Photoelectron spectroscopic investigation of transformation of trifluoroacetate precursors into superconducting YBa_2Cu_3O_(7-δ) films

摘要

X-ray photoelectron spectroscopy (XPS) has been used to investigate the evolution of surface chemistry of YBa_2Cu_3O_(7-δ) (Y123) films prepared by the metalorganic deposition (MOD) process using trifluoroacetate (TFA) precursors. Detailed XPS core-level spectra obtained from the samples quenched from various points during the calcining and firing stages have been reported for the first time and are used to identify surface species. The XPS data show evidence of formation of intermediate phases such as Y-O-F, BaF_2, and CuO during the calcining process, which are the decomposition products of yttrium, barium, and copper trifluoroacetates, respectively. The TFA precursors are completely decomposed at the end of calcination. The change of binding energies for Y 3d_(5/2), Ba 3d_(5/2), and O 1s during the firing process indicates that Y123 starts to form at 800℃ after 0.5 h firing. Based on the experimental results, an alternative mechanism of the chemical evolution from precursor to final film in the TFA-MOD process is proposed.