Preparation and conductivity of ternary scandia-stabilised zirconia

Cubic scandia-stabilised zirconia (ScSZ) has a very high oxygen ion conductivity, significantly higher than the more common yttria-stabilised zirconia (YSZ). However, its practical use is hindered by an ordered rhomboedric phase being present at low temperature which is unique for zirconias. The occurrence of this phase can be suppressed by co-doping scandia-stabilised with ternary metal oxides. It is the aim of this study to investigate the influence of co-doping with various cations on the ionic conductivity, and on the phase transition towards lower temperatures. To do that, we prepared scandia-stabilised zirconia containing 10 mol%Sc2O3 and up to 1.0 mol% Gd2O3, CaO, or CeO2, respectively, using a sol-gel method starting with nitrates of the metals. Powders were sintered at 1500 degrees C to obtain dense material with grain sizes in the range of 0.5 to 1.0 mu m. An addition of more than 0.5 mol% Gd2O3 significantly decreased the transition temperature of the phase transition between cubic and rhombohedral. The low temperature AC conductivity, measured in the range of 400 to 950 degrees C, was highest for ScSZ containing 1 mol% CeO2. The Arrhenius plot was strongly curved, indicating association or ordering of oxygen vacancies, which were explained with literature models. (C) 2010 Elsevier B.V. All rights reserved.