Effect of titania doping and sintering temperature on titanium local environment and electrical conductivity of YSZ

Abstract The effect that the titania doping and the sintering temperature has on the relationship between the titanium local environment and the electrical properties of YSZ has been studied. To this end, materials obtained for different titania additions ranging from 5 to 30 mol%, and sintered at different temperatures, have been studied. The combined results obtained by XRD, FT-Raman, and FE-SEM-EDX clearly indicate that titania causes the formation of both a titania-doped YSZ solid solution and a titania-doped YTZP solid solution. When the concentration of TiO 2 reaches 20 mol% zirconium titanate, that admits Y 2 O 3 in solid solution, crystallizes. In addition to these three main phases, Y 2 (Ti 1-y Zr y ) 2 O 7 pyrochlore is also detected as minor phase for titania contents from 10 to 20 mol%. In the case of composites obtained for a fixed 10 mol% titania content varying the sintering temperatures leads only to a variation of the relative amount of the two main titania-doped YSZ and titania-doped YTZP phases. The total ionic conductivity of the composites, measured by impedance spectroscopy, decreases as the titania content increases, showing a sharp drop for doping concentrations above 15 mol%. In agreement with these results the Ti K-edge X-ray absorption spectroscopy (XAS) study shows that this behavior has been related not only to the sequential crystallization of the different phases but also to the ability of Ti to trap oxygen vacancies due to its occurrence in a disordered sixfold Ti O arrangement. In contrast, the variation of the sintering temperature has little influence on both the ionic conductivity and the composite structure.