Review of a chemical approach to YBa2Cu3O7 x-coated superconductors—metalorganic deposition using trifluoroacetates

Large-area, uniform, high critical current density ( J c ) YBa 2 Cu 3 O 7− x (YBCO) superconductor films are now routinely obtained by metalorganic deposition using trifluoroacetates (TFA-MOD). This method does not require any expensive vacuum apparatus at any time during the whole process. Thus, TFA-MOD is regarded as one of the most suitable candidates for fabricating a YBCO tape for many high-power applications. This method originated from an electron beam process using BaF 2 developed by Mankiewich et al . Afterwards, Gupta et al reported using TFA-MOD to prepare a similar precursor film. These two ex situ processes used fluorides instead of BaCO 3 to avoid the fatal deterioration in J c , which is caused in the resulting films through metal carboxylic groups. Fluorides not only avoid such deterioration but also lead to perfectly c -axis-oriented epitaxial crystal growth. In conventional metalorganic deposition, nucleation in the precursor film causes random orientation in the resulting film. However, in TFA-MOD, nanocrystallites in the precursor film never cause such disorder. Furthermore, during the firing process of TFA-MOD, water and HF gas diffuse quickly between the film surface and growth front of the YBCO layer. This diffusion never limits the growth rate of YBCO. What distinguishes TFA-MOD from conventional metalorganic deposition? What happens during heat treatment? In this paper, we discuss all the TFA-MOD processes and the peculiar growth scheme of the YBCO layer in TFA-MOD using the model of a quasi-liquid network. In addition, we review the history of TFA-MOD and recent results and discuss the prospects of future applications.