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Processing for long YBCO coated conductors by advanced TFA-MOD process
Physica C 412–414 (2004) 916–919 www.elsevier.com/locate/physc
Processing for long YBCO coated conductors by advanced TFA-MOD process Hiroshi Fuji a,*, Tetsuji Honjo a, Ryo Teranishi a, Yoshitaka Tokunaga a, Junko Matsuda a, Shigenobu Asada a, Yutaka Yamada a, Teruo Izumi a, Yuh Shiohara a, Yasuhiro Iijima b, Takashi Saitoh b, Atsushi Kaneko c, Kiyoshi Murata c a
Superconductivity Research Laboratory, ISTEC, Shinonome 1-10-13, Koto-ku, Tokyo 135-0062, Japan b Fujikura Ltd., 1-5-1, Kiba, Koto-ku, Tokyo 135-8512, Japan c Shibaura Institute of Technology, 3-9-14, Shibaura, Minato-ku, Tokyo 108-8548, Japan Received 29 October 2003; accepted 2 February 2004 Available online 1 June 2004
Abstract The long tape process was developed using the advanced TFA precursor solution. In a long tape production, the advanced TFA precursor solution was coated by a die-coater using the reel-to-reel system, and the multi-coating method was applied for thicker film fabrication. We successfully fabricated long uniform precursor films. In the high temperature treatment, a large scale equipment for the continuous long tape process was developed. This equipment had a perpendicular gas flow system to the tape length which is effective to fabricate the uniform films. Ic values and its distribution in the YBCO tape fabricated by this method on CeO2 /IBAD-Gd2 Zr2 O7 /Hastelloy were measured. And the uniform and high performance was confirmed. A 0.25 m long YBCO film with 1.38 lm in thickness on the metal substrate shows the high Ic performance of 210 A with end to end at 77.3 K in self-fields. Ó 2004 Published by Elsevier B.V. PACS: 81.15.)z; 74.72.Bk; 81.10.Jt Keywords: TFA-MOD process; IBAD
1. Introduction The MOD process for YBa2 Cu3 O7x (Y123) using metal trifluoroacetate (TFA) precursors is
*
Corresponding author. Tel.: +81-3-3536-5711; fax: +81-33536-5705. E-mail address: [email protected] (H. Fuji). 0921-4534/$ - see front matter Ó 2004 Published by Elsevier B.V. doi:10.1016/j.physc.2004.02.206
considered to be a strong candidate as a low cost process for coated conductors, since the TFAMOD process is essentially a non vacuum process. Additionally, it has been well confirmed that this process has an advantage to provide a high Jc film of MA/cm2 class. In our previous work, it was confirmed that the combination of CeO2 by PLD on Gd2 Zr2 O7 by IBAD is effective buffer layers on a metal substrate for the TFA-MOD process. In
H. Fuji et al. / Physica C 412–414 (2004) 916–919
2. Experimental A CeO2 buffer layer was deposited on IBADGd2 Zr2 O7 /Hastelloy substrates by pulse laser deposition (PLD) method at 600 °C in about 30 mTorr O2 gas atmosphere. The deposition was carried out by the reel-to-reel system and the thickness of the CeO2 layer was controlled to be about 1.0 lm thick. In the case of the longer tape, a new TFA precursor solution [3] was coated on substrates by a die-coater using the continuous reel-to-reel system. In order to control the thickness of coated films, the traveling rate dependence of the thickness using the solutions with different viscosities were investigated. The traveling rate was changed from 10 to 40 mm/min for the solutions with the viscosities of 54 and 61 cp. The viscosity of the solution was controlled by the ratio of the salts and the solvent. The heat treatment was conducted by two stages at which are the low temperature and at the successive high temperature. In the low temperature heat treatment, the coated films were decomposed to the mixture consisted of amorphous, oxides, fluorides and oxyfluoride, etc. which is called as a precursor film using the heating rate of 5 °C/min to 400 °C in a moist O2 atmosphere. The processes of the coating
and the low temperature heat treatment were repeated several times to obtain thick precursor films. In the high temperature heat treatment, the films were traveled in a long tube furnace held at 760 °C in a forming gas of Ar and 0.1% O2 and 6.3% H2 O by the reel-to-reel system. Then, the forming gas was flowed along the perpendicular direction to the long tape. The crystallinity of the long Y123 tape was evaluated by XRD measurements and FIB SIM images. Ic performance and its distribution of these Y123 films were measured by a four-probe transport method.
