Electrical Characterization of Highly Titania Doped YSZ

The defect fluorite region of the ternary system ZrO(2)-Y(2)O(3)-TiO(2) encompasses compositions which offer both, good electronic and oxygen ion conductivity which enable good catalytic activity for the direct oxidation of methane in a solid oxide fuel cell (SOFC). The electrical properties of compositions Y(x)Ti(y)Zr(1-(x+y))O(2-x/2) (with x = 0.15, 0.2, 0.25 and y = 0.15, 0.18) were characterised in order to find the composition with highest ionic and electronic conductivity. High titanium dopant concentrations (Y) of 15 and 18 atom%, near the solubility limit of Ti(4+) in the fluorite structure, have been introduced to achieve a high electronic conductivity at low oxygen partial pressure. The yttrium content x has been varied between 15 and 25 atom% to find the fluorite composition with the highest ionic conductivity for each titanium level. In the pO(2)-range from 0.21 to 10(-13) atm the conductivity is predominantly ionic and constant over that range. The maximum ionic conductivity is 0.01 Scm(-1) for the compositions, which contain 15 atom% yttrium. Substantial electronic conductivity is introduced into the system at low oxygen pressures below 10(-13) atm via reduction of Ti(4+) ions to Ti(3+) The maximum electronic conductivity of 0.2 Scm(-1) at 930 degrees C has been measured for a sample with 18 atom% titanium. The slope of all log(sigma) vs. log(pO(2)) plots follows a pO(2-)(1/4)-dependence.