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Deposition of Gd2Zr2O7 single buffer layers with different thickness for YBa2Cu3O7−δ coated conductors on metallic substrates
Physica C 470 (2010) 543–546
Contents lists available at ScienceDirect
Physica C journal homepage: www.elsevier.com/locate/physc
Deposition of Gd2Zr2O7 single buffer layers with different thickness for YBa2Cu3O7d coated conductors on metallic substrates L.L. Ying a, F. Fan a, B. Gao a, Y.M. Lu a, Z.Y. Liu a, C.B. Cai a,*, R. Hühne b, B. Holzapfel b a b
Research Center for Superconductors and Applied Technologies, Physics Department, Shanghai University, Shanghai 200444, China IFW Dresden, Helmholtzstrasse 20, 01069 Dresden, Germany
a r t i c l e
i n f o
Article history: Received 19 March 2010 Received in revised form 26 April 2010 Accepted 28 April 2010 Available online 4 May 2010 Keywords: Coated conductors Single buffer PLD Metallic substrates Biaxial texture
a b s t r a c t A series of Gd2Zr2O7 (GZO) single buffer layers with different thicknesses were epitaxially grown on highly textured Ni–5 at.% W tapes using pulsed laser deposition. These allow the subsequent growth of high-quality superconducting YBa2Cu3O7d layers. The superconducting transition temperature Tc reaches a maximum value of 92.4 K as well as a narrow transition width of 0.8 K for the optimized GZO layer thickness. The inductive measurements show the critical current density as high as 1.2 MA/ cm2 at 77 K in self-field, indicating that a GZO single buffer layer is a suitable alternative for simplifying the second generation high Tc superconducting coated conductors architecture. Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction The preparation and development of REBa2Cu3O7d (REBCO, RE = Y, Nd, Sm, etc. rare earths) coated conductors requires the application of biaxially textured substrates and buffer layers. Three main technologies have been used to obtain such biaxially textured YBCO films on metallic substrates, including Ion Beam Assisted Deposition (IBAD), Inclined Substrate Deposition (ISD), and Rolling Assisted Biaxially Textured Substrate (RABiTS). Among them the RABiTS approach is mostly attractive due to the availability of long textured substrates, the feasibility of controlled buffer growth and the potential for cost-effective processing such as chemical solution deposition for all functional layers [1]. One focus of the recent RABiTS-based coated conductor development is to realise suitable and simple buffer architectures on the metallic template. It is well known that the main function of the buffer layers is to act as a chemical barrier preventing diffusion of metallic elements into YBCO and suppressing the uncontrolled oxidation of the metallic substrate under strong oxygen atmosphere during YBCO processing, as well as to transfer the texture from the substrate to the superconducting layer. Typically, a combination of several oxides materials is used in such buffer architectures. At present, the most popular buffer system is a trilayer such as CeO2/YSZ/Y2O3 if physical vapour deposition is applied on RABiTS [2–4]. In general, such multilayer * Corresponding author. Tel.: +86 (0)21 66135019; fax: +86 (0)21 66134208. E-mail address: [email protected] (C.B. Cai). 0921-4534/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2010.04.014
architectures significantly increase the complexity as well as the cost of production. Therefore, it is of great interest to develop a simplified architecture such as a single buffer layer. We recently investigated into several oxides with a pyrochlore structure, and showed that La2Zr2O7 (LZO) is a suitable candidate for such a simplified buffer architecture [5,6]. In the present paper, we focus on the application of the isostructural Gd2Zr2O7 (GZO) as single buffer layer. GZO has a lattice parameter of a = 10.52 Å, i.e., one-quarter of the face diagonal of the pyrochlore cell is 3.72 Å, giving a good lattice match with both YBCO (a = 3.83 Å and b = 3.88 Å) and Ni (3.52 Å). It should be noted that this material is also used as a buffer layer in the IBAD approach for coated conductors [7–9]. Furthermore, GZO films prepared by chemical solution deposition [10–12] or electrodeposition [13] were tested in combination with CeO2, Y2O3 or Gd2O3 layers on Ni–W RABiTS tapes. Here, we studied the epitaxial growth of GZO buffers prepared by pulsed laser deposition, to check the suitability of GZO as single buffer layer on highly textured Ni–5% W tapes. Therefore, GZO layer having different thicknesses were prepared on the textured tape and covered afterwards with a 300 nm thick YBCO layer to study the influence of the buffer layer thickness on the superconducting properties. 2. Experimental Highly textured Ni–5 at.% W (Ni–5W) RABiTS tapes [14] were used as substrates for a subsequent deposition of a GZO buffer