3. Results and discussion Fig. 1 shows the traveling rate dependence of the thickness of the coated film for two solutions with different viscosities. Both curves revealed a liner relationship. This phenomenon is in a good agreement with the prediction by the following equation: T ¼ kðV gÞn
ð1Þ
(T : thickness; k: constant; V : traveling rate; g: viscosity of the solutions; n ¼ 1 at this study). In this study, the viscosity values of the solutions were controlled to be about 54 and 61 cp. The difference in the slopes in Fig. 1 is consistent with the difference from that in the viscosities. In order to prevent bubbling during the low temperature heat treatment, the thickness has to be controlled less than around 0.25 lm. From the
0.4 0.35
Thickness (µm)
order to obtain high Ic , processing for thicker YBCO films was investigated using the multicoating method [1]. On the other hand, we investigated the influence of the gas flow direction in the high temperature YBCO crystallization heat treatment, consequently the perpendicular gas flow to the tape length was effective to fabricate the uniform films [2]. Furthermore, in order to shorten the heat treatment time in the low temperature for making amorphous precursors, we developed a new precursor solution which reduces the generation of HF gas. In this paper, using this new TFA precursor, we fabricated a long Y123 tape conductor by the equipment with a reel-to-reel system, which has been newly developed. Superconducting properties and its distribution in the YBCO tape fabricated by this method on CeO2 /IBAD-Gd2 Zr2 O7 /Hastelloy is investigated.
917
0.3 0.25 0.2 0.15 0.1
Type A (61cp) Type B (54cp)
0.05 0
0
10
20
30
40
50
Traveling rate(mm/min)
Fig. 1. The traveling rate dependence of the thickness of the coated film for two solutions with different viscosities.
918
H. Fuji et al. / Physica C 412–414 (2004) 916–919
above investigation, it was found that the thicker film controllability could be expected in the solution with the viscosity of 54 cp because the slope is lower in Fig. 1. Then, the traveling rate of 30 mm/ min using the solution with the viscosity of 54 cp was selected for the coating in this study. On the other hand, the higher heating rate was used in the low temperature heat treatment for the new TFA solution [3]. Then, the temperature gradient of 104 °C/m was set in the furnace, where the heating rate should be 3.1 °C/min in the case of 30 mm/min of the traveling rate. The continuous coating and low temperature heat treatment were carried out using the above conditions. Then the uniform precursor films on CeO2 /GZO-IBAD/Hastelloy were successfully obtained. Fig. 2 shows the surface morphology of the precursor tape and the smooth surface can be recognized. In order to realize a high performance tape, several factors should be simultaneously optimized, such as the heat treatment temperature, the heat treatment time, P(H2 O), the gas flow direction, etc. In the factors, it was already found that the transverse gas flow to the tape length is necessary to obtain the uniform reaction. Then, we developed the reel-to-reel equipment with the transverse gas flow system for the long tape fabrication. In this equipment, the heat treatment time is controlled by combination of the reacted zone length, in which the humid gas is flowed in the transverse direction, the growth conditions including P(H2 O), temperature, gas flow rates, etc., which determines the growth rate, and the
traveling rate. In this study, the heat treatment time was changed by the reacted zone length. In the case of the short reacted zone, existence of unreacted BaF2 crystals phase was recognized in the heat-treated film due to the short reaction time. On the other hand, in the case of the long react zone, the tape has a white and rough surface as shown in Fig. 3(a). Both tapes revealed lower Ic values than 100 A at 77 K. Finally, the heat treatment time was optimized and a black and shiny 0.25 m long tape was obtained. The tape consisted of textured Y123 phase crystals without un-reacted phase crystals such as BaF2 as shown in Fig. 3(b), and reveal high Ic value of 210 A as shown in Fig. 4.
