THE TRANSMISSION ELECTRON-MICROSCOPY INVESTIGATION AND ELECTRICAL-PROPERTIES OF EPITAXIAL TL-1223 AND BISUBSTITUTED T1-1223 THIN-FILMS GROWN BY IN-SITU LASER-ABLATION

Tl1Ba2Ca2Cu3Ox thin films, with and without Bi-substitution, have been fabricated by in-situ laser ablation on (001) SrTiO3 and (001) LaAlO3 substrates. Using transmission electron microscopy and allied techniq ues, the films have been characterised in cross-section. In the case o f films grown without Bi-substitution, heavily defected microstructure s with a-axis oriented grains and stacking-type planar defects resulti ng in discontinuous a-b planes have been observed. Films fabricated wi th Bi-substitution have highly defected microstructures within about 1 50 nm of the substrate, with considerably less faulting further from t he substrate where the bulk of the superconducting currents flow and t he microwave properties are primarily determined. Bi-substituted films have been fabricated with critical current density values up to 8 x 1 0(5) A cm(-2) (77 K) and surface resistances values as low as 56 m Ohm (77 K, 87 GHz), which is equivalent to 0.74 m Ohm at 10 GHz, assuming a frequency-squared relationship. (C) 1998 Elsevier Science B.V. All rights reserved.