Phase Transition During Heat Treatment of Precursor Before YBaCuO Nucleation in TFA-MOD Method.

This work presents a study of the evolution of the phases in the intermediate heat treatment process (IHP) which was after the pyrolysis process and before the crystallization of YBCO superconducting thin films. It was shown that the evolution of the solid solution could always take place whether with or without water vapor and oxygen. When water vapor is present in the atmosphere, the evolution temperature of the intermediate phase was lower than the one without vapor. The intermediate phase of YCuO with the vapor was observed at 680 °C. By calculating the changes of Gibbs free energy of reactions possibly involved in the IHP, the priority reaction with water vapor was CuF>YF>BaF when CuF, YF, and BaF coexisted while CuF and YF prefer to react with BaO to form BaF while they coexisted. The appearance of intermediate phase features could be illustrated through the calculation. [ABSTRACT FROM AUTHOR]