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and superconducting YBCO layers. Both layers were prepared using pulsed laser deposition similar to the procedure reported previously for LZO [5,6]. The initial deposition of GZO buffer layers was performed at 750 °C in forming gas (5% H2 in Ar) at a pressure of 3.6 102 mbar to avoid NiO formation. Subsequently, more GZO was deposited in an oxygen atmosphere at a pressure of 3.3 104 mbar. The procedure described above leads to an overall deposition rate of roughly 0.05 nm GZO per pulse. Afterwards, YBCO layers were deposited at a heater temperature of 810 °C with a background pressure of 0.3 mbar O2, which were loaded with oxygen at 400 mbar during cool down. More details can be found elsewhere [3]. X-ray diffraction (XRD) h–2h scans (Co Ka) and pole figures (Cu Ka) were measured to evaluate the structure and texture of the grown films. The critical temperature Tc was determined by the temperature dependence of resistance using a Quantum Design PPMS system with a standard four-probe method. The critical current density Jc of the YBCO coated conductors was examined by inductive measurements at 77 K in self-field. 3. Results and discussion To explore the suitability of a single GZO buffer, a series of GZO/ YBCO samples were prepared on Ni–5W substrates. The YBCO thickness was fixed to 300 nm, whereas the GZO thickness was varied between 140 nm and 710 nm, according to the applied laser pulse numbers. Fig. 1 shows the h–2h X-ray diffraction patterns of samples having a different buffer thickness. The measurements reveal a high intensity of the GZO (0 0 4) peak for all films, while a low GZO (2 2 2) peak is visible as well, which is more pronounced for the samples with a thickness of 240 nm and 310 nm. For superconducting YBCO layers only (0 0 ‘) reflections were detected, indicating that all films are predominantly c-axis oriented. This is a first indication that YBCO grows epitaxially on GZO-buffered Ni– W and that the (1 1 1)-oriented grains in the GZO layer are nucleated at the interface to the substrate but are overgrown by the desired (0 0 ‘) orientation. A similar behavior was observed for Y2O3 seed layers on RABiTS [3]. In addition, small peaks of partially
textured NiO and NiWO4 layers are visible in the diffraction pattern, which are typically formed at the substrate/buffer interface during the preparation of YBCO in a high oxygen atmosphere. Pole figure measurements were performed to investigate the epitaxial growth in more detail. The results for the sample with a GZO thickness of 310 nm are exemplarily shown in Fig. 2. A strong cube texture in the GZO layer was measured for all samples with an epitaxial relationship of (0 0 1)h1 1 0iGZO || (0 0 1)h1 0 0iNi. Only in the sample with the GZO thickness of 240 nm, a minor additional (1 1 1)-oriented texture component was observed. The inplane full width at half-maximum value (FWHM) measured on XRD phi-scans of the GZO (2 2 2) peak decreases with increasing buffer thickness, reaching a value of 5.9° for the sample with 310 nm GZO (Fig. 2a), which is a significant improvement compared to the value of 7.0° ± 0.3° for Ni–5W. This texture spread stays almost constant to thicker buffers. The improvement of texture with thickness might be due to strain relaxation of the GZO with increasing distance from the layer/substrate interface. The (1 0 3) pole figures of the subsequent YBCO layer revealed a pure biaxial texture for all samples as shown exemplarily in Fig. 2b for the film on 310 nm GZO. An epitaxial relationship of (0 0 1)h1 1 0iGZO || (0 0 1)h1 0 0iYBCO was determined similar to samples grown on LZO due to the best lattice mismatch in this configuration. The in-plane FWHM of YBCO (1 0 3) was further improved and reached a value of 4.8° on the sample with a 310 nm thick GZO layer. Finally, the superconducting properties were determined on unpatterned samples. Fig. 3 shows the superconducting transition temperature Tc measured resistively on YBCO coated conductors with single GZO buffer of various thicknesses. It is found that the measured Tc increases and the transition width DTc decreases with increasing buffer thickness up to a value of 310 nm. This might be explained with the fact that too thin buffer layers are insufficient to prevent Ni diffusion, leading to a degradation of the superconducting properties in YBCO. The superconducting transition temperature Tc reaches a maximum value of 92.4 K with a very narrow transition width of 0.8 K for the sample with a GZO thickness of 310 nm. For thicker GZO layers, however, a slight reduction in Tc
Fig. 1. X-ray h–2h diffraction pattern for 300 nm thick YBCO layers deposited on Ni–5W tapes using different GZO buffer thicknesses.
