Structural properties of plasma-sprayed zirconia-based electrolytes

Zirconia-based electrolytes, stabilized either with yttrium oxide or calcium oxide, were prepared in 100 to 200 µm thick layers by plasma spraying and densified by high-temperature vacuum sintering. The structure and the microstructure were investigated by optical microscopy, scanning electron microscopy, X-ray diffraction and Raman spectroscopy. The results are compared with the data we obtained on the powders used for plasma spraying and on single crystals. In the zirconia-yttria system, dense and fully stabilized zirconia films with structural properties similar to the corresponding single crystals were obtained. On the other hand, cracks and deformations were observed on calcia-stabilized films. This phenomenon is explained by the dramatic increase of monoclinic phase content due to the preferential evaporation of calcium oxide which occurs during high-temperature vacuum sintering.