Thermal Stability and Phase Transformation in Fully Indium Oxide (ino1.5) Stabilized Zirconia

Indium oxide (InO1.5) stabilized zirconia (InSZ) is an attractive material as electrolyte, or electrode, in solid oxide fuel cells (SOFCs), and as corrosion resistant top coat in thermal barrier coatings. However, little is known about the phase stability of cubic InSZ at temperatures that simulate the conditions in an operating SOFC or turbine. This article provides an investigation of the phase stability and phase transformations in cubic InSZ after heat treatments at 800, 1000, and 1200°C for periods up to 2000h. The results revealed that cubic InSZ is not stable during annealing at 1000 and 1200°C, owing to a fast destabilization of the initial cubic phase to tetragonal, and eventually to monoclinic (c→t→m). The c→t→m transition in InSZ is intimately associated with the indium volatilization. On the other hand, cubic InSZ remained stable for 2000h at 800°C, although the partial formation of the tetragonal phase was observed along with a 0.25% contraction in the unit cell volume of the cubic phase, caused by short-range ordering. These results demonstrate that technological applications of cubic InSZ are restricted to temperatures at which the volatilization of the InO1.5 stabilizer does not occur.