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Fig. 4. Inductive Jc measurements (77 K, self-field) for YBCO layers prepared on GZO-buffered Ni–5W tapes with different buffer thickness.
The critical current density of the superconducting layer was determined by an inductive measurement technique at 77 K in self-field. With increasing GZO thickness higher Jc values were obtained for YBCO layer, indicating that a sufficient buffer thickness is necessary for such simple coated conductor architecture. The highest Jc value with 1.17 MA/cm2 was measured for the YBCO/ GZO (310 nm)/Ni–5W sample as shown in Fig. 4. This is a significant improvement compared to the values obtained for single PLD-grown LZO buffers [6]. A further increase of the buffer thickness showed a significant reduction of the critical current density which might be connected to changes in the local microstructure and needs further investigation. It is concluded that the proper selection of the GZO thickness is required to ensure best superconducting properties. Fig. 2. Phi-scans and pole figures for: (a) the GZO (2 2 2) and (b) the YBCO (1 0 3) planes, respectively, measured on a Ni–5W/GZO/YBCO sample with a buffer thickness of 310 nm.
4. Conclusions We have investigated the epitaxial growth and the thickness effect of single GZO buffers prepared by PLD on Ni–5W metallic substrates for YBCO coated conductors. As a result, highly textured YBCO layers were successfully grown on these substrates. The superconducting critical temperature as well as the critical current density improves as the GZO thickness increases from about 140 nm to 310 nm. A degradation of the superconducting properties is observed, if the GZO thickness is further increased to 710 nm, which is probably due to changes in the microstructure and needs further investigation. The Tc and Jc values of YBCO layers reach 92.4 K and 1.17 MA/cm2 (77 K, self-field), respectively, for a 310 nm thick GZO buffer, implying that YBCO coated conductors using a single GZO buffer are comparable to complex trilayer buffer architectures such as CeO2/YSZ/Y2O3, or a bilayer buffer architecture as CeO2/LZO. Thus, the present work shows a promising route to simplify the architecture and thereby to cut down the processing cost for the second generation coated conductors. Acknowledgments
Fig. 3. Superconducting transitions for YBCO layers on Ni–5W substrates using different GZO buffer thicknesses determined by resistive measurements.
was observed, which might be connected to a slightly broader inplane distribution or changes in the microstructure for thicker buffers.
The authors would like to thank M. Kühnel for technical assistance and evico GmbH for the provision of the Ni–5W tape. This work is partly sponsored by the National Natural Science Foundation of China (Nos. 50702033 and 10774098), the Ministry of Science and Technology of China (973 Projects, No. 2006CB601005, and 863 Projects, No. 2009AA03Z204), the Science and Technology Commission of Shanghai Municipality (No. 08521101502), Shang-
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hai Leading Academic Discipline Project (No. S30105), the Project Based Personnel Exchange Programme with China and Germany (PPP) (No. [2006] 3139) and the EU-FP6 Research Project ‘NanoEngineered Superconductors for Power Applications’ (NESPA No. MRTN-CT-2006-035619). References [1] A. Goyal, M.P. Paranthaman, U. Schoop, MRS Bull. 29 (2004) 552. [2] P.N. Barnes, R.M. Nekkanti, T.J. Haugan, T.A. Campbell, N.A. Yust, J.M. Evans, Supercond. Sci. Technol. 17 (2004) 957. [3] R. Hühne, V. Subramanya Sarma, D. Okai, T. Thersleff, L. Schultz, B. Holzapfel, Supercond. Sci. Technol. 20 (2007) 709. [4] M. Parans Paranthaman, S. Sathyamurthy, M.S. Bhuiyan, A. Goyal, T. Kodenkandath, X. Li, W. Zhang, C.L.H. Thieme, U. Schoop, D.T. Verebelyi, M.W. Rupich, IEEE Trans. Appl. Supercond. 15 (2005) 2632.
