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Silvia Rasi1 Julia Jareño2 Laia Soler2 Juri Banchewski2 Roger Guzman2 Susagna Ricart2 Jordi Farjas1 Pere Roura1 Cristian Mocuta3 Xavier Obradors2 Teresa Puig2

1, University of Girona, Girona, Catalonia, Spain
2, ICMAB, Institut de Ciencia de Materials de Barcelona (CSIC), Cerdanyola del Valles, Catalonia, Spain
3, Synchrotron SOLEIL, Gif-sur-Yvette Cedex, Île-de-France, France

Nowadays, the application of high temperature superconducting tapes for energy transport and electrical power devices is limited by its production cost. Therefore, it is of the utmost importance to develop a cost-effective synthetic route of high-throughput YBa2Cu3O7 (YBCO) film growth. Chemical solution deposition of metal organic precursors (CSD-MOD) is known to be a good candidate to fulfil this challenge. YBCO growth rates for the traditional route based on fluorinated precursors are limited by the very low HF out-diffusion during BaF2 decomposition.
On the other hand, Y2O3 diffusion through BaO-CuO melts is known to be very high, thus enabling high growth rates. We propose a CSD route using fluorine free (FF) precursors that, upon proper decomposition of BaCO3, follows the formation of a transient liquid that results from the eutectic reaction between BaO and CuO. The YBCO layers obtained from this Transient Liquid Assisted Growth (TLAG) method achieve epitaxial films with superconducting transition temperatures of 90 K and critical current densities at 77 K of 3 MA/cm2.
In this communication, we present two different methods to grow YBCO with the desired c-axis orientation: the temperature-step route and the PO2-step route. In the first case, very high heating rates (20-60 °C/s) at a constant pressure force the system to reach the correct region of the phase diagram for the epitaxial growth, and where the precursors (BaCO3) are fully decomposed. By contrast, in the second route, precursor decomposition and YBCO growth are decoupled, by decomposing BaCO3 at low PO2 (~10-6/10-7 bar) where YBCO growth is prevented. Afterwards, an increase of O2 partial pressure results in YBCO epitaxial growth. To understand the growth process and reaction paths, advanced high-resolution Scanning Transmission Electron Microscopy (STEM), In-situ x-ray diffraction, and synchrotron radiation have been employed. Growth rates between 25 and 50 nm/s have been achieved.
Finally, we will also show the compatibility of the TLAG process with the growth of nanocomposites using preformed nanoparticles of BaZrO3.

Acknowledgements

This work was partially funded by MINECO (project MAT2014-51778-C2); Generalitat de Catalunya (contract 2014SGR-00948); Universitat de Girona (contract MPCUdG2016/059); Center of Excellence award Severo Ochoa (SEV-2015-0496) and ERC-2014-ADG-669504-ULTRASUPERTAPE

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