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Epitaxial thick film of YBCO by high temperature spray pyrolysis for coated conductors
Physica C 386 (2003) 296–299 www.elsevier.com/locate/physc
Epitaxial thick film of YBCO by high temperature spray pyrolysis for coated conductors Z. Supardi a,b, G. Delabouglise a, C. Peroz c, A. Sin a, C. Villard c, P. Odier d,*, F. Weiss a a LMGP-INPG, 38406 Saint Martin d’H eres Cedex, France Department of Physics, Universitas Negeri Surabaya, 60254 Surabaya, Indonesia c CRETA, BP166, 38042 Grenoble Cedex 09, France Laboratoire de Cristallographie, CNRS, BP166, 38042 Grenoble Cedex 09, France
b
d
Abstract YBCO thick films have been synthesized using a low cost spray pyrolysis method. We used an all nitrate precursor approach to grow epitaxial HTS oxide film on SrTiO3 (0 0 1) substrate at a high deposition rate and at high temperature (over 800 °C). In these experiments thick YBCO films (lm) were grown in situ at 850 °C within 4 min; the final sintering process is performed at the same temperature for 2 h under oxygen atmosphere before low temperature oxygen loading. X-ray diffraction results (h–2h scans and u scans) show that the films have not only a strong c-axis texture (mis-orientation 0.4°) but also a sharp in-plane biaxial orientation (mis-orientation is 1.4°). The critical temperature (Tc ) was 91 K and the critical current density (Jc ) higher than 1:4 106 A/cm2 (at 77 K, 0 T), while film thickness is over 1 lm. Spray pyrolysis is a promising technique for coated conductors. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 74.76.Bz Keywords: YBCO; Spray pyrolysis; Epitaxial film
1. Introduction YBa2 Cu3 O7y (YBCO) has been identified as one of the most promising candidate for electrical engineering applications at 77 K of high-temperature-superconductor (HTS). YBCO based coated conductors have a strong pinning in magnetic field, high Jc in a thin film form, good mechanical flexibility, low AC losses factor, and their pro-
*
Corresponding author. Tel.: +33-4-76-88-10-45; fax: +33-476-88-10-38. E-mail address: [email protected] (P. Odier).
duction can be scaled up to long lengths with low cost [1]. The grain boundaries in YBCO, usually act as weak-links that can depress the attainable Jc far below the intrinsic value. To overcome this problem, a highly textured crystalline state is required. One of the non-vacuum synthesis methods, which can be used to obtain epitaxial YBCO thick films, is Spray Pyrolysis [2–5]. It has been shown to be simple, inexpensive, with a high deposition rate (over 0.1 lm/min), and a precise control of processing parameters such as thickness [6]. Also it offers a molecular level mixing of the constituents leading to an excellent chemical homogeneity and
0921-4534/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0921-4534(02)02138-X
Z. Supardi et al. / Physica C 386 (2003) 296–299
297
composition control, all treatments can be made in situ, on line! Finally, this method supports ‘‘green’’ technology and has been used successfully for the synthesis of other HTS films, such as HBCCO and TBCCO [7,8].
2. Experimental In the present experiments we used a reactor set up that is described elsewhere [9]. The precursor solution is prepared from raw pure compounds (99.9%): Y2 O3 , BaCO3 , and CuO. These compounds were dissolved in appropriate atomic ratio in diluted nitric acid, on a hot magnetic stirrer, in order to reach the final molarity of 0.3 mol/l. The films were deposited at 850 °C during 4 min. The sprayed solution was transported to the deposition zone with an argon flow of 3 l/min and decomposed on the hot substrate. This deposition was followed by in situ heat treatments: sintering in oxygen at 850 °C during 120 min, cooling to 525 °C and annealing at this temperature for 60 min. The crystalline structure and texture of YBCO films were characterized by X-ray diffraction (XRD) (h=2h, x and u scans). Surface morphology was analyzed by scanning electron microscopy (SEM). Film cross sections were analyzed by transmission electron microscopy (TEM). The superconducting properties Jc and Tc were measured by AC susceptibility method and transport measurements. Critical current profiles in magnetic field were analyzed by Hall probe mapping.
