CeO2 compatibility with YBa2Cu3O72d in superconducting-film multilayers

High-quality superconducting ~Tc'90 K, j c.10 6 A/cm at 77 K! epitaxial ~001! YBa2Cu3O72d films were grown by laser ablation on ~001! CeO2 /(11I02) Al2O3. An interaction between YBa2Cu3O72d and CeO2 would influence the structure and the superconducting parameters. A marked degradation of the superconducting transition temperature (Tc574 K) was observed when twenty 2-nm-thick CeO2 layers were inserted equidistantly into a ~001! YBa2Cu3O72d film ~200 nm!. BaCeO3 crystalline inclusions were detected by x-ray diffraction. X-ray-absorption fine-structure investigations at the Cu-K edge indicate that Ce substitutes for Y in YBa2Cu3O72d. Near-edge x-ray-absorption studies indicate that the valence of Ce incorporated into the YBa2Cu3O72d regions of the multilayer structure is also 14. @S0163-1829~97!04541-4#