Growth distinctions of GdBa Cu O films on 1012/sapphire

The growth of epitaxial superconducting GdBa2Cu3O7yd films on 1012.sapphire without buffer layer.has been investigated. The films have been grown in situ by pulsed laser deposition. The critical current density of 100-nm-thick films was above 106Arcm2 77 K.and the surface resistance was 40 mV 77 K.at the frequency 75.2 GHz. The 300-nm-thick films detached from the substrate have been investigated by high resolution electron microscopy. It has been shown that the film consists of c-oriented single crystal grains about 0.5 mm in size. In the a,b plane each grain is oriented in one of the two directions on the substrate surface along thew2021xorw0221xsapphire axes.. The differently oriented grains are connected via small angle boundaries of 3–48. Such a film structure is caused by the lattice mismatch between GdBa2Cu3O7yd and 1012.sapphire. With increasing film thickness above 120 nm, the development of cracks along the small angle boundaries and degradation of superconducting properties takes place. q1998 Elsevier Science B.V.