Anisotropic Memristive Switching in NbOCl ₂ Enabled by Directional Oxygen Ion Migration

ABSTRACT Directional ion transport in anisotropic two‐dimensional (2D) materials provides a powerful yet underexplored pathway for engineering memristive functionalities. Here, we demonstrate strongly orientation‐dependent memristive switching in layered NbOCl ₂ lateral devices, where resistive switching occurs exclusively along the in‐plane c‐axis, while devices aligned along the b‐axis exhibit no hysteresis. The c‐axis devices show forming‐free volatile memristive behavior with a stable on/off ratio and cycle‐to‐cycle reproducibility. Combined experiments and first‐principles calculations reveal that the anisotropic switching originates from direction‐dependent oxygen‐ion migration and vacancy propagation, which modulate the Schottky barrier at the Pd/NbOCl ₂ interface. The resulting ion‐driven barrier modulation enables key synaptic functions, including excitatory postsynaptic current, paired‐pulse facilitation, spike‐rate‐dependent plasticity, and spike‐amplitude‐dependent plasticity, demonstrating short‐term synaptic plasticity. Leveraging the intrinsic nonlinear and self‐relaxation dynamics, the NbOCl ₂ memristor is further implemented as a physical reservoir, achieving 94.3% accuracy in handwritten digit recognition using the MNIST dataset. These results reveal NbOCl ₂ as a promising anisotropic memristive material and highlight directional ion migration in 2D systems as a versatile strategy for neuromorphic hardware and reservoir computing applications.