Mixed ionic and electronic conduction in YSZ-NiO composite

The electrical properties of yttria (8 mol %)-stabilized zirconia (YSZ)-nickel oxide (NiO) composites were examined between 400 and 1000 degrees C. The temperature and oxygen partial-pressure dependence of conductivity and the electromotive force measurement of the galvanic cells helped to determine the electronic contribution to total conduction in a wide composition range. Ion blocking electrodes were used to determine small electronic contribution to the total current flow. With increasing the NiO content, a transition from ionic to electronic conduction was observed. Mixed conduction was observed for the composition between 40 and 80 mol % Of NiO at 800 similar to 1000 degrees C. A shrinking mixed conduction region with decreasing temperature was shown for the Li-doped NiO addition. The activation energy and the oxygen partial-pressure dependence of conductivity also reflected connectivity and thus changes in the conduction mechanism of the composites. In the ionic conduction region, the electronic current increased by nearly 50 times with the addition of NiO without interconnection by NiO grains. (C) 1999 The Electrochemical Society. S0013-4651(98)05-043-5. All rights reserved.