Anomalous Elastic Evolution Induced by Copper Hopping in van der Waals Ferroelectric CuInP2S6

Abstract Van der Waals (vdW) ferroelectric CuInP2S6 (CIPS) has great potential in post‐Moore's law electronics owing to their advantages of weak interlayer interaction, stable surface with free dangling bonds, and robust switchable spontaneous polarization. The flexoelectric effect is demonstrated as an alternative switching method for the design of ferroelectric domains in layered vdW CIPS. However, the investigation of the correlation between the polarization and elastic properties remains indistinct. Here, an elastic evolution is explored experimentally and theoretically in layered vdW CIPS with temperature, of which Young's modulus (EYoung) is determined by analyzing the force‐indentation responses of vdW ferroelectric CIPS. Interestingly, an anomalous leap in EYoung of CIPS from 35 to 65 GPa occurs when the temperature rises across the Curie temperature TC of ≈315 K. Deep potential molecular dynamic (DPMD) simulations identify that this abnormal behavior can be attributed to temperature‐dependent change of copper distribution and the local copper dynamic hopping, intertwined with the order‐disorder ferroelectric phase transition, which is quite different from the typical decrease of EYoung in the lattice constant due to temperature increasing. The exploration provides an important reference for the analysis of coupled mechanical properties and ferroelectricity in CIPS and its applications in flexible electronics.