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 exhibit 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/CeO2/Al2O3 heterostructures present sharp interfaces as shown by the observation 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 Science B.V. All rights reserved.