Plasma sprayed oxygen transport membrane coatings

Oxygen and hydrogen transport membranes fabricated by plasma spray deposition of a micro-crack-free coating on a substrate. Also disclosed is a multi-layer composite comprising a dense or porous substrate coated with a coating provided by supersonic plasma spray deposition. Also disclosed is subsonic plasma spray deposition of single phase or dual phase nanocrystalline particles to form a crack-free oxygen transport membrane on a substrate.