Film thickness dependence of microstructure and superconductive property of PLD prepared YBCO layers
Highlights
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Highly c-axis oriented YBCO layers were obtained on RABiTS substrates by PLD.
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NiO and BaCeO3 will be formed during the YBCO growth.
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Increasing film thickness will degrade the alignment of YBCO and CeO2.
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Increasing film thickness will decline the surface quality and Jc.
Introduction
YBCO coated conductor is expected to satisfy the requirements of numerous electric applications at liquid nitrogen temperature [1], [2]. To achieve the necessary bi-axial alignment, YBCO coated conductors are primarily made using the ion beam assisted deposition (IBAD) [3], rolling assisted bi-axially textured substrate (RABiTS) [4], or in-clined substrate deposition (ISD) processes [5]. The RABiTS consists of layers of metal oxide buffers epitaxially deposited with either a cube-on-cube or rotated cube-on-cube orientation to the {1 0 0} 〈1 0 0〉 textured Ni or Ni-alloy substrates [6], [7], [8]. These ceramic buffer layers act as a barrier against Ni diffusion from the base metal substrate into the YBCO layer while providing a template of reduced lattice mismatch between YBCO and Ni for epitaxial growth.
The Pulse Laser Deposition (PLD) method has been widely used as a convenient and efficient process for producing high quality YBCO films on various substrates due to high deposition rate and film stoichiometry close to the target [9], [10]. However, growth of thicker YBCO films that maintain adequate critical current density (Jc) is difficult. The mechanisms that lead to degradation in the films can stem from the development of a-axis grains or porosity, formation of nonsuperconducting phases, oxygen deficiencies, and changes in stoichiometry [11]. In this investigation, YBCO layers of varying thicknesses were deposited on RABiTS having a CeO2/YSZ/Y2O3/NiW architecture by PLD. Deposition conditions, crystal alignment, microstructure, and superconducting property were studied.
Section snippets
Experimental
Y2O3 (120 nm), YSZ (200 nm), CeO2 (40 nm) were subsequently deposited on NiW (5%) substrates using DC reactive magnetron sputtering in a reel-to-reel system. The full width at half maximum (FWHM) values of φ-scan (△φ) and ω-scan (△ω) of the buffer layers were about 6–7° and 3–4°, respectively, and the detailed information was described in previous work [12].
YBCO films were deposited on CeO2/YSZ/Y2O3/NiW substrates by PLD using KrF (=248 nm) excimer laser. Stoichiometric YBCO target with 50 mm
Results and discussion
The YBCO films were deposited on CeO2/YSZ/Y2O3 buffered NiW substrates by PLD, and the buffer layers only have single-phased (l 0 0) orientation, indicating excellent c-axis texture described in a previous report [12]. A set of YBCO films deposited at the same condition with a thickness range of 0.4–2.33 μm was studied. Typical XRD θ–2θ scans of YBCO are shown in Fig. 1. The major peaks in the pattern correspond to the (0 0 l) diffractions of YBCO phase, indicating that all YBCO films are highly c
Conclusions
YBCO films with various thicknesses have been deposited on CeO2/YSZ/Y2O3/NiW substrates by PLD. The results of XRD θ–2θ scan revealed that YBCO films were highly c-axis oriented, though there were small NiO (1 1 1) peaks in all samples. Furthermore, Y2O3 and YSZ layers remained excellent bi-axial texture, while the alignment of CeO2 got worse after YBCO deposition. As the thickness of YBCO increased, the amount of a-axis grains and BaCeO3 increased, and the in-plane orientation and surface
Acknowledgement
We would like to thank Kai Shi of Tsinghua University for his help in the SEM observation.
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