Improvements in the microstructure of YBa2Cu3O7-δ films on sapphire with self-assembled CeO2 buffer layers

Abstract YBa 2 Cu 3 O 7− δ (YBCO) films were grown by pulsed laser deposition on CeO 2 -buffered Al 2 O 3 (1  1  0 2) substrates. Prior to the superconducting film deposition, a high-temperature O 2 annealing was performed, which induces a surface reconstruction in CeO 2 film. The microstructure of YBCO films on sapphire with both as-grown and annealed CeO 2 buffer layers was investigated by transmission electron microscopy. For the YBCO on the as-grown CeO 2 buffer layer, many surface outgrowths were found, originating from interfacial reactions of YBCO with the CeO 2 film and the Al 2 O 3 substrate. For the YBCO film on the annealed CeO 2 buffer layer, however, the interfacial reactions as well as the surface outgrowths were drastically inhibited. Instead, there are a high density of nanometer-sized precipitates, which are egg-shaped and elongated along c -axis of YBCO. The precipitates are identified as Y 2 Cu 2 O 5 .