A promising approach used to fabricate YBa2Cu3O7-delta (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 degrees 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 degrees C step at 3 degrees 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 (p) for the normal state (100 K) shows an increasing sequence of rho (3 degrees C h(-1)) < p (10 degrees C h(-1)) < rho(1.5 degrees C h(-1)). In this experiment set-up, the highest J(c) value of 1.3 x 10(6) A cm(-2) (77 K, self-field) was achieved with a 3 degrees C h(-1) heating rate, which can be correlated with texture and microstructural observations.
Available at: http://works.bepress.com/sharmila_mukhopadhyay/61/