Author: Patricia Álvarez

X. Obradors, T. Puig, A. Pomar, F. Sandiumenge, N. Mestres, M. Coll, A. Cavallaro, N. Roma, J. Gazquez, J. C. Gonzalez, O. Castano, J. Gutierrez, A. Palau, K. Zalamova, S. Morlens, A. Hassini, M. Gibert, S. Ricart, J. M. Moreto, S. Pinol, D. Isfort and J. Bock Supercond. Sci. Technol. 19, S13-S26 (2006) DOI:10.1088/0953-2048/19/3/003 Chemical solution deposition (CSD) has recently emerged as a very competitive technique for obtaining epitaxial films of high quality with controlled nanostructure. In particular, the all-CSD approach is considered to be one of the most promising approaches for cost-effective production of second-generation superconducting wires. The trifluoroacetate (TFA) route is a very versatile route for achieving epitaxial YBa₂Cu₃O₇ (YBCO) layers with high critical currents. In this work, recent advances towards improvement of the performance of several conductor architectures based on the YBCO TFA process will be presented. We show that new improved anhydrous TFA precursors allow a significant shortening of the pyrolysis time (~1.5 h), and we have increased the total film thickness in a single deposition using polymeric additives. On the other hand, further understanding of the YBCO nucleation and growth process has allowed us to obtain a controlled microstructure and high critical currents (J_c≈4–5 MA cm⁻² and I_c≈300 A cm⁻¹ width at 77 K). The growth conditions (CSD) and post-processing conditions (sputtering and CSD) for the underlying oxide cap and buffer layers (CeO₂, BaZrO₃, SrTiO₃, La₂Zr₂O₇, (La,Sr)MnO₃) and of self-organized nanostructures (CeO₂, BaZrO₃) deposited by CSD have been investigated to obtain high-quality interfaces in multilayered systems. Different single-crystal or metallic substrates (YSZ-IBAD (yttrium stabilized zirconia-ion beam assisted deposition) and Ni-RABiT (rolling assisted biaxial texturing)) have been investigated and long (≈10 m) CSD biaxially textured buffers (CeO₂, La₂Zr₂O₇) have been grown on Ni-RABiT substrates using a reel-to-reel system. High-performance TFA-YBCO-coated conductors have been obtained on vacuum-based buffer layers (I_c≈140 A cm⁻¹ width) and on CSD buffer layers grown on IBAD YSZ-SS (stainless steel) substrates. Finally, we report on recent analysis of the magnetic granularity and vortex pinning properties of TFA-YBCO conductors.

T. Puig, J. C. Gonzalez, A. Pomar, N. Mestres, O. Castano, M. Coll, J. Gazquez, F. Sandiumenge, S. Pinol and X. Obradors Supercond. Sci. Technol. 18, 1141-1150 (2005) DOI: 10.1088/0953-2048/18/8/020 The influence of three processing parameters, temperature, gas flow rate and water pressure, on the YBa₂Cu₃O₇ film growth on LaAlO₃ single-crystal substrates from trifluoroacetate precursors has been investigated and the optimal film processing conditions to achieve high critical currents have been determined. We have found that the growth conditions maximizing the critical current density are those where the nucleation of a-axis oriented grains is minimized, as determined by μ-Raman spectroscopy. Under these conditions the normal state resistivity is very near to that of single crystals because a vanishingly small film porosity is achieved. Transmission electron microscopy analysis of films quenched from the growth temperature gives some hints for understanding the mechanism linking the film porosity with the concentration of a-axis grains. A cross-linked influence of different processing parameters, such as temperature and water pressure, or water pressure and gas flow, has been demonstrated. The optimal growth temperatures are 790–830 °C, but at these growth temperatures, the critical current density is still dependent on the gas flow rate and water pressure. The optimal processing ranges are a compromise between two different competing phenomena influencing the quality of the films: inhomogeneous film formation due to HF gas stagnancy at small nominal growth rates (low gas flow rate or water pressure) and perturbed crystallinity at high gas flow rates or water pressures.