Fig. 3. The FIB SIM images of YBCO films.
300
Over 240A
250
210A
Ic (A)
200 150 100 50 0 5
10
20
25
End to End
Position (cm)
Fig. 2. The surface morphology of the precursor tape.
Fig. 4. Superconducting properties and its distribution in the YBCO tape fabricated by this method on CeO2 /IBADGd2 Zr2 O7 /Hastelloy.
H. Fuji et al. / Physica C 412–414 (2004) 916–919
919
4. Conclusion
Acknowledgements
The uniform precursor film was fabricated using the advanced TFA solution after investigation of the optimized coating conditions. A large scale equipment for continuous long tape production was developed based on the knowledge of the influence of the gas flow direction. Additionally, the optimum condition for the high temperature crystallization heat treatment has been investigated by changing the reaction time. Consequently, a quality e 0.25 m long tape was successfully fabricated by the continuous reel-to-reel systems. Ic property and its distribution of the YBCO tape fabricated by this method on CeO2 /IBAD-Gd2 Zr2 O7 /Hastelloy were evaluated. The high Ic value of 210 A from the end to end measurement at 77.3 K in self-fields was attained.
This work is supported by the new Energy and Industrial Technology Development Organization (NEDO) as Collaborative Research and Development of Fundamental Technologies for Superconductivity Applications.
References [1] H. Fuji, T. Honjo, Y. Nakamura, T. Izumi, Y. Shiohara, R. Teranishi, M. Yoshimura, Y. Iijima, T. Saitoh, Physica C 378–381 (Part 2) (2002) 1013. [2] H. Fuji, T. Honjo, R. Teranishi, Y. Tokunaga, J. Shibata, T. Izumi, Y. Shiohara, Y. Iijima, T. Saitoh, Physica C 392–396 (2003) 905. [3] Y. Tokunaga, H. Fuji, R. Teranishi, J. Matsuda, S. Asada, T. Honjo T. Izumi, Y. Shiohara, Y. Iijima, T. Saitoh, T.Goto, A. Yajima., Proceedings of EUCAS 2003, in press.
Processing for long YBCO coated conductors by advanced TFA-MOD process Hiroshi Fuji a,*, Tetsuji Honjo a, Ryo Teranishi a, Yoshitaka Tokunaga a, Junko Matsuda a, Shigenobu Asada a, Yutaka Yamada a, Teruo Izumi a, Yuh Shiohara a, Yasuhiro Iijima b, Takashi Saitoh b, Atsushi Kaneko c, Kiyoshi Murata c a
Superconductivity Research Laboratory, ISTEC, Shinonome 1-10-13, Koto-ku, Tokyo 135-0062, Japan b Fujikura Ltd., 1-5-1, Kiba, Koto-ku, Tokyo 135-8512, Japan c Shibaura Institute of Technology, 3-9-14, Shibaura, Minato-ku, Tokyo 108-8548, Japan Received 29 October 2003; accepted 2 February 2004 Available online 1 June 2004
Abstract The long tape process was developed using the advanced TFA precursor solution. In a long tape production, the advanced TFA precursor solution was coated by a die-coater using the reel-to-reel system, and the multi-coating method was applied for thicker film fabrication. We successfully fabricated long uniform precursor films. In the high temperature treatment, a large scale equipment for the continuous long tape process was developed. This equipment had a perpendicular gas flow system to the tape length which is effective to fabricate the uniform films. Ic values and its distribution in the YBCO tape fabricated by this method on CeO2 /IBAD-Gd2 Zr2 O7 /Hastelloy were measured. And the uniform and high performance was confirmed. A 0.25 m long YBCO film with 1.38 lm in thickness on the metal substrate shows the high Ic performance of 210 A with end to end at 77.3 K in self-fields. Ó 2004 Published by Elsevier B.V. PACS: 81.15.)z; 74.72.Bk; 81.10.Jt Keywords: TFA-MOD process; IBAD
1. Introduction The MOD process for YBa2 Cu3 O7x (Y123) using metal trifluoroacetate (TFA) precursors is
*
Corresponding author. Tel.: +81-3-3536-5711; fax: +81-33536-5705. E-mail address: [email protected] (H. Fuji). 0921-4534/$ - see front matter Ó 2004 Published by Elsevier B.V. doi:10.1016/j.physc.2004.02.206
