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Fabrication and characterization of La2Zr2O7 films on different buffer architectures for YBa2Cu3O7-δ coated conductors by RF magnetron sputtering.

Xu D, Liu L, Xiao G, Li Y - Nanoscale Res Lett (2013)

Bottom Line: The in-plane texture of LZO film on CeO2 single-buffer architecture was ∆ φ = 5.5° and the out-of-plane texture was ∆ ω = 3.4°.All the LZO films had very smooth surfaces, but LZO films grown on YSZ/CeO2 and CeO2/YSZ/CeO2 buffer architectures had cracks.The highly textured LZO film grown on CeO2-seed buffered NiW tape was suitable for the epitaxial growth of YBCO film with high currents.

View Article: PubMed Central - HTML - PubMed

Affiliation: Research Center of Applied Superconductivity and Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, People's Republic of China. yjli@sjtu.edu.cn.

ABSTRACT
La2Zr2O7 (LZO) films were grown on different buffer architectures by radio frequency magnetron sputtering for the large-scale application of YBa2Cu3O7-x (YBCO)-coated conductors. The three different buffer architectures were cerium oxide (CeO2), yttria-stabilized zirconia (YSZ)/CeO2, and CeO2/YSZ/CeO2. The microstructure and surface morphology of the LZO film were studied by X-ray diffraction, optical microscopy, field emission scanning electron microscopy, and atomic force microscopy. The LZO films prepared on the CeO2, YSZ/CeO2, and CeO2/YSZ/CeO2 buffer architectures were preferentially c-axis-oriented and highly textured. The in-plane texture of LZO film on CeO2 single-buffer architecture was ∆ φ = 5.5° and the out-of-plane texture was ∆ ω = 3.4°. All the LZO films had very smooth surfaces, but LZO films grown on YSZ/CeO2 and CeO2/YSZ/CeO2 buffer architectures had cracks. The highly textured LZO film grown on CeO2-seed buffered NiW tape was suitable for the epitaxial growth of YBCO film with high currents.

No MeSH data available.


AFM photographs of LZO films. Grown on the (a) CeO2, (b) YSZ/CeO2, and (c) CeO2/YSZ/CeO2 buffer architectures.
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Figure 5: AFM photographs of LZO films. Grown on the (a) CeO2, (b) YSZ/CeO2, and (c) CeO2/YSZ/CeO2 buffer architectures.

Mentions: xTo investigate the films deeply and broadly, the surface morphologies of LZO films fabricated on CeO2, CeO2/YSZ, and CeO2/YSZ/CeO2 buffered NiW tapes are observed by OM, SEM, and AFM. From optical photographs shown in Figure 3, it is demonstrated that the surface of all LZO films on CeO2, CeO2/YSZ, and CeO2/YSZ/CeO2 buffered NiW tapes are all flat without any island or particle in the area of 1 mm × 1 mm. Only a few grain boundaries are observed in the surfaces of LZO films. The surfaces of LZO films are flat enough in a large area with only shallow grain boundaries. This indicates that LZO buffer layers are suitable for the sequential epitaxial growth of YBCO films. In Figure 4, SEM images also indicate that all the LZO films deposited on three different buffer architectures have excellent smooth surface. Figure 4a shows that the LZO film grown on CeO2 seed layer has no microcrack and is flat without any island in the area of 3 μm × 4 μm. However, in Figure 4b,c, microcracks are observed in LZO films grown on YSZ/CeO2 and CeO2/YSZ/CeO2 buffered NiW tapes, which resulted from the film structural stress when the thickness of the entire buffer layer exceeds the critical value. The thicknesses of CeO2 seed layer, YSZ buffer layer, and CeO2 cap layer are 50, 100, and 200 nm, respectively. The thickness of the LZO buffer layer grown on single CeO2, YSZ/CeO2, and CeO2/YSZ/CeO2 buffered NiW substrates are the same which is 100 nm. When the thicknesses of all buffer layers exceed the critical value of 200 nm, cracks appear in LZO films grown on the YSZ/CeO2 and CeO2/YSZ/CeO2 buffer architectures. LZO films grown on YSZ/CeO2 and CeO2/YSZ/CeO2 buffer architectures with the thickness of the buffer layer less than the critical value are shown in Figure 4d,e, respectively. From the pictures of Figure 4d,e, it is clear that LZO films have no microcracks, but small particles on the surfaces have the number density of 30/μm2. Tapping mode AFM images in Figure 5 illustrated that the root mean square (RMS) surface roughness of LZO films grown on CeO2-seed, YSZ/CeO2, and CeO2/YSZ/CeO2 buffer architectures were 1.2, 1.9, and 2.5 nm in the scanning area of 5 μm × 5 μm. The surface of the LZO film becomes much rougher when the thickness of the entire buffer layer is increased. The grain size of particles on the surface of the LZO film is about 0.2 μm in diameter. The grain-boundary depths of LZO films prepared on CeO2-seed, YSZ/CeO2, and CeO2/YSZ/CeO2 buffer architectures are about 10 nm, and the grain-boundary widths are approximately 1 μm. These results indicate that LZO films grown on the CeO2-seed, YSZ/CeO2, and CeO2/YSZ/CeO2 buffer architectures are indeed high quality. Figure 5a shows the LZO film grown on CeO2 seed layer is flat and dense with no cracks. In Figure 5b,c, LZO films grown on the YSZ/CeO2 and CeO2/YSZ/CeO2 buffer architectures are also flat and dense but are cracked. These results are corresponding with the results of SEM observations. The cracks in LZO film will give rise to decrease in Jc of upper YBCO superconducting layer.


