The influence of the heating rate on YBCO films prepared by the trifluoroacetate metal–organic deposition process

Abstract

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.

Fabrication of thin films of multi-cation oxides (YBa2Cu3O7−δ) starting from nanoparticles of mixed ions

“…In the TFA-MOD process, the calcination takes over 20 h [8], whereas here it takes about 6 h. This is followed by a high-temperature annealing in humid argon/oxygen gas mixture at 800 • C for 1 h in a low oxygen partial pressure (P (O2) = 200 ppm). This 5 h step is similar to that used by the TFA-MOD process, which has been described in detail elsewhere [9].…”

Solution-Based Approaches to Fabrication of YBa2Cu3O7−δ (YBCO): Precursors of Tri-Fluoroacetate (TFA) and Nanoparticle Colloids

“…Detailed analyses at every step of the heating process are explained in earlier publications. 10,11 The comparison of the calcined films (which clearly differentiates the intermediate phases for the two precursors) is shown here. Figure 5 shows the comparative XPS spectra of Y 3d, Ba 3d, and Cu 2p obtained from the samples after calcination using the nanoparticle and the conventional TFA-MOD processes.…”

The fabrication of YBa2Cu3O7−xfilm by metal–organic deposition using terpineol-modified trifluoroacetates

“…However, during the pyrolysis process, the thermal decomposition of TFA precursor films results in a drastic reduction in film thickness and is accompanied by an increase of internal stress in the films. Therefore, the gel films prepared by the standard TFA-based precursor are very susceptible to cracking at decomposition temperatures, especially at temperatures from 200 to 250 • C. In order to avoid cracking in the film, the original temperature-time profile developed for the calcination required nearly 10-20 h [2][3][4][5]. However, this long process time is not compatible with a low-cost manufacturing process.…”