Structure-electrical properties relationships in TiO2-doped stabilized tetragonal zirconia ceramics

The tetragonal zirconia solid solution field in the ternary system ZrO2-Y2O 3-TiO2 has been established, and the influence of TiO2 addition on the elec trical properties of the formed ternary Ti-YTZP solid solutions has also be en studied. The unit cell parameters determined from the X-ray diffraction patterns of the sintered samples, and the data obtained from X-ray absorpti on (XANES and EXAFS) were used to provide information on the environment of Ti atoms. The electrical conductivity of the Ti-YTZP tetragonal solid solu tions decreases with increasing titania concentration. EXAFS and XANES resu lts show that as the TiO2 dissolves into the tetragonal zirconia YTZP matri x, a displacement of Ti4+ ions from the center of symmetry seems to take pl ace which leads to a state of non-random substitution of Ti4+ ions on Zr4lattice sites. Ti-O bond distances derived from EXAFS indicate that Ti ions can be in a square-pyramidal arrangement, i.e. five-fold oxygen coordinate d. As consequence, two kinds of cation-oxygen vacancy associations with dif ferent diffusion dynamics are created. This results in a decrease in the gl obal concentration of moving oxygen vacancies and, therefore, in a decreasi ng of the ionic conductivity. (C) 1999 Elsevier Science Ltd and Techna S.r. l. All rights reserved.