ELECTRICAL-CONDUCTIVITY AND THERMAL-EXPANSION OF CERIA-DOPED WITH PR, NB AND SN

The effect of Pr, Nb and Sn substitution on the electrical conductivity, thermal expansion and the structure of the phases formed was investigated in a series of samples based on ceria solid solutions. X-Ray diffraction (XRD) analysis was performed in order to study the phase content and to measure the cell lattice parameters. Electrical conductivity was measured in air by means of the four-point DC technique, within the temperature range 400-1000 degrees C. Also, thermal expansion coefficient measurements were carried out using the dilatometer technique. The results show that doping of ceria with 8-10 mol% praseodimia increases the electrical conductivity, while the addition of Nb2O5 leads to the formation of a second, monoclinic, phases which decreases the conductivity. The thermal expansion coefficient in Pr-doped ceria is 8 x 10(-6)/K at temperatures lower than 500 degrees C, then it increases to 10-11 x 10(-6)/K at 900 degrees C. Doping with Nb2O5 eliminates the increase of thermal expansion at high temperatures. Sn was found to be a possible substitute for Ce in ceria solid solutions.