Elucidation of the decomposition reactions of low-fluorine YBa2Cu3O7-x precursors during film pyrolysis

Chemical solution deposition methods such as low-fluorine metal organic decomposition, are nowadays widely employed in the production of YBa2Cu3O7-x superconducting films. The investigation of the chemical reactions that convert the organic precursors into the pyrolysis product is essential for the optimization of the pyrolysis step, and, ultimately, for the comprehension of the growth process. In this work, a detailed analysis of the single-salt precursors, of the ternary precursor solution and its thermal decomposition was carried out through infrared spectroscopy (FITR), thermogravimetric analysis (TGA), evolved gas analysis (EGA), X-Ray diffraction (XRD), coupled with quench experiments, and X-Ray photoelectron spectroscopy (XPS). The combination of these techniques led to the identification of the precursors and the proposal of a reaction path for pyrolysis. More in detail, a copper/ammonia coordination compound was identified and it is the first to decompose at low temperatures via a mixed path of hydrolysis and oxidation to produce copper oxide. The decomposition of the other two precursors is superimposed at higher temperatures and it yields a mixture of BaF2, YF3 and Ba1-xYxF2+x.