Yttria [12 mole percent (m/o)] stabilized zirconia with 5 to 10 m/o titania (YZTi) exhibits oxygen-ion and n-type conductivity under reducing atmospheres at elevated temperatures. Electron paramagnetic resonance (EPR) measurements reveal that the Ti3+ concentration of YZTi increases with increasing temperature, increasing TiO2 content, and decreasing oxygen pressures below 10(-10) arm at 830 degrees C. Impedance measurements show that the total electrical (oxygen-ion plus n-type) conductivity of YZTi having 10 m/o TiO2 follows the same behavior and increases at oxygen pressures below 10(-22) and 10(-15) atm at 573 and 838 degrees C, respectively. The EPR and impedance results support an electron hopping mechanism between the 3(+) and 4(+) oxidation states of titanium. Modeling of the impedance data verifies that the n-type conductivity ty occurs in the YZTi lattice and is not restricted to the grain boundaries. A percolation model shows that electron hopping can occur in YZTi when titanium ions occupy as few as 3 to 4% of the cation sites.