Electrical Conduction in Nb2 O 5 ‐ Doped Cerium Dioxide

Electrical conductivity of the sintered Nb 2 O 5 ‐ doped CeO 2 specimens was measured between 800° and 1329°C in the p O 2 range 10 −19 –1 atm. A polarization technique was used to determine the predominant electrical conduction mode in these specimens. Thermogravimetric analysis was done to measure the weight loss in selected specimens. The solid solubility limit of Nb 2 O 5 in CeO 2 is between 0.60 and 0.80 m/o, and it does not vary significantly with temperature or p O 2 . The Nb 2 O 5 ‐ doped CeO 2 is an n‐type semiconductor. At high p O 2 , Nb 5+ ions are incorporated in CeO 2 by both possible charge‐compensating mechanisms, viz., ( i ) reduction of some Ce 4+ to Ce 3+ and ( ii ) formation of oxygen interstitials. At low p O 2 , the first mechanism predominates. Doping with Nb 2 O 5 significantly increases the electrical conductivity of CeO 2 in the high p O 2 range. This extrinsic electronic conductivity, arising from mechanism ( i ), predominates over the intrinsic conductivity at high p O 2 (10 −4 –1 atm) and lower temperatures (800°–1029°C) giving p O 2 ‐ independent total conductivity at a constant temperature. At lower p O 2 or higher temperature, the intrinsic defects of CeO 2 − x increasingly affect the conductivity.