Effect of a DC bias on the conductivity of gadolinia doped ceria thin films

Abstract

This paper studies the phenomenon of mixed ionic and electronic conductivity in magnetron sputtered gadolinia doped ceria thin films under the effect of an applied DC bias. Electrochemical impedance spectroscopy was used to measure the change in impedance under an alternating voltage of 300 mV, at temperatures between 25 °C and 150 °C and applied biases of ∼4–20 kV/mm, which are much higher than any prior study. The application of a DC bias produces a reversible decrease in both the grain and grain boundary resistances for GDC, and the films exhibit bias-induced mixed ionic and electronic conductivity. Additional features become visible in the Nyquist plots, indicating possible novel mechanisms in response to bias. Particularly interesting is the appearance of inductive loops in the low frequency regime, at very high bias values, rarely seen for such materials. Here this novel behavior was analyzed by fitting the data using equivalent circuits to understand the underlying mechanisms at play. Through this work, it is established that the change in behavior is attributed to electronic conduction through grain boundaries along the direction of the applied field.