3. Results and discussion 3.1. Stoichiometry of the precursor solution, phase purity and texture formation The first step in high temperature deposition of YBCO is to adjust the stoichiometry in the starting solution to get films with the right cationic ratio, Y:Ba:Cu ffi 1:2:3. For nitrate precursors, the sticking coefficient is different for Y, Ba, and Cu and temperature dependent, then the stoichiometry needs adjustments [10]. In these experiments, the precursor ratio was Y:Ba:Cu ¼ 1:00:2.65:1.35 for
Fig. 1. In-plane epitaxy (Du) of YBCO film on SrTiO3 .
deposition on SrTiO3 substrates at 850 °C. This ratio is close to that used by others [4,5]. In these conditions YBCO films can be grown on single crystalline substrates not only with a good c-axis fiber texture but also with an excellent biaxial texture. The rocking curve on the YBCO (0 0 5) diffraction line showed an excellent degree of c-axis alignment, i.e. FWHM ¼ 0:4°. By u scan on the YBCO (1 0 2), we obtained FWHM 1:4° showing an excellent in-plane epitaxy, see Fig. 1. Fig. 2 shows SEM for film having high structural and superconducting properties. This film has a good grain connectivity and homogeneous grain size in the range of 5 lm. However secondary phase (CuO excess) are observed on the surface, pores are also present on the surface and in the bulk (TEM). These defects do not have a serious effect on the superconducting properties of the films. TEM analyses, see Fig. 3, show a good crystallinity of the film over its thickness, i.e. 1 lm. Also the films have a sharp interface and long range ordering of Y/Ba atoms. Some mis-oriented grains (a-axis) were also detected. 3.2. Superconducting properties Fig. 4 shows Tc , Jc , and a critical current map of an optimized YBCO film. It had Tc 91 K with DTc ffi 1 K and Jc 1:4 MA/cm2 at 77 K and 0 T (by AC susceptibility). Furthermore, the critical
298
Z. Supardi et al. / Physica C 386 (2003) 296–299
current map shows definitively well connected grains around the film, but also inhomogeneities on a longer grain distance (2000 lm). Jc values calculated for this film (1 lm thick) is 1.1 MA/cm2 for the average, while local Jc Õs can be as high as 3.6 MA/cm2 . Conversely to most publications in this field [4,5], we used rather concentrated solution, we believe this is the key for obtaining such high properties [11] and due to an appropriate local conditions permitting high quality epitaxial growth of YBCO thick films. Fig. 2. SEM photograph of YBCO film on SrTiO3 .
4. Conclusion Spray pyrolysis is a very promising method for getting epitaxial YBCO thick film with high current performance (Jc > 1 MA/cm2 ) using very low cost equipment and ‘‘green’’ raw materials. The high rate deposition (0.25 lm/min) encourages very much to attempt scaling up of this process for producing long length-coated conductors in the future.
Acknowledgements
Fig. 3. TEM photograph of YBCO film on SrTiO3 .
The authors are pleased to thank Supertext Project (BRPR-CT97-0556) and Rh^ one-Alpes Region (Fr) for financial support, Dr. Garry Perkin for magnetic measurements at Imperial College (UK) and Department of Inorganic Chemistry at University Complutense Madrid (Sp) for TEM analysis.
References
Fig. 4. Tc , Jc and critical current map of YBCO film on SrTiO3 .
[1] Y. Iijima, K. Matsumoto, Supercond. Sci. Technol. 13 (2000) 68. [2] M. Jergel, Supercond. Sci. Technol. 8 (1995) 67. [3] M. Jergel, S. Chromik, V. Strbik, V. Smatko, F. Hanik, G. Plesch, S. Buchta, Valtyniova, Supercond. Sci. Technol. 5 (1992) 225. [4] M.-D. MacManus-Driscoll, A. Ferreri, J.J. Well, J.G.A. Nelstrop, Supercond. Sci. Technol. 14 (2001) 96. [5] T.C. Shields, K. Kawano, T.W. Button, J.S. Abell, Supercond. Sci. Technol. 15 (2002) 99.
Z. Supardi et al. / Physica C 386 (2003) 296–299 [6] Z. Supardi, A. Sin, F. Weiss, P. Odier, in: Proceedings of the 5th Indonesian Students Scientific Meeting, 6–7 October, Paris, France, 2000, pp. 200–203. [7] A. Sin, Z. Supardi, P. Odier, F. Weiss, M. NunezRegueiro, Supercond. Sci. Technol. 13 (2000) 617. [8] A. Phok, Ph. Galez, J.L. Jorda, Z. Supardi, D. De Barros, P. Odier, A. Sin, F. Weiss, Physica C 372 (2002) 876.
299
[9] Z. Supardi, G. Delabouglise, P. Odier, C. Peroz, A. Sin, C. Villard, F. Weiss, Supercond. Sci. Technol., in preparation; Z. Supardi, PhD thesis, Grenoble, France, December 2001. [10] G.B. Blanchet, C.R. Fincher Jr., Supercond. Sci. Technol. 5 (1991) 69. [11] P. Odier, F. Weiss, Z. Supardi, pending patent Fr-0202217.
