Fabrication of Bi0.95-xEr0.05MxO1.5-δ (M = Lu, Ho, and Gd) electrolyte for intermediate temperature solid oxide fuel cells

In this study, the samples of Lu2O3, Gd2O3, and Ho2O3 are firstly chosen as co-dopants with Er2O3 in order to stabilize δ phase Bi2O3 ceramics. The effects of co-dopants were investigated on phase stability and electrical conductivity of Bi0.95-xEr0.05MxO1.5-δ (M = Lu, Gd, and Ho) with x = 0.05 and 0.1 M ratio concentrations. The phase structure of samples was determined by X-ray diffraction method, the features of surface morphology are shown by scanning electron microscope, and the electrical conductivity is measured by AC impedance spectroscopy. All the samples have a face-centered cubic structure (fcc) at a lower sintering temperature (850 °C). The unit cell parameters are reduced due to the smaller dopant cations than Bi3+. The change of electrical conductivity in terms of the ionic radii, amount of doping, and temperature of the samples was investigated. The electrical conductivity increases with the radius of the doping ions. However, the increased amount of doping reduces conductivity. At the same time, the electrical conductivity of all the samples has increased with temperature. The best conductivity values are 0.489, 0.341, and 0.258 Scm−1 at 800, 700, and 600 °C, respectively for Bi0.90Er0.05Gd0.05O1.5. These values are significantly higher than the values found in the literature.