Electronic Conductivity in Yttria-Stabilized Zirconia under a Small dc Bias

Yttria-stabilized zirconia, YSZ, is the oxide ion conducting electrolyte of choice in many solid oxide fuel cells, because of its resistance to reduction at the fuel electrode. Here, we demonstrate that electronic conduction is introduced into YSZ under the action of a small dc bias at high temperatures in air. A reversible decrease in sample grain and grain boundary resistances occurs with increasing bias in the range 1-15 V and the Warburg impedance at the sample-electrode-air interface collapses. Similar conductivity changes are seen with acceptor-doped dielectrics and are attributed to the ionization of underbonded oxide ions in the crystal structure, with O- ions acting as the location of the holes and the source of p-type conduction; the ionized electrons are trapped by changes to the equilibria among oxygen species at the sample surface. A similar mechanism may explain the onset of electronic conductivity in YSZ.