Alternate current nonequilibrium molecular dynamics simulations of yttria-stabilized zirconia

An alternating current nonequilibrium molecular dynamics (AC-NEMD) simulation technique is applied to study the ionic conduction behavior of 8 mol % yttria-stabilized zirconia (YSZ). A maximum conductivity is observed at a frequency of 3 x 10(13) Hz when the current response is in phase with the applied field. The current response lags the applied field at lower frequencies but leads the applied field at higher frequencies, in both cases having lower conductivity than when current response is in phase. Represented by a Cole-Cole plot of complex admittance representation, the AC-NEMD data indicate a resistance-capacitance (RC) circuit behavior at low frequency and resistance-inductance (RL) circuit behavior at high frequency. The frequency dependent ionic conductivity may be correlated to the length scale and time scale of oxygen transport between vacancy sites. In the AC-NEMD, the generated ohmic heat is effectively removed, and a constant temperature is maintained by an Anderson thermostat. Separate NEMD simulations performed with a Nose-Hoover thermostat give mostly identical results, within statistical error bars.