Ionic conductivity of gadolinium-doped barium cerate perovskites

Abstract

Gadolinium-doped barium cerate perovskites of formula BaCe 1-x Gd x O 3- x 2 have been prepared and studied by X-ray powder diffraction, impedance spectroscopy, concentration cell and Faradaic oxygen transport cell techniques. The highest conductivity was observed for x=0.15, the maximum doping level for which single phase products were obtained. At temperatures of 500°C and below, the compounds exhibited mainly ionic conductivity with activation energies of 0.45 to 0.55 eV. The ionic transport number of BaCe 1-x Gd x O 3- x 2 (x=0.10) was studied by measurement of the total conductivity versus P O2 and the EMF of oxygen and hydrogen concentration cells. At high temperature and at high oxygen partial pressure this compound is a mixed ionic and p-type electronic conductor while at low oxygen partial pressure it is a pure ionic conductor. The Faradaic transport of oxygen was demonstrated, indicating that ionic conduction occurs predominantly by migration of oxide ions. The ionic component of the conductivity was determined as 11 mS cm -1 at 600°C and 16 mS cm -1 at 800°C. The value at 600°C is the highest measured for any perovskite oxide, including BaCeO 3:Y and BaCeO 3:Nd, and is about 60% of that reported for ceria-gadolinia solid electrolytes. However, unlike tha latter, barium cerate-based solid electrolytes are stable to reduction by hydrogen at high temperature and, thus, are good candidates for solid oxide fuel cell applications.