Precursor Evolution and Nucleation Mechanism of YBa₂Cu₃O_x Films by TFA Metal−Organic Decomposition

Abstract

We describe the conversion of yttrium, barium, and copper trifluoracetate-derived solid precursors to epitaxial YBa 2 Cu 3 O x superconducting ceramics on (001)-oriented LaAlO 3 substrates. Transmission electron microscopy, electron energy loss spectroscopy, energy-dispersive X-ray analysis, and X-ray diffraction are used to characterize the reaction path and nucleation mechanism yielding high critical current YBa 2 -Cu 3 O 7 . Our results show that the pyrolysis of the trifluoracetate solutions yields a nanostructured, partially amorphous Ba 1-x Y x F 2+x matrix having a Ba/Y ratio close to 2, with homogeneously dispersed CuO nanoparticles. Upon heating, the chemical trajectory of the fluoride matrix and the overall microstructural evolution of the ceramic precursor prior to YBa 2 Cu 3 O 7 nucleation is driven by the decomposition and oxidation of this solid solution. The Y solid solubility decreases with temperature yielding Y 2 O 3 which reacts with the CuO particles forming Y 2 Cu 2 O 5 at about 700°C. In addition, electron energy loss spectroscopy reveals a high oxygen concentration and almost no Y in the matrix quenched from 795°C, at a stage where the YBa 2 Cu 3

A Modular Ex Situ Conversion Process for Thick MOD-Fluoride RBCO Precursors

“…In the proposed fluoride decomposition reaction, this phase is assumed to be the primary source of ions. Like other reaction equations proposed in the literature [1]- [4], this equation highlights the roles of gaseous reactants and and product HF, which provide the connection to controllable process parameters.…”

Thickness control of solution deposited YBCO superconducting films by use of organic polymeric additives

“…This result allows us to conclude that the PEG additives do not modify the porosity of the films after pyrolysis. 19,32 Thus, with 30% PEG in the solution and coating at 6000 rpm, the pyrolyzed films are ∼1200 nm thick and the growth process transforms them in YBCO films of ∼620 nm thickness. From Fig.…”

Nucleation and growth rate influence on microstructure and critical currents of TFA-YBa2Cu3O7 under low-pressure conditions

“…During the later step, the exact reaction mechanism of YBCO conversion is complex. It depends on the intermediate phase evolution 8,9 and, to a certain degree, on the pyrolysis conditions 10,11 and actually it is still not fully revealed. Based on our previous studies [6][7][8]12 and those of others, [13][14][15][16] Eq.…”