DC Sputtering of yttria-stabilised zirconia films for solid oxide fuel cell applications

Yttria-stabilised zirconia (YSZ) thin films were dc-sputtered and investigated with respect to surface morphology, microstructure and film-substrate interface interaction. The films were deposited under argon/oxygen atmospheres on NiO/YSZ substrates heated to between 500 and 700°C. Dense and crack-free coatings were obtained in the thickness range of 1 to 10 μm. The film morphology varied from columnar to crystalline structure depending on the oxygen pressure and the substrate temperature. Whereas the coated films consisted of YSZ with cubic and tetragonal crystal structure under low oxygen atmospheres, the same deposition experiments on Al2O3 substrates revealed highly disordered layers of cubic YSZ. The formation of oxide layers on the NiO/YSZ substrates is due to a film-substrate redox interaction. The NiO grains close to the coating interface are partially reduced and serve as an oxygen source for the oxidation of the film. An exponential decay of the gas leakage vs. coating thickness was found.