Properties of epitaxial YBa2Cu3O7 thin films on Al2O3 {1̄012}

Epitaxial YBa2Cu3O7 films were grown on Al2O3 {1̄012} by a laser ablation technique. X-ray diffraction shows that films are epitaxial with the c axis perpendicular to the substrate surface and ‘‘123’’ [110] aligned with sapphire [101̄1], although the full width at half maximum of the rocking curve is larger than those of epitaxial films on SrTiO3. Typical Tc’s are between 85 and 88 K with transition widths between 0.5 and 3 K. The normal-state resistivity is 270 μΩ cm at 300 K and extrapolates to zero at zero temperature while the magnetization Jc is as high as 5×106 A/cm2 at 4.2 K. High-frequency loss measurements show that 2000-Å-thick epitaxial films on Al2O3 {1̄012} have a surface impedance about 1 mΩ at 13 GHz at 4.2 K.