Importance of the pyrolysis for microstructure and superconducting properties of CSD-grown GdBa$_{2}$Cu$_{3}$O$_{7-x}$-HfO$_{2}$ nanocomposite films by the ex-situ approach

For the first time, GdBa$_{2}$Cu$_{3}$O$_{7-x}$ nanocomposites were prepared by chemical solution deposition following the ex-situ approach. In particular, ~ 220 nm GdBa$_{2}$Cu$_{3}$O$_{7-x}$-HfO$_{2}$ (GdBCO-HfO$_{2}$) nanocomposite films were fabricated starting from a colloidal solution of 5 mol% HfO2 nanoparticles. Hereby, one of the main challenges is to avoid the accumulation of the nanoparticles at the substrate interface during the pyrolysis, which would later prevent the epitaxial nucleation of the GdBCO grains. Therefore, the effect of pyrolysis processing parameters such as heating ramp and temperature on the homogeneity of the nanoparticle distribution has been investigated. By increasing the heating ramp to 300 °C/h and decreasing the final temperature to 300 °C, a more homogenous nanoparticle distribution was achieved. This translates into improved superconducting properties of the grown films reaching critical temperatures (T$_{c}$) of 94.5 K and self-field critical current densities (𝐽$_{c}$$^{sf}$) at 77 K of 2.1 MA/cm$^{2}$ with respect to films pyrolyzed at higher temperatures or lower heating ramps.