Negative differential resistance and hysteresis in Au/MoO_3-δ/Au devices

Metal/oxide/metal thin devices may exhibit hysteresis and negative differential resistance (NDR) under time-varying voltage at low temperatures that strongly depend on the frequency of the applied voltage. Herein, we demonstrated and analyzed this in Au/MoO_3-δ/Au devices, tested at 55-80 °C. Reduced MoO_3-δ is a mixed ionic-electronic conductor (MIEC) that conducts electrons and oxygen vacancies. Hysteresis and NDR disappear at high scan rates of the applied voltage when the ion motion is practically frozen and at low scan rates when the response to voltage cycles is quasi-static. Contrary to cyclic voltammetry in electrochemistry, peaks that appear and end with NDR are not because of a redox reaction but a result of the dynamics of the ionic motion. A low rate of exchange of oxygen with the ambient is detected during prolonged measurements. The anodic reaction is found to be faster than the cathodic reaction, and the oxide is reduced under (anti) symmetric voltage cycles. Upon fitting a theory previously reported by our group, the electron mobility and activation energy, oxygen vacancy mobility and activation energy, as well as oxygen exchange current density of the electrodes, of the device were obtained at relatively low temperatures.