Effects of heat treatment and film thickness on microstructure and critical properties of YBCO film processed by TFA-MOD

We fabricated YBCO film on an LAO substrate using the TFA-MOD method and evaluated the effects of the heat treatment temperature and film thickness on the microstructure, degree of texture, and critical properties. The calcining and firing processes were performed in the temperature ranges of 370-460 °C and 750-800 °C, respectively. We found that the phase purity, grain size and orientation, and degree of texture varied with the calcining and firing temperatures. The films fired at 775 °C after calcining at 400-430 °C showed the highest critical temperature (T_C-onset) of 89.5 K and critical current (I_C) of 40 A/cm-width, which corresponds to a critical current density (J_C) of 1.8 MA/cm². According to the XRD, pole-figure, SEM images, and Raman analysis, these highest critical properties are probably due to the formation of a purer YBCO phase and stronger biaxial texture. In the multi-coated films, the I_C value increased from 39 to 169 A/cm-width as the number of coatings increased from one to four, while the corresponding J_C was measured to be in the range of 0.8-1.2 MA/cm². Both the I_C and J_C decreased when a further coating was applied due to the degradation of the microstructure.