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 pr epared in situ by pulsed laser deposition on (100) LaA1O(3) substrates . X-ray diffraction in Bragg-Brentano and four-circle geometry confirm ed that full epitaxial LSCO films can be grown for a much wider deposi tion temperature range, 500-730 degrees C, than that reported previous ly. Resistivity versus temperature measurements revealed that the LSCO films grown at temperatures lower than 650 degrees C were metallic. H owever, those fabricated at higher deposition temperatures showed a se miconducting transport behaviour, similar to that of oxygen-deficient LSCO films grown at the lower temperatures. X-ray photoelectron spectr a of the Sr 3d core level suggested that this change in transport beha viour may be caused by cation disorder as well as oxygen deficiency in volved in the high-temperature deposition. An all a-axis oriented YBa2 Cu3O7-y/La0.5Sr0.5CoO3/YBa2CU3O7-y (YBCO/LSCO/YBCO) heterostructure wa s fabricated successfully for the first time, which further confirms t hat the conductive LSCO film is promising for fabrication of high-T-c superconductor-normal metal-superconductor junctions.