A study of gadolinia-doped ceria electrolyte by electrochemical impedance spectroscopy

Samples of Gd2O3-doped CeO2 (GDC) were fabricated by sintering of powder compacts. Impedance spectra were measured from 400 °C to 675 °C in air by electrochemical impedance spectroscopy (EIS). Above ∼500 °C, high frequency arc was not semicircular but could be fitted with a constant phase element (CPE). Above ∼625 °C, high frequency arc could not be resolved due to a significant contribution from the inductive load. The impedance spectra were described using a simple equivalent circuit which included the leads/instrument impedance. The leads/instrument impedance was measured over a range of frequencies and temperatures. The high frequency part of the impedance after subtracting leads/instrument impedance could be resolved even at the highest measurement temperature and was described by a semicircle representative of transport across grain boundaries. From these measurements, grain and grain boundary resistivities were determined. The corresponding activation energies were 0.69 eV and 1.11 eV, respectively. The grain boundary capacitance was nearly independent of temperature. The present results show that grain boundary effects can be described by a resistor and a capacitor. Relevant equivalent circuit parameters were obtained from intercepts, maxima and minima in impedance diagrams.