Structural characterization and mixed conductivity of TiO2-doped ceria stabilized tetragonal zirconia

By using X-ray diffraction lattice parameter measurements and Raman spectroscopy studies. the solid solubility limits of titania in ceria tetragonal zirconia solid Solutions (12 mol% CeO2) have been established. Electrical properties of the mixed conductor TiO2-Ce-TZP containing 5 and 10 mol% TiO2 were measured at the 300degreesC-900degreesC temperature range. The total electrical conductivity in air of the TiO2-Ce-TZP ceramics decreases with titania content due to Ti-Vo associations. which depresses the mobility of the oxygen vacancies during the conduction process. The electrical behaviour of undoped-Ce-TZP solid solutions as a function of the pO(2) and temperature showed that in oxidising conditions and up to an oxygen partial pressure of 10(-9) Pa the materials were nearly pO(2) independent, Under lower oxygen partial pressure the total electrical conductivity increases according to pO(2)(-1.6) indicating that the n-type conduction in Ce-TZP is due to the electron hopping between Ce4+ and Ce3+ cations. In Ce-TZP containing 5 and 10 mol% titania the electrical behaviour,vas very different mainly under the most reducing conditions. Above 800 degreesC and with decreasing oxygen partial pressure below 10(-9) Pa, the theoretical correlation for electronic conduction was near to n proportional to pO(2)(-1.4), which indicates that the conduction process is controlled by the Ce-Zr' and Ti-Zr' defect concentrations. by hopping of the electrons between Ce4+ and Ce3- and Ti4+ and Ti3+ via a small polaron hopping mechanism. (C) 2002 Published by Elsevier Science Ltd and Techna S.r.l.