considered to be a strong candidate as a low cost process for coated conductors, since the TFAMOD process is essentially a non vacuum process. Additionally, it has been well confirmed that this process has an advantage to provide a high Jc film of MA/cm2 class. In our previous work, it was confirmed that the combination of CeO2 by PLD on Gd2 Zr2 O7 by IBAD is effective buffer layers on a metal substrate for the TFA-MOD process. In
H. Fuji et al. / Physica C 412–414 (2004) 916–919
2. Experimental A CeO2 buffer layer was deposited on IBADGd2 Zr2 O7 /Hastelloy substrates by pulse laser deposition (PLD) method at 600 °C in about 30 mTorr O2 gas atmosphere. The deposition was carried out by the reel-to-reel system and the thickness of the CeO2 layer was controlled to be about 1.0 lm thick. In the case of the longer tape, a new TFA precursor solution [3] was coated on substrates by a die-coater using the continuous reel-to-reel system. In order to control the thickness of coated films, the traveling rate dependence of the thickness using the solutions with different viscosities were investigated. The traveling rate was changed from 10 to 40 mm/min for the solutions with the viscosities of 54 and 61 cp. The viscosity of the solution was controlled by the ratio of the salts and the solvent. The heat treatment was conducted by two stages at which are the low temperature and at the successive high temperature. In the low temperature heat treatment, the coated films were decomposed to the mixture consisted of amorphous, oxides, fluorides and oxyfluoride, etc. which is called as a precursor film using the heating rate of 5 °C/min to 400 °C in a moist O2 atmosphere. The processes of the coating
and the low temperature heat treatment were repeated several times to obtain thick precursor films. In the high temperature heat treatment, the films were traveled in a long tube furnace held at 760 °C in a forming gas of Ar and 0.1% O2 and 6.3% H2 O by the reel-to-reel system. Then, the forming gas was flowed along the perpendicular direction to the long tape. The crystallinity of the long Y123 tape was evaluated by XRD measurements and FIB SIM images. Ic performance and its distribution of these Y123 films were measured by a four-probe transport method.
3. Results and discussion Fig. 1 shows the traveling rate dependence of the thickness of the coated film for two solutions with different viscosities. Both curves revealed a liner relationship. This phenomenon is in a good agreement with the prediction by the following equation: T ¼ kðV gÞn
ð1Þ
(T : thickness; k: constant; V : traveling rate; g: viscosity of the solutions; n ¼ 1 at this study). In this study, the viscosity values of the solutions were controlled to be about 54 and 61 cp. The difference in the slopes in Fig. 1 is consistent with the difference from that in the viscosities. In order to prevent bubbling during the low temperature heat treatment, the thickness has to be controlled less than around 0.25 lm. From the
0.4 0.35
Thickness (µm)
order to obtain high Ic , processing for thicker YBCO films was investigated using the multicoating method [1]. On the other hand, we investigated the influence of the gas flow direction in the high temperature YBCO crystallization heat treatment, consequently the perpendicular gas flow to the tape length was effective to fabricate the uniform films [2]. Furthermore, in order to shorten the heat treatment time in the low temperature for making amorphous precursors, we developed a new precursor solution which reduces the generation of HF gas. In this paper, using this new TFA precursor, we fabricated a long Y123 tape conductor by the equipment with a reel-to-reel system, which has been newly developed. Superconducting properties and its distribution in the YBCO tape fabricated by this method on CeO2 /IBAD-Gd2 Zr2 O7 /Hastelloy is investigated.
917
0.3 0.25 0.2 0.15 0.1
Type A (61cp) Type B (54cp)
0.05 0
0
10
20
30
40
50
Traveling rate(mm/min)
Fig. 1. The traveling rate dependence of the thickness of the coated film for two solutions with different viscosities.