[5] L.L. Ying, Z.Y. Liu, Y.M. Lu, B. Gao, F. Fan, J.L. Liu, C.B. Cai, T. Thersleff, S. Engel, R. Hühne, B. Holzapfel, Physica C 469 (2009) 288. [6] L.L. Ying, Y.M. Lu, Z.Y. Liu, F. Fan, B. Gao, C.B. Cai, T. Thersleff, E. Reich, R. Hühne, B. Holzapfel, Supercond. Sci. Technol. 22 (2009) 095005. [7] H. Kutami, T. Hayashida, S. Hanyu, C. Tashita, M. Igarashi, H. Fuji, Y. Hanada, K. Kakimoto, Y. Iijima, T. Saitoh, Physica C 469 (2009) 1290. [8] Y. Iijima, N. Tanabe, O. Kohno, Y. Ikeno, Appl. Phys. Lett. 60 (1992) 769. [9] Y. Iijima, K. Kakimoto, Y. Yamada, T. Izumi, T. Saitoh, Y. Shiohara, MRS Bull. 29 (2004) 564. [10] T. Aytug et al., J. Mater. Res. 20 (2005) 2988. [11] Y.X. Zhou, X. Zhang, H. Fang, P.T. Putman, K. Salama, IEEE Trans. Appl. Supercond. 15 (2005) 2711. [12] M. Paranthaman, T. Aytug, K. Kim, E.D. Specht, L. Heatherly, IEEE Trans. Appl. Supercond. 19 (2009) 3303. [13] R. Bhattacharya, S. Phok, W. Zhao, A. Norman, IEEE Trans. Appl. Supercond. 19 (2009) 3451. [14] J. Eickemeyer, D. Selbmann, R. Opitz, B. de Boer, B. Holzapfel, L. Schultz, U. Miller, Supercond. Sci. Technol. 14 (2001) 152.
Contents lists available at ScienceDirect
Physica C journal homepage: www.elsevier.com/locate/physc
Deposition of Gd2Zr2O7 single buffer layers with different thickness for YBa2Cu3O7d coated conductors on metallic substrates L.L. Ying a, F. Fan a, B. Gao a, Y.M. Lu a, Z.Y. Liu a, C.B. Cai a,*, R. Hühne b, B. Holzapfel b a b
Research Center for Superconductors and Applied Technologies, Physics Department, Shanghai University, Shanghai 200444, China IFW Dresden, Helmholtzstrasse 20, 01069 Dresden, Germany
a r t i c l e
i n f o
Article history: Received 19 March 2010 Received in revised form 26 April 2010 Accepted 28 April 2010 Available online 4 May 2010 Keywords: Coated conductors Single buffer PLD Metallic substrates Biaxial texture
a b s t r a c t A series of Gd2Zr2O7 (GZO) single buffer layers with different thicknesses were epitaxially grown on highly textured Ni–5 at.% W tapes using pulsed laser deposition. These allow the subsequent growth of high-quality superconducting YBa2Cu3O7d layers. The superconducting transition temperature Tc reaches a maximum value of 92.4 K as well as a narrow transition width of 0.8 K for the optimized GZO layer thickness. The inductive measurements show the critical current density as high as 1.2 MA/ cm2 at 77 K in self-field, indicating that a GZO single buffer layer is a suitable alternative for simplifying the second generation high Tc superconducting coated conductors architecture. Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction The preparation and development of REBa2Cu3O7d (REBCO, RE = Y, Nd, Sm, etc. rare earths) coated conductors requires the application of biaxially textured substrates and buffer layers. Three main technologies have been used to obtain such biaxially textured YBCO films on metallic substrates, including Ion Beam Assisted Deposition (IBAD), Inclined Substrate Deposition (ISD), and Rolling Assisted Biaxially Textured Substrate (RABiTS). Among them the RABiTS approach is mostly attractive due to the availability of long textured substrates, the feasibility of controlled buffer growth and the potential for cost-effective processing such as chemical solution deposition for all functional layers [1]. One focus of the recent RABiTS-based coated conductor development is to realise suitable and simple buffer architectures on the metallic template. It is well known that the main function of the buffer layers is to act as a chemical barrier preventing diffusion of metallic elements into YBCO and suppressing the uncontrolled oxidation of the metallic substrate under strong oxygen atmosphere during YBCO processing, as well as to transfer the texture from the substrate to the superconducting layer. Typically, a combination of several oxides materials is used in such buffer architectures. At present, the most popular buffer system is a trilayer such as CeO2/YSZ/Y2O3 if physical vapour deposition is applied on RABiTS [2–4]. In general, such multilayer * Corresponding author. Tel.: +86 (0)21 66135019; fax: +86 (0)21 66134208. E-mail address: [email protected] (C.B. Cai). 0921-4534/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2010.04.014
