Structure and electrical behavior in air of TiO2-doped stabilized tetragonal zirconia ceramics

From the lattice parameters determined by XRD on TiO2-doped YTZP (3 mol % Y 2O3) compositions sintered in the temperature range of 1300 to 1450 degrees C, the tetragonal zirconia solid solutions field for the ZrO2-Y2O3-TiO2 sy stem was established. The solubility of TiO2 in YTZP was found to be about 12-14 mol % at 1450 degrees C. Structural characterization of the Ti-YTZP t etragonal zirconia solid solutions was carried out using X-ray absorption s pectroscopy (EXAFS and XANES) to provide information on the environment of Ti stems. The electrical behavior in air of the TiO2-doped tetragonal zirco nia solid solutions was studied by impedance spectroscopy in the temperatur e range of 300 to 800 degrees C, and it was found that the ionic conductivi ty decreases with increasing titania content. EXAFS and XANES results show that as the Ti4+ ions dissolve into the tetragonal zirconia YTZP matrix, a displacement of Ti ions from the center of symmetry takes place, leading to a non-random substitution of Ti4+ ions on Zr4+ lattice sites. Ti-O bond di stances derived from EXAFS indicate that the Ti ion can be in a square-pyra midal arrangement, i.e., fivefold oxygen coordinated. As a consequence two kinds of cation-oxygen vacancy associations are created; the high-mobility oxygen-vacancy-eightfold-coordinated cation (Zr4+) and the low-mobility oxy gen-vacancy-fivefold-coordinated cation (Ti4+). This results in a decrease in the global concentration of moving oxygen vacancies and, therefore, in a decrease of the electrical conductivity.