Atmospheric plasma-spraying (APS) is an attractive process for the production of solid oxide fuel cell layers. However, especially the manufacture of gas-tight electrolyte layers is a major challenge as typical APS ceramic coatings contain microcracks and pores which allow an easy penetration of gases. To overcome this problem a detailed understanding of the formation of microcracks and pores in the coating was developed. These ideas and the conclusions made will be described in detail. Major influencing factors were identified to be substrate temperature, particles temperature and velocity, particle size, and the way the plasma gun is moved. According to the outcome of these considerations spraying experiments have been performed with different yttria stabilized zirconia (YSZ) powders including spray dried and fused and crushed types. Porous, tape-casted metallic plates were used as substrates. Employed measures for the coating optimization lead to a significant reduction of both length and opening of the microcracks. These results were in accordance with the outcome of leakage tests. It was possible to improve the leakage rates by several orders of magnitude and to achieve sufficiently low values for an application as solid oxide fuel cell electrolyte without any subsequent thermal treatment.