918
H. Fuji et al. / Physica C 412–414 (2004) 916–919
above investigation, it was found that the thicker film controllability could be expected in the solution with the viscosity of 54 cp because the slope is lower in Fig. 1. Then, the traveling rate of 30 mm/ min using the solution with the viscosity of 54 cp was selected for the coating in this study. On the other hand, the higher heating rate was used in the low temperature heat treatment for the new TFA solution [3]. Then, the temperature gradient of 104 °C/m was set in the furnace, where the heating rate should be 3.1 °C/min in the case of 30 mm/min of the traveling rate. The continuous coating and low temperature heat treatment were carried out using the above conditions. Then the uniform precursor films on CeO2 /GZO-IBAD/Hastelloy were successfully obtained. Fig. 2 shows the surface morphology of the precursor tape and the smooth surface can be recognized. In order to realize a high performance tape, several factors should be simultaneously optimized, such as the heat treatment temperature, the heat treatment time, P(H2 O), the gas flow direction, etc. In the factors, it was already found that the transverse gas flow to the tape length is necessary to obtain the uniform reaction. Then, we developed the reel-to-reel equipment with the transverse gas flow system for the long tape fabrication. In this equipment, the heat treatment time is controlled by combination of the reacted zone length, in which the humid gas is flowed in the transverse direction, the growth conditions including P(H2 O), temperature, gas flow rates, etc., which determines the growth rate, and the
traveling rate. In this study, the heat treatment time was changed by the reacted zone length. In the case of the short reacted zone, existence of unreacted BaF2 crystals phase was recognized in the heat-treated film due to the short reaction time. On the other hand, in the case of the long react zone, the tape has a white and rough surface as shown in Fig. 3(a). Both tapes revealed lower Ic values than 100 A at 77 K. Finally, the heat treatment time was optimized and a black and shiny 0.25 m long tape was obtained. The tape consisted of textured Y123 phase crystals without un-reacted phase crystals such as BaF2 as shown in Fig. 3(b), and reveal high Ic value of 210 A as shown in Fig. 4.
Fig. 3. The FIB SIM images of YBCO films.
300
Over 240A
250
210A
Ic (A)
200 150 100 50 0 5
10
20
25
End to End
Position (cm)
Fig. 2. The surface morphology of the precursor tape.
Fig. 4. Superconducting properties and its distribution in the YBCO tape fabricated by this method on CeO2 /IBADGd2 Zr2 O7 /Hastelloy.
H. Fuji et al. / Physica C 412–414 (2004) 916–919
919
4. Conclusion
Acknowledgements
The uniform precursor film was fabricated using the advanced TFA solution after investigation of the optimized coating conditions. A large scale equipment for continuous long tape production was developed based on the knowledge of the influence of the gas flow direction. Additionally, the optimum condition for the high temperature crystallization heat treatment has been investigated by changing the reaction time. Consequently, a quality e 0.25 m long tape was successfully fabricated by the continuous reel-to-reel systems. Ic property and its distribution of the YBCO tape fabricated by this method on CeO2 /IBAD-Gd2 Zr2 O7 /Hastelloy were evaluated. The high Ic value of 210 A from the end to end measurement at 77.3 K in self-fields was attained.
This work is supported by the new Energy and Industrial Technology Development Organization (NEDO) as Collaborative Research and Development of Fundamental Technologies for Superconductivity Applications.
References [1] H. Fuji, T. Honjo, Y. Nakamura, T. Izumi, Y. Shiohara, R. Teranishi, M. Yoshimura, Y. Iijima, T. Saitoh, Physica C 378–381 (Part 2) (2002) 1013. [2] H. Fuji, T. Honjo, R. Teranishi, Y. Tokunaga, J. Shibata, T. Izumi, Y. Shiohara, Y. Iijima, T. Saitoh, Physica C 392–396 (2003) 905. [3] Y. Tokunaga, H. Fuji, R. Teranishi, J. Matsuda, S. Asada, T. Honjo T. Izumi, Y. Shiohara, Y. Iijima, T. Saitoh, T.Goto, A. Yajima., Proceedings of EUCAS 2003, in press.