Epitaxial thick film of YBCO by high temperature spray pyrolysis for coated conductors Z. Supardi a,b, G. Delabouglise a, C. Peroz c, A. Sin a, C. Villard c, P. Odier d,*, F. Weiss a a LMGP-INPG, 38406 Saint Martin d’H eres Cedex, France Department of Physics, Universitas Negeri Surabaya, 60254 Surabaya, Indonesia c CRETA, BP166, 38042 Grenoble Cedex 09, France Laboratoire de Cristallographie, CNRS, BP166, 38042 Grenoble Cedex 09, France
b
d
Abstract YBCO thick films have been synthesized using a low cost spray pyrolysis method. We used an all nitrate precursor approach to grow epitaxial HTS oxide film on SrTiO3 (0 0 1) substrate at a high deposition rate and at high temperature (over 800 °C). In these experiments thick YBCO films (lm) were grown in situ at 850 °C within 4 min; the final sintering process is performed at the same temperature for 2 h under oxygen atmosphere before low temperature oxygen loading. X-ray diffraction results (h–2h scans and u scans) show that the films have not only a strong c-axis texture (mis-orientation 0.4°) but also a sharp in-plane biaxial orientation (mis-orientation is 1.4°). The critical temperature (Tc ) was 91 K and the critical current density (Jc ) higher than 1:4 106 A/cm2 (at 77 K, 0 T), while film thickness is over 1 lm. Spray pyrolysis is a promising technique for coated conductors. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 74.76.Bz Keywords: YBCO; Spray pyrolysis; Epitaxial film
1. Introduction YBa2 Cu3 O7y (YBCO) has been identified as one of the most promising candidate for electrical engineering applications at 77 K of high-temperature-superconductor (HTS). YBCO based coated conductors have a strong pinning in magnetic field, high Jc in a thin film form, good mechanical flexibility, low AC losses factor, and their pro-
*
Corresponding author. Tel.: +33-4-76-88-10-45; fax: +33-476-88-10-38. E-mail address: [email protected] (P. Odier).
duction can be scaled up to long lengths with low cost [1]. The grain boundaries in YBCO, usually act as weak-links that can depress the attainable Jc far below the intrinsic value. To overcome this problem, a highly textured crystalline state is required. One of the non-vacuum synthesis methods, which can be used to obtain epitaxial YBCO thick films, is Spray Pyrolysis [2–5]. It has been shown to be simple, inexpensive, with a high deposition rate (over 0.1 lm/min), and a precise control of processing parameters such as thickness [6]. Also it offers a molecular level mixing of the constituents leading to an excellent chemical homogeneity and
0921-4534/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0921-4534(02)02138-X
Z. Supardi et al. / Physica C 386 (2003) 296–299
297
composition control, all treatments can be made in situ, on line! Finally, this method supports ‘‘green’’ technology and has been used successfully for the synthesis of other HTS films, such as HBCCO and TBCCO [7,8].
2. Experimental In the present experiments we used a reactor set up that is described elsewhere [9]. The precursor solution is prepared from raw pure compounds (99.9%): Y2 O3 , BaCO3 , and CuO. These compounds were dissolved in appropriate atomic ratio in diluted nitric acid, on a hot magnetic stirrer, in order to reach the final molarity of 0.3 mol/l. The films were deposited at 850 °C during 4 min. The sprayed solution was transported to the deposition zone with an argon flow of 3 l/min and decomposed on the hot substrate. This deposition was followed by in situ heat treatments: sintering in oxygen at 850 °C during 120 min, cooling to 525 °C and annealing at this temperature for 60 min. The crystalline structure and texture of YBCO films were characterized by X-ray diffraction (XRD) (h=2h, x and u scans). Surface morphology was analyzed by scanning electron microscopy (SEM). Film cross sections were analyzed by transmission electron microscopy (TEM). The superconducting properties Jc and Tc were measured by AC susceptibility method and transport measurements. Critical current profiles in magnetic field were analyzed by Hall probe mapping.
