Smooth Stress Relief of Trifluoroacetate Metal-Organic Solutions for YBa 2 Cu 3 O 7 Film Growth Katerina Zalamova,* Neus Roma `, Alberto Pomar, Stephanie Morlens, Teresa Puig, Jaume Ga ´zquez, Anna E. Carrillo, Felip Sandiumenge, Susana Ricart, Narcı ´s Mestres, and Xavier Obradors Institut de Cie ` ncia de Materials de Barcelona, CSIC, Campus de la UAB, 08193 Bellaterra, Catalonia, Spain ReceiVed July 6, 2006 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 YBa 2 Cu 3 O 7 thin films. Combining FTIR, TGA, and film thickness evolution measurements, we conclude that gel drying and sintering occurs below T ∼ 250 °C while film densification, due to metal-organic pyrolysis, occurs in the range 250-310 °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, μ-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 YBa 2 Cu 3 O 7 thin films, i.e., J c ≈ 3-4 MA/cm 2 at 77 K. I. Introduction Chemical solution deposition (CSD) is a cost-effective technique with a high potential for preparation of functional large area and long length films. 1 Many oxides with electronic, electrical, ferroelectric, dielectric, magnetic, or superconducting functionalities have been prepared by CSD having either a polycrystalline or an epitaxial structure. 2-7 High-temperature superconducting coated conductors are one example where preparation of high-quality epitaxial thin films with long lengths is required and, therefore, CSD is a promising alternative to the conventional physical deposition techniques. 8-13 One of the challenges of the solution-based deposition processes, however, is to avoid the formation of microstructural inhomogeneities, which could influence their functionality, during any of the steps converting the deposited chemical solution into the crystalline film. 14-16 This process consists of one or two steps, depending on the compliance of the films during the densification, pyrolysis, and crystal- lization processes. In a single-step process the removal of the organic constituents and the oxide crystallization occur simultaneously while in the two-step process they are separately accomplished. Several characterizations of the metal-organic precursor chemistry (reactivity and decompo- sition temperature) and the complex rearrangement leading to amorphous or nanocrystalline phases resulting from the pyrolysis will determine the choice of a given process. Some ferroelectric oxides, for instance, can be prepared through a one-step rapid thermal annealing process (>100 °C/s) without formation of cracks or blisters. 2 Trifluoroacetate (TFA) metal-organic decomposition (MOD) has been largely in- vestigated as a chemical solution route leading to high-quality YBa 2 Cu 3 O 7 (YBCO) superconducting films with high critical * To whom correspondence should be addressed. E-mail: kzalamova@ icmab.es. 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Technol. 2000, 19, 205. 5897 Chem. Mater. 2006, 18, 5897-5906 10.1021/cm061556+ CCC: $33.50 © 2006 American Chemical Society Published on Web 11/09/2006