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A promising approach used to fabricate YBa2Cu3O7−δ (YBCO) thin films is the metal–organic deposition (MOD) method using trifluoroacetate (TFA) solution. In this method, the heating rate is known to be a crucial parameter and an important variable for optimization. However, there does not seem to be an in-depth understanding of the materials issues associated with different heating rates. Some aspects of this correlation have been addressed in this paper, where the influence of the heating rate during calcination in the 200–250 °C temperature range on the surface chemistry, morphology, and electrical properties has been studied. X-ray photoelectron spectroscopy reveals similar chemical compositions and almost complete decomposition of metal trifluoroacetates at all heating rates. However, the heating rate is seen to have a significant influence on the morphology of the calcined film, and leads to great changes in the final film. When a TFA film is heated through the 200–250 °C step at 3 °C h−1, it has a smooth and uniform surface. On the other hand, a slower heating rate (1.5 °C h−1) results in phase separation during calcination, and a faster heating rate (10 °C h−1) leads to a rough film decorated with micron-scale pores. This leads to the final reacted films having very different microstructures. A uniform, c-axis oriented microstructure is observed in the 3 °C h−1 heated films. A slower heating rate results in a large density of a-axis oriented grains and a faster heating rate causes higher pore density together with a bigger average pore size. Although all films exhibit high phase purity YBCO with noticeable c-axis orientation, the electrical resistivity (ρ) for the normal state (100 K) shows an increasing sequence of ρ(3 °C h−1)< ρ(10 °C h−1) <ρ(1.5 °C h−1). In this experiment set-up, the highest Jc value of 1.3 × 106 A cm−2 (77 K, self-field) was achieved with a 3 °C h−1 heating rate, which can be correlated with texture and microstructural observations.

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A new route, starting from nanoparticles of mixed ions, has been used to synthesize high-quality thin films of a complex perovskite (YBa2Cu3O7−δ, YBCO). Currently, the most promising approach for making YBCO films uses metal trifluoroacetates. In comparison, the present method using a colloidal dispersion of nanoparticles is seen to produce crystalline, well textured films at much faster heating rates and having much lower porosity. Whereas there is scope for further optimization, this effort has rapidly yielded superconducting films with transition temperature of 89.5 K and self-field critical current density up to 2.4 MA cm−2 at 77 K.

Detailed investigation of superconducting films of YBa 2 Cu 3 O 7-d (YBCO) prepared from solution-based precursors have been performed. Two precursors have been compared in this study: the presently used trifluoroacetate (TFA) solution and a recently developed colloidal suspension containing nanoparticles of mixed oxide. Detailed analyses of the evolution of microstructure and chemistry of the films have been performed, and process parameters have been correlated with final superconducting properties. Both films need two heating steps: a low temperature calcination and a higher temperature crystallization step. For TFA films, it was seen that the heating rate during calcination needs to be carefully optimized and is expected to be slow. For the alternate process using a nanoparticle precursor, a significantly faster calcination rate is possible. In the TFA process, the Ba ion remains as fluoride and the Y remains as oxyfluoride after calcination. This implies that, during the final crystallization stage to form YBCO, fluorine-containing gases will evolve, resulting in residual porosity. On the other hand, the film from the nanoparticle process is almost fully oxidized after calcination. Therefore, no gases evolve at the final firing (crystallization) stage, and the film has much lower porosity. The superconducting properties of both types of films are adequate, but the nanoparticle films appear to have persistently higher J c values. Moreover, they show improved flux pinning in higher magnetic fields, probably due to nanoscale precipitates of a Cu-rich phase. In addition, the nanocolloid films seem to show additionally enhanced flux pinning when doped with minute amounts of second phase precipitates. It therefore appears that, whereas the TFA process is already quite successful, the newly developed nanoparticle process has significant scope for additional improvement. It can be scaled-up with ease, and can be easily adapted to incorporate nanoscale flux pinning defects for in-field performance.