Electronic conduction mechanism in yttria-stabilized zirconia-titania under reducing atmospheres

Yttria stabilised zirconia with 5 to 10 mol% titania (YZTi) exhibits oxygen-ion and n-type conductivity under reducing atmospheres at elevated temperatures. The Ti3+ concentration of YZTi increases with increasing temperature, increasing TiO2 content, and decreasing oxygen pressures below 10 exp(-10) atm at 830 C. The total electrical conductivity of YZTi having 10 mol% TiO2 follows the same behaviour and increases at oxygen pressures below 10 exp(-22) and 10 exp(-15) atm at 573 and 838 C, respectively. An electron hopping mechanism occurs between the 3+ and 4+ oxidation states of titanium. Modelling of impedance data verifies that the n-type conductivity 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. 32 refs.