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

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-doped YTZP ([%mol]3 Y₂O₃) compositions sintered in the temperature range of 1300 to 1450 °C, the tetragonal zirconia solid solutions field for the ZrO₂-Y₂O₃-TiO₂ system was established. The solubility of TiO₂ in YTZP was found to be about 12–[%mol]14 at 1450 °C. Structural characterization of the Ti-YTZP tetragonal zirconia solid solutions was carried out using X-ray absorption spectroscopy (EXAFS and XANES) to provide information on the environment of Ti atoms. The electrical behavior in air of the TiO₂-doped tetragonal zirconia solid solutions was studied by impedance spectroscopy in the temperature range of 300 to 800 °C, and it was found that the ionic conductivity 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 distances derived from EXAFS indicate that the Ti ion can be in a square-pyramidal 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 oxygen-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.