Kinetic Monte Carlo simulations of oxygen vacancy diffusion in a solid electrolyte: Computing the electrical impedance using the fluctuation–dissipation theorem

We present a new method for computing the electrical impedance of solid oxide electrolyte from kinetic Monte Carlo simulations of oxygen vacancy diffusion. The impedance values at all frequencies are obtained from a single equilibrium simulation based on the fluctuation–dissipation theorem, leading to a significant gain of efficiency over existing methods.This allows us to systematically examine the effect of dopant concentration. Increasing dopant concentration is found to decrease the infinite-frequency impedance, which is attributed to the increasing density of oxygen vacancies. The difference between the impedance values at zero- and infinite-frequency, on the other hand, shows the opposite trend, and is linked to dopant–vacancy interactions. Hence the two competing mechanisms, previously proposed to explain the existence of an optimal doping concentration, are separately quantified.Our model also predicts a significant effect of the arrangement of dopant cations on the electrolyte conductivity.