Institut de Ciencia de Materials de Barcelona, Spain1
Tel Aviv University, Israel2
Growth of epitaxial REBa2Cu3O7 (REBCO) films on buffered sapphire substrates has awaken the interest of different research group for some time. Sapphire is an attractive substrate for device applications, like Superconducting Fault Current Limiters (SCFCL), due to its properties: high thermal conductivity, stability at high temperatures, good mechanical strength.
However, YBCO films cannot be grown directly on sapphire substrates due to the chemical reactivity of YBCO with Al2O3. For that reasons appropriate buffer layers are required, such as CeO2 or YSZ. An additional issue is the formation of microcracks in YBCO films. Several attempts to overcome this problem have been reported using physical deposition methods and different strategies for strain - relieving.
Chemical Solution Deposition is a low cost and robust methodology to scale up YBCO films which can be used to growth coated conductors and thick films[1]. To develop SFCL applications long length sapphire substrates are required and so CSD growth is very appealing Long length sapphire substrates, however, are barely polished and so it is required to optimize the CSD YBCO growth on intermediate quality polished substrates.
Here we report a study of CSD YBCO film growth on CeO2/YSZ/sapphire substrates and we analyze the role of the surface roughness on the epitaxial quality of YBCO films. Also the issue of the microcracks generation is further investigated in relationship to the film thickness, the growth process and the oxygenation annealing step. We demonstrate that microcracks formation is not related to differential thermal expansion effects and that it can be controlled through an adapted oxygenation step.
We conclude that CSD growth of YBCO films with attractive superconducting properties (Jc ~1.9 MA/cm2 at 77 K) can be prepared on long length barely polished sapphire substrates .
[1] Pop C, Villarejo B, Pino F, Mundet B, Ricart S, De Palau M, Puig T and Obradors X 2019 Growth of all-chemical high critical current YBa 2 Cu 3 O 7-δ thick films and coated conductors Supercond. Sci. Technol. 32
[2] A. Saraf, B.Almog, M.Azoulay, and G. Deutscher, “Sapphire-basedSFCL conductors,” in Superconducting Fault Current Limiter. Singapore: World Scientific Publishing, 2018, pp. 357–372.Scientific Publishing, 2018, pp. 357–372.
Keywords: critical currents, YBCO/sapphire, CSD growth, thick films