N-TYPE CONDUCTIVITY IN GADOLINIA-DOPED CERIA

The ionic and n-type conductivities of ceria-based electrolytes doped with gadolinium (10 and 20 cation %) or gadolinium and praseodymium (2 % Pr and 18% Gd) were studied by impedance spectroscopy in air, betwee n 573 and 1273 K, and by constant frequency (10 kHz) conductivity meas urements as a function of the oxygen partial pressure (p(o2)) between about 10(-20) atm and air in the temperature range 1073 to 1273 K. Ion blocking measurements were also performed between 1073 and 1273 K wit h air at the reversible electrode. From data obtained with different e xperimental techniques it was concluded that estimates for the electro nic conductivity of all compositions were consistent and that all mate rials behaved in a rather similar manner. Estimated n-type conductivit ies suggest that Pr-doped materials have a slightly lower electronic c onductivity and a larger electrolytic (and ionic) domain, but overall differences are quite small. The model behavior used in analyzing expe rimental results is discussed based on the existing knowledge of the d efect chemistry of ceria-based electrolytes, and a range of working co nditions is identified where the ionic conductivity can be assumed con stant and the electronic conductivity proportional to p(o2)(-1/4).