Correlation between microstructure and electrical conductivity in composite electrolytes containing Gd-doped ceria and Gd-doped barium cerate

Composite electrolytes with nominal compositions, Ce0.8Gd0.2O1.9 + xBaO (x = 0.2 and 0.3), have been synthesized through the citrate route. Formation of two phases, namely Gd-doped ceria and Gd-doped barium cerate, has been confirmed through XRD and SEM studies. The impedance spectra show three distinct semi-circles, all originating from the composite electrolytes. In the temperature range 175–350 °C, the activation energies for the conductivity values extracted from the high frequency and intermediate frequency parts of the impedance spectra remains the same, irrespective of compositional and micro-structural variation. On the other hand, the activation energies for the conductivity values associated with the low frequency impedance spectra show a significant change with micro-structural variation. Solid oxide fuel cells constructed using these composite electrolytes exhibit a higher open circuit voltage compared to those based on single phase 20 mol% Gd-doped ceria.