Preparation and characterization of epitaxial La0.5Sr0.5CoO3 films and of an all a-axis oriented YBa2Cu3O7-y/La0.5Sr0.5CoO3/YBa2Cu3O7-y heterostructure on (001) LaAlO3 by pulsed laser deposition

Thin films of La0.5BSr0.5CoO3 (LSCO) with very smooth surfaces were prepared in situ by pulsed laser deposition on (100) LaA1O(3) substrates. X-ray diffraction in Bragg-Brentano and four-circle geometry confirmed that full epitaxial LSCO films can be grown for a much wider deposition temperature range, 500-730 degrees C, than that reported previously. Resistivity versus temperature measurements revealed that the LSCO films grown at temperatures lower than 650 degrees C were metallic. However, those fabricated at higher deposition temperatures showed a semiconducting transport behaviour, similar to that of oxygen-deficient LSCO films grown at the lower temperatures. X-ray photoelectron spectra of the Sr 3d core level suggested that this change in transport behaviour may be caused by cation disorder as well as oxygen deficiency involved in the high-temperature deposition. An all a-axis oriented YBa2Cu3O7-y/La0.5Sr0.5CoO3/YBa2CU3O7-y (YBCO/LSCO/YBCO) heterostructure was fabricated successfully for the first time, which further confirms that the conductive LSCO film is promising for fabrication of high-T-c superconductor-normal metal-superconductor junctions.