Trajectory-property relationships in MOD-derived YBCO films

A study of the physical and chemical changes during processing in MOD-derived YBCO films was performed. Fully processed films were 70-85% of theoretical density. The sintering rate increased substantially in the compositional range F/Ba = 1.8-1.5. The activation energy for sintering decreased above a P(H2O) dependent threshold temperature. XRD indicated this temperature/composition threshold also corresponded to YBCO nucleation, suggesting ex situ YBCO forms in contact with a melt. The ramp rate and P(H2O) were used to control F/Ba trajectories, which were correlated to performance. The nucleation of YBCO was strongly dependent on processing conditions. Nucleation temperature was varied by at least 60 °C in the study. The optimal YBCO nucleation temperature in the 300-800 nm films was around 725 °C. a-axis grains dominated the microstructures of films where YBCO nucleated at <700 °C. Large second phases, but no a-axis grains, were found when the nucleation temperature was >750 °C.