滑动运动。在此，我们证明了在 vdW 层状铁电体中，其现有的极化与静水压力驱动的层间滑动紧密耦合。通过结合结构、电学、振动表征和理论计算，我们清楚地绘制出 CuInP2S6 在压力下的结构演化。在低压区域观察到高偏振态的趋势，随后是层间滑动介导的从单斜相到三角相的相变。沿着转变路径，位移不稳定的铜离子充当枢轴点，调节层间相互作用以响应外部压力。 CuInP2S6 的丰富相图是通过堆叠顺序实现的，它揭示了 vdW 铁电性的物理原理，并开辟了一条在 vdW 层状晶体中定制长程有序的替代途径。