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

Abstract

Listen

Translate article

A promising approach used to fabricateYBa2Cu3O7−δ (YBCO) thin films is the metal–organic deposition (MOD) method usingtrifluoroacetate (TFA) solution. In this method, the heating rate is known to be acrucial parameter and an important variable for optimization. However, theredoes not seem to be an in-depth understanding of the materials issues associatedwith different heating rates. Some aspects of this correlation have been addressedin this paper, where the influence of the heating rate during calcination in the200–250 °C temperature range on the surface chemistry, morphology, and electrical properties has beenstudied. X-ray photoelectron spectroscopy reveals similar chemical compositions and almostcomplete decomposition of metal trifluoroacetates at all heating rates. However, the heatingrate is seen to have a significant influence on the morphology of the calcined film, andleads to great changes in the final film. When a TFA film is heated through the200–250 °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 tothe final reacted films having very different microstructures. A uniform,c-axis oriented microstructure is observed in the3 °C h−1 heated films. A slower heating rate results in a large density ofa-axis oriented grains and a faster heating rate causes higher pore density together with a biggeraverage pore size. Although all films exhibit high phase purity YBCO with noticeablec-axis orientation, theelectrical resistivity (ρ) for the normal state (100 K) shows an increasing sequence ofρ(3 °C h−1)<ρ(10 °C h−1)<ρ(1.5 °C h−1). In this experimentset-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.