3. Results and discussion 3.1. Stoichiometry of the precursor solution, phase purity and texture formation The first step in high temperature deposition of YBCO is to adjust the stoichiometry in the starting solution to get films with the right cationic ratio, Y:Ba:Cu ffi 1:2:3. For nitrate precursors, the sticking coefficient is different for Y, Ba, and Cu and temperature dependent, then the stoichiometry needs adjustments [10]. In these experiments, the precursor ratio was Y:Ba:Cu ¼ 1:00:2.65:1.35 for
Fig. 1. In-plane epitaxy (Du) of YBCO film on SrTiO3 .
deposition on SrTiO3 substrates at 850 °C. This ratio is close to that used by others [4,5]. In these conditions YBCO films can be grown on single crystalline substrates not only with a good c-axis fiber texture but also with an excellent biaxial texture. The rocking curve on the YBCO (0 0 5) diffraction line showed an excellent degree of c-axis alignment, i.e. FWHM ¼ 0:4°. By u scan on the YBCO (1 0 2), we obtained FWHM 1:4° showing an excellent in-plane epitaxy, see Fig. 1. Fig. 2 shows SEM for film having high structural and superconducting properties. This film has a good grain connectivity and homogeneous grain size in the range of 5 lm. However secondary phase (CuO excess) are observed on the surface, pores are also present on the surface and in the bulk (TEM). These defects do not have a serious effect on the superconducting properties of the films. TEM analyses, see Fig. 3, show a good crystallinity of the film over its thickness, i.e. 1 lm. Also the films have a sharp interface and long range ordering of Y/Ba atoms. Some mis-oriented grains (a-axis) were also detected. 3.2. Superconducting properties Fig. 4 shows Tc , Jc , and a critical current map of an optimized YBCO film. It had Tc 91 K with DTc ffi 1 K and Jc 1:4 MA/cm2 at 77 K and 0 T (by AC susceptibility). Furthermore, the critical
298
Z. Supardi et al. / Physica C 386 (2003) 296–299
current map shows definitively well connected grains around the film, but also inhomogeneities on a longer grain distance (2000 lm). Jc values calculated for this film (1 lm thick) is 1.1 MA/cm2 for the average, while local Jc Õs can be as high as 3.6 MA/cm2 . Conversely to most publications in this field [4,5], we used rather concentrated solution, we believe this is the key for obtaining such high properties [11] and due to an appropriate local conditions permitting high quality epitaxial growth of YBCO thick films. Fig. 2. SEM photograph of YBCO film on SrTiO3 .
4. Conclusion Spray pyrolysis is a very promising method for getting epitaxial YBCO thick film with high current performance (Jc > 1 MA/cm2 ) using very low cost equipment and ‘‘green’’ raw materials. The high rate deposition (0.25 lm/min) encourages very much to attempt scaling up of this process for producing long length-coated conductors in the future.
Acknowledgements
Fig. 3. TEM photograph of YBCO film on SrTiO3 .
The authors are pleased to thank Supertext Project (BRPR-CT97-0556) and Rh^ one-Alpes Region (Fr) for financial support, Dr. Garry Perkin for magnetic measurements at Imperial College (UK) and Department of Inorganic Chemistry at University Complutense Madrid (Sp) for TEM analysis.
References
Fig. 4. Tc , Jc and critical current map of YBCO film on SrTiO3 .
[1] Y. Iijima, K. Matsumoto, Supercond. Sci. Technol. 13 (2000) 68. [2] M. Jergel, Supercond. Sci. Technol. 8 (1995) 67. [3] M. Jergel, S. Chromik, V. Strbik, V. Smatko, F. Hanik, G. Plesch, S. Buchta, Valtyniova, Supercond. Sci. Technol. 5 (1992) 225. [4] M.-D. MacManus-Driscoll, A. Ferreri, J.J. Well, J.G.A. Nelstrop, Supercond. Sci. Technol. 14 (2001) 96. [5] T.C. Shields, K. Kawano, T.W. Button, J.S. Abell, Supercond. Sci. Technol. 15 (2002) 99.
Z. Supardi et al. / Physica C 386 (2003) 296–299 [6] Z. Supardi, A. Sin, F. Weiss, P. Odier, in: Proceedings of the 5th Indonesian Students Scientific Meeting, 6–7 October, Paris, France, 2000, pp. 200–203. [7] A. Sin, Z. Supardi, P. Odier, F. Weiss, M. NunezRegueiro, Supercond. Sci. Technol. 13 (2000) 617. [8] A. Phok, Ph. Galez, J.L. Jorda, Z. Supardi, D. De Barros, P. Odier, A. Sin, F. Weiss, Physica C 372 (2002) 876.
299
[9] Z. Supardi, G. Delabouglise, P. Odier, C. Peroz, A. Sin, C. Villard, F. Weiss, Supercond. Sci. Technol., in preparation; Z. Supardi, PhD thesis, Grenoble, France, December 2001. [10] G.B. Blanchet, C.R. Fincher Jr., Supercond. Sci. Technol. 5 (1991) 69. [11] P. Odier, F. Weiss, Z. Supardi, pending patent Fr-0202217.