architectures significantly increase the complexity as well as the cost of production. Therefore, it is of great interest to develop a simplified architecture such as a single buffer layer. We recently investigated into several oxides with a pyrochlore structure, and showed that La2Zr2O7 (LZO) is a suitable candidate for such a simplified buffer architecture [5,6]. In the present paper, we focus on the application of the isostructural Gd2Zr2O7 (GZO) as single buffer layer. GZO has a lattice parameter of a = 10.52 Å, i.e., one-quarter of the face diagonal of the pyrochlore cell is 3.72 Å, giving a good lattice match with both YBCO (a = 3.83 Å and b = 3.88 Å) and Ni (3.52 Å). It should be noted that this material is also used as a buffer layer in the IBAD approach for coated conductors [7–9]. Furthermore, GZO films prepared by chemical solution deposition [10–12] or electrodeposition [13] were tested in combination with CeO2, Y2O3 or Gd2O3 layers on Ni–W RABiTS tapes. Here, we studied the epitaxial growth of GZO buffers prepared by pulsed laser deposition, to check the suitability of GZO as single buffer layer on highly textured Ni–5% W tapes. Therefore, GZO layer having different thicknesses were prepared on the textured tape and covered afterwards with a 300 nm thick YBCO layer to study the influence of the buffer layer thickness on the superconducting properties. 2. Experimental Highly textured Ni–5 at.% W (Ni–5W) RABiTS tapes [14] were used as substrates for a subsequent deposition of a GZO buffer
544
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and superconducting YBCO layers. Both layers were prepared using pulsed laser deposition similar to the procedure reported previously for LZO [5,6]. The initial deposition of GZO buffer layers was performed at 750 °C in forming gas (5% H2 in Ar) at a pressure of 3.6 102 mbar to avoid NiO formation. Subsequently, more GZO was deposited in an oxygen atmosphere at a pressure of 3.3 104 mbar. The procedure described above leads to an overall deposition rate of roughly 0.05 nm GZO per pulse. Afterwards, YBCO layers were deposited at a heater temperature of 810 °C with a background pressure of 0.3 mbar O2, which were loaded with oxygen at 400 mbar during cool down. More details can be found elsewhere [3]. X-ray diffraction (XRD) h–2h scans (Co Ka) and pole figures (Cu Ka) were measured to evaluate the structure and texture of the grown films. The critical temperature Tc was determined by the temperature dependence of resistance using a Quantum Design PPMS system with a standard four-probe method. The critical current density Jc of the YBCO coated conductors was examined by inductive measurements at 77 K in self-field. 3. Results and discussion To explore the suitability of a single GZO buffer, a series of GZO/ YBCO samples were prepared on Ni–5W substrates. The YBCO thickness was fixed to 300 nm, whereas the GZO thickness was varied between 140 nm and 710 nm, according to the applied laser pulse numbers. Fig. 1 shows the h–2h X-ray diffraction patterns of samples having a different buffer thickness. The measurements reveal a high intensity of the GZO (0 0 4) peak for all films, while a low GZO (2 2 2) peak is visible as well, which is more pronounced for the samples with a thickness of 240 nm and 310 nm. For superconducting YBCO layers only (0 0 ‘) reflections were detected, indicating that all films are predominantly c-axis oriented. This is a first indication that YBCO grows epitaxially on GZO-buffered Ni– W and that the (1 1 1)-oriented grains in the GZO layer are nucleated at the interface to the substrate but are overgrown by the desired (0 0 ‘) orientation. A similar behavior was observed for Y2O3 seed layers on RABiTS [3]. In addition, small peaks of partially
