HIGH CRYSTALLINE QUALITY CEO2 BUFFER LAYERS EPITAXIED ON (1(1)UNDER-BAR-02) SAPPHIRE FOR YBA2CU3O7 THIN-FILMS

(0 0 1)CeO2 thin films and bilayer (0 0 1)YBa2Cu3O7/(0 0 1)CeO2 films grown in situ by pulsed laser deposition (PLD) on single crystal(1 (1) under bar 0 2) sapphire have been investigated. CeO2 buffer layers ex hibit single crystal-like quality as proven by the full-width at half- maximum (FWHM) of the 0 0 2 rocking curve (Delta theta similar to 0.03 degrees) and the channeling minimum yield measured by baskscattering spectrometry (RBS) (chi(min)similar to 3%). Therefore, the YBa2Cu3O7/C eO2/Al2O3 heterostructures present sharp interfaces as shown by the ob servation of Laue oscillations on both CeO2 and YBa2Cu3O7 XRD patterns . In agreement with this crystalline perfection, YBa2Cu3O7 thin films present excellent and reproducible superconducting properties: T-c (R = 0) > 88.5 K, transition width similar to 0.5 K and microwave surface resistance R-s 0.5-2 m Omega at 10 GHz and 77 K. (C) 1998 Elsevier Sc ience B.V. All rights reserved.