Mixed ionic and electronic conduction in YSZ-NiO composite

The electrical properties of yttria (8 mol %)-stabilized zirconia (YSZ)-nic kel oxide (NiO) composites were examined between 400 and 1000 degrees C. Th e temperature and oxygen partial-pressure dependence of conductivity and th e electromotive force measurement of the galvanic cells helped to determine the electronic contribution to total conduction in a wide composition rang e. Ion blocking electrodes were used to determine small electronic contribu tion to the total current flow. With increasing the NiO content, a transiti on from ionic to electronic conduction was observed. Mixed conduction was o bserved for the composition between 40 and 80 mol % Of NiO at 800 similar t o 1000 degrees C. A shrinking mixed conduction region with decreasing tempe rature was shown for the Li-doped NiO addition. The activation energy and t he oxygen partial-pressure dependence of conductivity also reflected connec tivity and thus changes in the conduction mechanism of the composites. In t he ionic conduction region, the electronic current increased by nearly 50 t imes with the addition of NiO without interconnection by NiO grains. (C) 19 99 The Electrochemical Society. S0013-4651(98)05-043-5. All rights reserved .