The development of Y Ba₂Cu₃O_<i>x</i> thin films using a fluorine-free sol–gel approach for coated conductors

Abstract

Despite great success in the TFA methods of depositing Y Ba2Cu3Ox (YBCO) thin films for coated conductors, critical issues involved in removing BaCO3 have not entirely been settled. There could be other possible ways of dealing with carbon that remains in the film. We have recently developed a fluorine-free sol–gel synthesis with several important advantages including precursor solution stability, improved film density, and elimination of HF during processing. With this approach, high-quality YBCO films have been developed on single crystal substrates with the transport Jc s up to 106 A cm−2. In this study, the precursor solution stoichiometry was altered and its effects on superconducting properties were studied. The fluorine-free sol–gel-derived films on the LaAlO3 (LAO) substrate exhibited epitaxial growth with excellent in- and out-of-plane texture. Experimental details are reported on the sol–gel synthesis chemistry and XRD and TEM characterization of the YBCO thin films. Also discussed is the underlying formation mechanism of the YBCO phase during the synthesis.