textured NiO and NiWO4 layers are visible in the diffraction pattern, which are typically formed at the substrate/buffer interface during the preparation of YBCO in a high oxygen atmosphere. Pole figure measurements were performed to investigate the epitaxial growth in more detail. The results for the sample with a GZO thickness of 310 nm are exemplarily shown in Fig. 2. A strong cube texture in the GZO layer was measured for all samples with an epitaxial relationship of (0 0 1)h1 1 0iGZO || (0 0 1)h1 0 0iNi. Only in the sample with the GZO thickness of 240 nm, a minor additional (1 1 1)-oriented texture component was observed. The inplane full width at half-maximum value (FWHM) measured on XRD phi-scans of the GZO (2 2 2) peak decreases with increasing buffer thickness, reaching a value of 5.9° for the sample with 310 nm GZO (Fig. 2a), which is a significant improvement compared to the value of 7.0° ± 0.3° for Ni–5W. This texture spread stays almost constant to thicker buffers. The improvement of texture with thickness might be due to strain relaxation of the GZO with increasing distance from the layer/substrate interface. The (1 0 3) pole figures of the subsequent YBCO layer revealed a pure biaxial texture for all samples as shown exemplarily in Fig. 2b for the film on 310 nm GZO. An epitaxial relationship of (0 0 1)h1 1 0iGZO || (0 0 1)h1 0 0iYBCO was determined similar to samples grown on LZO due to the best lattice mismatch in this configuration. The in-plane FWHM of YBCO (1 0 3) was further improved and reached a value of 4.8° on the sample with a 310 nm thick GZO layer. Finally, the superconducting properties were determined on unpatterned samples. Fig. 3 shows the superconducting transition temperature Tc measured resistively on YBCO coated conductors with single GZO buffer of various thicknesses. It is found that the measured Tc increases and the transition width DTc decreases with increasing buffer thickness up to a value of 310 nm. This might be explained with the fact that too thin buffer layers are insufficient to prevent Ni diffusion, leading to a degradation of the superconducting properties in YBCO. The superconducting transition temperature Tc reaches a maximum value of 92.4 K with a very narrow transition width of 0.8 K for the sample with a GZO thickness of 310 nm. For thicker GZO layers, however, a slight reduction in Tc
Fig. 1. X-ray h–2h diffraction pattern for 300 nm thick YBCO layers deposited on Ni–5W tapes using different GZO buffer thicknesses.
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Fig. 4. Inductive Jc measurements (77 K, self-field) for YBCO layers prepared on GZO-buffered Ni–5W tapes with different buffer thickness.
The critical current density of the superconducting layer was determined by an inductive measurement technique at 77 K in self-field. With increasing GZO thickness higher Jc values were obtained for YBCO layer, indicating that a sufficient buffer thickness is necessary for such simple coated conductor architecture. The highest Jc value with 1.17 MA/cm2 was measured for the YBCO/ GZO (310 nm)/Ni–5W sample as shown in Fig. 4. This is a significant improvement compared to the values obtained for single PLD-grown LZO buffers [6]. A further increase of the buffer thickness showed a significant reduction of the critical current density which might be connected to changes in the local microstructure and needs further investigation. It is concluded that the proper selection of the GZO thickness is required to ensure best superconducting properties. Fig. 2. Phi-scans and pole figures for: (a) the GZO (2 2 2) and (b) the YBCO (1 0 3) planes, respectively, measured on a Ni–5W/GZO/YBCO sample with a buffer thickness of 310 nm.
