Understanding the sintering temperature effect on oxygen ion conductivity in doped ceria electrolytes

Achieving a high electrical conductivity with a low sintering temperature is an important goal in the development of solid oxide fuel cell electrolytes. Herein, nanoscale doped ceria materials Ce_0.9Gd_0.1-xBi_xO_1.95 (x = 0 and 0.02–0.05) were prepared by the coprecipitation method for this purpose. Impedance spectroscopy analyses performed at 250 and 400 °C was employed to calculate sample’s electrical conductivity, which were sintered at various temperatures. The electrical conductivity was observed to decrease with increasing sintering temperature. The optimal sintering temperature of Ce_0.9Gd_0.08Bi_0.02O_1.95 and Ce_0.9Gd_0.1O_1.95 was 1300 and 1400 °C, respectively. The material Ce_0.9Gd_0.08Bi_0.02O_1.95 presented an electrical conductivity of 8.1 × 10⁻⁴ S cm⁻¹ at 400 °C, i.e., four times that of GDC (x = 0) sintered at 1400 °C (2.0 × 10⁻⁴ S cm⁻¹ at 400 °C). It is believed that these effects results from the Schottky barrier height and oxygen vacancy concentration within the space charge layer changing with sintering temperature. This oxygen vacancy depletion in the space charge layer is also believed to account for the oversintering effect.