High-temperature ionic conduction in multicomponent solid oxide solutions based on HfO2

The parameter p(e') of HfO2-CaO, HfO2-Y2O3, and HfO2-RE(2)O(3) (where RE is a rare-earth element) solid solutions with high dopant concentrations was measured at 1200 degrees-1600 degrees C. In the oxide systems, the cubic phase was identified using X-ray diffractometry. All dopant oxides formed wide cubic solid-solution regions with HfO2. In the HfO2-Y2O3 system, the 15 mol% Y2O3 composition featured the lowest parameter p(e') and, thus, represented the optimum composition for a solid electrolyte. For the investigated RE(2)O(3)-doped HfO2 solid solutions, the parameter p(e') decreased as the dopant radius decreased. The lowest parameter p(e') values among the RE(2)O(3)-doped systems were obtained for HfO2-Dy2O3 or HfO2-Yb2O3 at 1600 degrees C. Furthermore, parameter p(e') values were determined for the fluorite- and pyrochlore-type structures in the HfO2-Gd2O3 system and ternary oxide solutions based on HfO2. Additional investigations confirmed the good reproducibility of the parameter p(e') values using two different measuring methods and different sintering conditions for the HfO2-30 mol% Y2O3 composition. A comparison between the parameter p(e') values of doped HfO2 and ZrO2 systems revealed that the parameter p(e') values of HfO2 systems were one to three orders of magnitude lower than those of ZrO2 systems in the 1200 degrees-1600 degrees C temperature range.