Structural and electrical characterization of titania-doped YSZ

Solid solutions and composites based on YSZ yttria-stabilized zirconia) with titania additions up to 20 mol% were prepared by solid state reaction. Structural characterization included XRD and Raman spectroscopy. Electroded samples were also studied by impedance spectroscopy in air between 573 and 1273 K. The ionic conductivity of these solid solutions decreases with increasing titania content. A sharp drop in conductivity is observed for specimens with compositions near to the usually assumed solubility limit of titania in the fluorite phase (about 10 mol%). This decrease is of almost one order of magnitude with respect to undoped or lightly doped samples. A smaller composition dependence is observed for higher titania additions (10-20 mol% TiO2). Raman results show that tetragonal short range order is found in the cubic fluoritic phase well below the 10 mol% TiO2 addition. This short range order is expained by the ability of Ti to achieve a sixfold oxygen coordination. As a consequence, a decrease in the concentration of mobile oxygen vacancies is expected, which is the reason for the electrical conductivity decrease. (C) 1997 Elsevier Science Limited.