Operando Observation of Electrically Triggered Phase Transition in Thin Cu 2 S Crystal

Cu S has been identified as a functional material of memristors with multilevel resistance switching. However, as the migration of Cu ions under the electric field is tangled with defect evolution and phase transition, the electroresistance mechanism of Cu S remains largely unclear. Here, the electrically triggered phase transition was studied by transmission electron microscopy. It is found that the γ(L)-Cu S phase is transformed into β-Cu S accompanied by the change in resistance, when a voltage lower than 1 V is applied at room temperature. The electrically triggered phase transition is also observed at -150 °C. Precipitation of metal Cu nanoparticles is observed when the applied voltage is further increased after the complete formation of β-Cu S. These findings indicate that Cu S can achieve fast and controllable phase switching through electrical tuning when the energy consumption is appropriately controlled, offering the potential for low-power electronic devices such as memory and sensors.