Substrate effects on the properties of Y-Ba-Cu-O superconducting films prepared by laser deposition

Superconducting thin films of Y1Ba2Cu3Ox with superconducting transition temperature (Tc) near 90 K have been prepared by a laser deposition technique. We show that films prepared on sapphire, lithium niobate, and strontium titanate under identical processing conditions exhibit different electrical characteristics. The film surfaces, interfaces, and crystallinity have been studied by a number of analytical techniques. We conclude that the substrate influences the film properties primarily in three ways: the thermal expansion mismatch introduces cracks in the film, the interface reaction changes the film composition, and the substrate lattice influences the crystallographic orientation of the film.