Effect of the tantalum oxide addition in the phase composition and electrical conductivity in the zirconium-10% mol Scandia

Abstract

Scandia-stabilized zirconia (ScSZ) based compositions are alternative electrolyte systems to the conventional yttria stabilized zirconia (YSZ) for solid oxide fuel cells (SOFCs) operating at intermediate temperatures (500-700 °C). ScSZ exhibits higher ionic conductivity (~10 mS.cm-1) than YSZ and has a high ionic transference number (~1.0) under reducing conditions. However, the cubicrhombohedral phase transition at ~600ºC causes a considerable decrease in ionic conductivity, hindering its use in technological applications. The introduction of a second additive promotes the stabilization of the cubic phase at room temperature and suppresses the deleterious phase transition. In this work the effect of the addition of small amounts (up to 0.50 mol%) of tantalum oxide in the phase composition and in the electrical conductivity of the zirconia-10% mol scandia is investigated. Double doping samples were prepared by the conventional mixing method followed by solid state reaction. The compacts obtained by uniaxial pressing were sintered in air at 1500ºC for 5 h. Samples containing at least 0.40 mol% of additive showed stabilization of the cubic phase at room temperature. The impedance spectroscopy results showed an increase in grain conductivity for compositions containing at least 0.35 mol% tantalum oxide. These results show that it is possible to use tantalum oxide in small amounts to suppress the cubic-rhombohedral phase transition, and to increase the zirconia-scandia electrical conductivity at low temperatures.