Nanoscale Mapping of Cu‐Ion Transport in van der Waals Layered CuCrP2S6

Ionic conduction of metal thiophosphates (MTPs) is attracting growing attention for promising applications in electrochemical storage and tunable physical properties. Especially, metal‐ion migration in copper thiophosphate has been identified as a key factor for the control of their microstructure and phase transition. However, direct evidence for the coupling between Cu‐ion motions and the crystal lattice has been elusive at the nanometer scale. Here, the room temperature diffusion kinetics of Cu ions in layered CuCrP2S6 (CCPS) is demonstrated. A tip‐enhanced electric field based on scanning probe microscopy (SPM) has been used as the driving force for Cu‐ion motions through van der Waals gaps. The strong coupling between Cu‐ion concentration and crystal lattice and the resulting serial structural transitions have been probed directly by the comprehensive utilization of spatially resolved Raman spectra, cross‐section energy dispersion spectrum (EDS), and high‐resolution transmission electron microscopy (HR‐TEM). This knowledge improves the understanding of the effect of intrinsic Cu‐ion migration on the structure transformation in layered van der Waals materials and provides feedback to the nanoscale mechanisms of nanometer devices based on iontronics. The intrinsic ionic conductivity and the strong coupling between Cu‐ion concentration and crystal lattice in layered CuCrP2S6 have been probed directly at a resolution of nanometers.