4.5　mol%　yttria-stabilized　zirconia　(YSZ)　coating　was　deposited　by　atmospheric　plasma　spraying　(APS)　as　an　electrolyte　for　solid　oxide　fuel　cells　(SOFCs)　applications.　The　post　treatment　was　employed　using　zirconium　and　yttrium.　nitrate　solution　infiltration　to　densify　the　coating　microstructure　for　improvement　of　gas　permeability.　The　deposition　of　YSZ　through　nitrate　in　voids　of　the　coating　was　examined.　Microstructure　of　the　as-sprayed　and　densified　coatings　was　characterized　by　scanning　electron　microscopy　(SEM)　and　transmission　electron　microscopy　(TEM).　The　effect　of　infiltrating　treatment　on　coating　microstructure　and　electrical　conductivity　was　examined.　The　electrical　conductivity　of　APS-sprayed　YSZ　coating　at　the　direction　perpendicular　to　coating　surface　was　much　lower　than　that　of　bulk　materials.　Post-densification　treatment　improved　the　electrical　conductivity　of　YSZ　coating　by　about　25%　compared　with　as-sprayed　coating.　It　was　found　that　the　deposition　of　YSZ　resulting　from　decomposition　of　nitrate　in　the　lamellar　interface　gaps　was　different　from　that　in　vertical　cracks　in　lamella　owing　to　the　orthogonal　feature　of　those　two　types　of　gaps.　The　nanopores　were　formed　in　the　deposited　YSZ　in　nonbonded　interface　gaps　while　large　pores　were　residued　in　vertical　cracks　in　splats.　The　microstructural　examination　suggests　that　nanopores　in　the　deposited　YSZ　in　nonbonded　interfaces　in　the　coating　were　isolated　from　each　other,　which　led　to　the　significant　reduction　of　gas　permeability　after　densification.　Moreover,　the　nanocontacts　between　lamellae　resulted　in　high　contact　resistance　and　limit　improvement　of　electrical　conductivity　of　the　coating　after　densification.　(c)　2006　Elsevier　B.V.　All　rights　reserved.