Fabrication and characterization of La2Zr2O7 films on different buffer architectures for YBa2Cu3O7-δ coated conductors by RF magnetron sputtering.

Xu D, Liu L, Xiao G, Li Y - Nanoscale Res Lett (2013)

AFM photographs of LZO films. Grown on the (a) CeO2, (b) YSZ/CeO2, and (c) CeO2/YSZ/CeO2 buffer architectures.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3750552&req=5

Figure 5: AFM photographs of LZO films. Grown on the (a) CeO2, (b) YSZ/CeO2, and (c) CeO2/YSZ/CeO2 buffer architectures.
Mentions: xTo investigate the films deeply and broadly, the surface morphologies of LZO films fabricated on CeO2, CeO2/YSZ, and CeO2/YSZ/CeO2 buffered NiW tapes are observed by OM, SEM, and AFM. From optical photographs shown in Figure 3, it is demonstrated that the surface of all LZO films on CeO2, CeO2/YSZ, and CeO2/YSZ/CeO2 buffered NiW tapes are all flat without any island or particle in the area of 1 mm × 1 mm. Only a few grain boundaries are observed in the surfaces of LZO films. The surfaces of LZO films are flat enough in a large area with only shallow grain boundaries. This indicates that LZO buffer layers are suitable for the sequential epitaxial growth of YBCO films. In Figure 4, SEM images also indicate that all the LZO films deposited on three different buffer architectures have excellent smooth surface. Figure 4a shows that the LZO film grown on CeO2 seed layer has no microcrack and is flat without any island in the area of 3 μm × 4 μm. However, in Figure 4b,c, microcracks are observed in LZO films grown on YSZ/CeO2 and CeO2/YSZ/CeO2 buffered NiW tapes, which resulted from the film structural stress when the thickness of the entire buffer layer exceeds the critical value. The thicknesses of CeO2 seed layer, YSZ buffer layer, and CeO2 cap layer are 50, 100, and 200 nm, respectively. The thickness of the LZO buffer layer grown on single CeO2, YSZ/CeO2, and CeO2/YSZ/CeO2 buffered NiW substrates are the same which is 100 nm. When the thicknesses of all buffer layers exceed the critical value of 200 nm, cracks appear in LZO films grown on the YSZ/CeO2 and CeO2/YSZ/CeO2 buffer architectures. LZO films grown on YSZ/CeO2 and CeO2/YSZ/CeO2 buffer architectures with the thickness of the buffer layer less than the critical value are shown in Figure 4d,e, respectively. From the pictures of Figure 4d,e, it is clear that LZO films have no microcracks, but small particles on the surfaces have the number density of 30/μm2. Tapping mode AFM images in Figure 5 illustrated that the root mean square (RMS) surface roughness of LZO films grown on CeO2-seed, YSZ/CeO2, and CeO2/YSZ/CeO2 buffer architectures were 1.2, 1.9, and 2.5 nm in the scanning area of 5 μm × 5 μm. The surface of the LZO film becomes much rougher when the thickness of the entire buffer layer is increased. The grain size of particles on the surface of the LZO film is about 0.2 μm in diameter. The grain-boundary depths of LZO films prepared on CeO2-seed, YSZ/CeO2, and CeO2/YSZ/CeO2 buffer architectures are about 10 nm, and the grain-boundary widths are approximately 1 μm. These results indicate that LZO films grown on the CeO2-seed, YSZ/CeO2, and CeO2/YSZ/CeO2 buffer architectures are indeed high quality. Figure 5a shows the LZO film grown on CeO2 seed layer is flat and dense with no cracks. In Figure 5b,c, LZO films grown on the YSZ/CeO2 and CeO2/YSZ/CeO2 buffer architectures are also flat and dense but are cracked. These results are corresponding with the results of SEM observations. The cracks in LZO film will give rise to decrease in Jc of upper YBCO superconducting layer.

Bottom Line: The in-plane texture of LZO film on CeO2 single-buffer architecture was ∆ φ = 5.5° and the out-of-plane texture was ∆ ω = 3.4°.All the LZO films had very smooth surfaces, but LZO films grown on YSZ/CeO2 and CeO2/YSZ/CeO2 buffer architectures had cracks.The highly textured LZO film grown on CeO2-seed buffered NiW tape was suitable for the epitaxial growth of YBCO film with high currents.

View Article: PubMed Central - HTML - PubMed

Affiliation: Research Center of Applied Superconductivity and Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, People's Republic of China. yjli@sjtu.edu.cn.

ABSTRACT
La2Zr2O7 (LZO) films were grown on different buffer architectures by radio frequency magnetron sputtering for the large-scale application of YBa2Cu3O7-x (YBCO)-coated conductors. The three different buffer architectures were cerium oxide (CeO2), yttria-stabilized zirconia (YSZ)/CeO2, and CeO2/YSZ/CeO2. The microstructure and surface morphology of the LZO film were studied by X-ray diffraction, optical microscopy, field emission scanning electron microscopy, and atomic force microscopy. The LZO films prepared on the CeO2, YSZ/CeO2, and CeO2/YSZ/CeO2 buffer architectures were preferentially c-axis-oriented and highly textured. The in-plane texture of LZO film on CeO2 single-buffer architecture was ∆ φ = 5.5° and the out-of-plane texture was ∆ ω = 3.4°. All the LZO films had very smooth surfaces, but LZO films grown on YSZ/CeO2 and CeO2/YSZ/CeO2 buffer architectures had cracks. The highly textured LZO film grown on CeO2-seed buffered NiW tape was suitable for the epitaxial growth of YBCO film with high currents.

No MeSH data available.