Smooth stress relief of trifluoroacetate metal-organic solutions for YBa2Cu3O7 film growth

摘要

The mechanisms controlling stress relief during the drying and pyrolysis processes of trifluoroacetate metal-organic precursors have been elucidated in view of high rate fabrication of epitaxial superconducting YBa2Cu3O7 thin films. Combining FTIR, TGA, and film thickness evolution measurements, we conclude that gel drying and sintering occurs below T similar to 250 degrees C while film densification, due to metal-organic pyrolysis, occurs in the range 250-310 degrees C. Stress relief is the driving force leading to smooth or structurally inhomogeneous films, displaying buckling or macrocracks, depending on the rate of film transformation. High heating rates can be used during the gel drying and sintering process preserving the film homogeneity because the developed stress is below that required to generate buckling, as demonstrated by nanoindentation experiments. Within the temperature window where the metal-organic decomposition process occurs, the gas flow and the temperature ramp can be tuned to achieve fast pyrolysis preserving the film homogeneity. Optical microscopy, TEM, SEM, AFM, nanoindentation, mu-Raman spectroscopy, electrical resistivity, and critical current measurements of the films have been combined to stress the relevance of preserving the homogeneity of the films from the nanometric to the macroscopic length scales, to achieve high critical current YBa2Cu3O7 thin films, i.e., J(c) approximate to 3-4 MA/cm(2) at 77 K.