EPITAXIAL CEO2 BUFFER LAYERS FOR YBA2CU3O7-DELTA FILMS ON SAPPHIRE

Epitaxial CeO2 buffer layers and YBa2Cu3O7-delta thin films have been grown in situ on (1102BAR) sapphire by electron beam evaporation. Buff er layers of only 20 nm thickness inhibit interdiffusion between YBa2C u3O7-delta and Al2O3 as determined by depth profiling using x-ray phot oelectron spectroscopy. The layers show smooth surfaces and narrow int erfaces. High lattice perfection of the CeO2 layer has been shown by x -ray diffraction. Laue oscillations up to ninth order have been observ ed in thin CeO2 buffer layers on sapphire. We found only one epitaxial orientation with YBa2Cu3O7-delta (001) \\ CeO2 (001) \\ Al2O3 (1102BA R) and YBa2Cu3O7-delta [110] \\ CeO2 [100] \\ Al2O3 [1120BAR]. YBa2Cu3 O7-delta films grown on these buffer layers reveal T(c) = 88+/-0.5 K, rho(300 K) = 380 muOMEGA cm, and j(c)(77 K, 0 T) = 1.3 X 10(6) A/cm2.