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 concentra tions was measured at 1200 degrees-1600 degrees C. In the oxide system s, the cubic phase was identified using X-ray diffractometry. All dopa nt oxides formed wide cubic solid-solution regions with HfO2. In the H fO2-Y2O3 system, the 15 mol% Y2O3 composition featured the lowest para meter p(e') and, thus, represented the optimum composition for a solid electrolyte. For the investigated RE(2)O(3)-doped HfO2 solid solution s, the parameter p(e') decreased as the dopant radius decreased. The l owest parameter p(e') values among the RE(2)O(3)-doped systems were ob tained for HfO2-Dy2O3 or HfO2-Yb2O3 at 1600 degrees C. Furthermore, pa rameter p(e') values were determined for the fluorite- and pyrochlore- type structures in the HfO2-Gd2O3 system and ternary oxide solutions b ased on HfO2. Additional investigations confirmed the good reproducibi lity of the parameter p(e') values using two different measuring metho ds and different sintering conditions for the HfO2-30 mol% Y2O3 compos ition. A comparison between the parameter p(e') values of doped HfO2 a nd ZrO2 systems revealed that the parameter p(e') values of HfO2 syste ms were one to three orders of magnitude lower than those of ZrO2 syst ems in the 1200 degrees-1600 degrees C temperature range.