Influence of Substrate-Film Reactions on YBCO Grown by Fluorine-Free MOD Route

Recently, fluorine-free metal organic deposition routes (FF-MOD) for growth of YBCO superconducting films have attracted increased attentions. In this paper, a comparison study was performed on the YBCO-Ag superconducting thin films deposited on two types substrates, LaAlO₃ and CSD-Ce_0.9La_0.1O_2-y (CLO)/YSZ, respectively. Although conventional TFA-MOD derived YBCO films exhibit high performance on both substrates, the results vary when using the FF-MOD precursor. SEM and XRD results reveal that c-axis and a/b-axis orientations coexist in the YBCO-Ag films grown on the CSD-CLO/YSZ substrate deposited by the FF-MOD route, while the BaCeO₃ by-product is a dominating phase in the fully reacted film. Based on the structural analysis of the partially converted films, we found that interfacial reactions between the film and the CLO cap layer play an essential role on the epitaxial growth of YBCO-Ag films from the FF-MOD solution. Because of the different chemical reaction path compared to conventional TFA-MOD routes, it seems that the polycrystalline BaCeO₃ formation takes place prior to the YBCO-Ag epitaxial growth associated with the melting process, which results in structural deterioration at high growth temperatures and, therefore, no superconductivity. This study indicates the necessity of further reducing the nucleation temperature of YBCO films processed by FF-MOD routes.