4. Conclusions We have investigated the epitaxial growth and the thickness effect of single GZO buffers prepared by PLD on Ni–5W metallic substrates for YBCO coated conductors. As a result, highly textured YBCO layers were successfully grown on these substrates. The superconducting critical temperature as well as the critical current density improves as the GZO thickness increases from about 140 nm to 310 nm. A degradation of the superconducting properties is observed, if the GZO thickness is further increased to 710 nm, which is probably due to changes in the microstructure and needs further investigation. The Tc and Jc values of YBCO layers reach 92.4 K and 1.17 MA/cm2 (77 K, self-field), respectively, for a 310 nm thick GZO buffer, implying that YBCO coated conductors using a single GZO buffer are comparable to complex trilayer buffer architectures such as CeO2/YSZ/Y2O3, or a bilayer buffer architecture as CeO2/LZO. Thus, the present work shows a promising route to simplify the architecture and thereby to cut down the processing cost for the second generation coated conductors. Acknowledgments
Fig. 3. Superconducting transitions for YBCO layers on Ni–5W substrates using different GZO buffer thicknesses determined by resistive measurements.
was observed, which might be connected to a slightly broader inplane distribution or changes in the microstructure for thicker buffers.
The authors would like to thank M. Kühnel for technical assistance and evico GmbH for the provision of the Ni–5W tape. This work is partly sponsored by the National Natural Science Foundation of China (Nos. 50702033 and 10774098), the Ministry of Science and Technology of China (973 Projects, No. 2006CB601005, and 863 Projects, No. 2009AA03Z204), the Science and Technology Commission of Shanghai Municipality (No. 08521101502), Shang-
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hai Leading Academic Discipline Project (No. S30105), the Project Based Personnel Exchange Programme with China and Germany (PPP) (No. [2006] 3139) and the EU-FP6 Research Project ‘NanoEngineered Superconductors for Power Applications’ (NESPA No. MRTN-CT-2006-035619). References [1] A. Goyal, M.P. Paranthaman, U. Schoop, MRS Bull. 29 (2004) 552. [2] P.N. Barnes, R.M. Nekkanti, T.J. Haugan, T.A. Campbell, N.A. Yust, J.M. Evans, Supercond. Sci. Technol. 17 (2004) 957. [3] R. Hühne, V. Subramanya Sarma, D. Okai, T. Thersleff, L. Schultz, B. Holzapfel, Supercond. Sci. Technol. 20 (2007) 709. [4] M. Parans Paranthaman, S. Sathyamurthy, M.S. Bhuiyan, A. Goyal, T. Kodenkandath, X. Li, W. Zhang, C.L.H. Thieme, U. Schoop, D.T. Verebelyi, M.W. Rupich, IEEE Trans. Appl. Supercond. 15 (2005) 2632.
[5] L.L. Ying, Z.Y. Liu, Y.M. Lu, B. Gao, F. Fan, J.L. Liu, C.B. Cai, T. Thersleff, S. Engel, R. Hühne, B. Holzapfel, Physica C 469 (2009) 288. [6] L.L. Ying, Y.M. Lu, Z.Y. Liu, F. Fan, B. Gao, C.B. Cai, T. Thersleff, E. Reich, R. Hühne, B. Holzapfel, Supercond. Sci. Technol. 22 (2009) 095005. [7] H. Kutami, T. Hayashida, S. Hanyu, C. Tashita, M. Igarashi, H. Fuji, Y. Hanada, K. Kakimoto, Y. Iijima, T. Saitoh, Physica C 469 (2009) 1290. [8] Y. Iijima, N. Tanabe, O. Kohno, Y. Ikeno, Appl. Phys. Lett. 60 (1992) 769. [9] Y. Iijima, K. Kakimoto, Y. Yamada, T. Izumi, T. Saitoh, Y. Shiohara, MRS Bull. 29 (2004) 564. [10] T. Aytug et al., J. Mater. Res. 20 (2005) 2988. [11] Y.X. Zhou, X. Zhang, H. Fang, P.T. Putman, K. Salama, IEEE Trans. Appl. Supercond. 15 (2005) 2711. [12] M. Paranthaman, T. Aytug, K. Kim, E.D. Specht, L. Heatherly, IEEE Trans. Appl. Supercond. 19 (2009) 3303. [13] R. Bhattacharya, S. Phok, W. Zhao, A. Norman, IEEE Trans. Appl. Supercond. 19 (2009) 3451. [14] J. Eickemeyer, D. Selbmann, R. Opitz, B. de Boer, B. Holzapfel, L. Schultz, U. Miller, Supercond. Sci. Technol. 14 (2001) 152.