Mixed (oxygen ion and n-type) conductivity and structural characterization of titania-doped stabilized tetragonal zirconia
- CSIC, Madrid (Spain)
- CSIC-Univ. de Sevilla, Madrid (Spain)
By using X-ray diffraction lattice parameter measurements and Raman spectroscopy studies, both the solid solubility limit of titania in yttria tetragonal zirconia polycrystalline solid solutions (Y-TZP, 3 mol % Y{sub 2}O{sub 3}) and the TiO{sub 2}-YTZP tetragonal solid solution field in the ZrO{sub 2}-Y{sub 2}O{sub 3}-TiO{sub 2} system have been established. Valence state, site symmetry, and changes in local structures of Ti ions in Y-TZP with 5 and 10 mol % TiO{sub 2} are studied for the first time using EXAFS (extended X-ray absorption fine structure), XANES (X-ray absorption near edge structure), and X-ray photoelectron spectroscopy. The total electrical conductivity in air of the TiO{sub 2}-Y-TZP tetragonal solid solution decreases with increasing titania content. XANES results show that as the TiO{sub 2} dissolves into the tetragonal zirconia Y-TZP matrix, a displacement of Ti{sup 4+} ions from the center of symmetry seem to take place which leads to a non-random substitution of Ti{sup 4+} ions on Zr{sup 4+} lattice sites. Ti-O bond distances derived from EXAFS results indicate that Ti{sup 4+} ion can be in a square-pyramidal arrangement, i.e., fivefold oxygen-coordinated. As a consequence, two kinds of cation-oxygen vacancy associations with different diffusion dynamics are created. The results in a decrease of the global concentration of moving oxygen vacancies and therefore, a decrease of ionic conductivity. Electronic conductivity, n-type, only appeared at oxygen partial pressure lower than 10{sup {minus}15} atm and above 800 C in Y-TZP containing 10 mol % titania. Such an n-type electronic conduction was attributed to a hopping of electrons between Ti{sup 4+} and Ti{sup 3+} cations by a small polaron hopping mechanism.
- OSTI ID:
- 680040
- Journal Information:
- Journal of the Electrochemical Society, Vol. 146, Issue 7; Other Information: PBD: Jul 1999
- Country of Publication:
- United States
- Language:
- English
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