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Long lengths of Bi(2223) superconducting tapes
Cryogenics 37 (1997) S-599 0 1997 Published by Elsevier Science Ltd Printed in Great Britain. All rights reserved
PII: SOOll-2275(97)00055-6
OOII-2275/97/$17.00
Long lengths of Bi(2223) superconducting tapes G. Grasso, F. Marti, Y. Huang and R. Fliikiger Depar-tement de Physique de la Matiere Condensee and Groupe de Physique Appliquee, 24 quai Ernest-Ansermet, CH-1211 Geneve 4, Switzerland
The optimization of the fabrication of mono- and multifilamentary Bi(2223) tapes has been carried out in order to improve their transport properties on long lengths. At present, critical current densities as high as 34.5 and 28 kA cm-* have been reproducibly achieved at the liquid nitrogen temperature on long mono- and multifilamentary tapes, respectively. The behaviour in magnetic field of the transport properties of these tapes has been studied. At 77 K, a field of 1 T applied along the &planes of the Bi(2223) grains reduces the critical current by a factor of five and three in mono- and multifilamentary samples, respectively. It has been found that the excellent behaviour of the transport properties of multifilamentary tapes in applied field is a direct consequence of the higher degree of texture of the Bi(2223) grains. 0 1997 Published by Elsevier Science Ltd. Keywords:
applications
of high I, superconductors;
The fabrication of long lengths of silver sheathed Bi(2223) tapes suitable for industrial applications requires a careful optimization of all the steps of the preparation process ‘. At present, critical current densities well above 20 kA cmm2 have been achieved at the liquid nitrogen temperature on long mono- and multifilamentary tapes 2m4.However, these values are still considerably lower than those obtained on short, pressed tapes, which have reached critical current densities ranging between 66 and 69 kA cmm2 at 77 K 5,6. Moreover, local j, measurements have shown that the Bi(2223) grains can carry critical currents in excess of 100 kA cm-* 7m9. Nearly all the possible industrial applications of Bi(2223) tapes involve high magnetic fields. In magnetic field, the critical current at 77 K reduces generally by a factor of three to six compared to the zero field value if a field of 1 T is applied perpendicular to the tape normal. However, the critical current reduces much faster if the field is applied along the tape normal, the current-voltage characteristics showing pure ohmic behaviour above 0.5 T at the liquid nitrogen temperature. The well-known reason for this low value of the irreversibility field is the lack of pinning of the flux lines when they are oriented along the c-axis; it has already been demonstrated that in irradiated tapes the columnar defects can shift the irreversibility line to very high fields ‘“,I I. However, in view of industrial applications it is necessary to find other ways to reduce the anisotropy of the transport critical current. In this work we describe the technique we have employed for fabricating monofilamentary tapes with j, value of 34.5 kA cmm2 over 0.5 m, and multifilamentary
Bi (22231
tapes with j, value of 28 kA cme2 over 14.5 m. The magnetic field dependence of the transport properties has been studied both at 77 and 4.2 K, and for different orientations of the tape.
Experimental Silver sheathed Bi(2223) tapes have been prepared by the powder-in-tube method. A calcined powder with nominal cation ratio Bi:Pb:Sr:Ca:Cu 1.72:0.34:1.83:1.97:3.13, and mainly composed of Bi, Pb(2212), Ca,PbO,, and CuO, is filled inside silver tubes with an initial density of about 65%-70%. The tubes are then swaged and drawn, down to a final diameter of about 1 to 2 mm. In the case of monofilamentary tapes, these wires are directly rolled in steps of about 10% thickness reduction down to a final thickness of about 100 pm. In the case of multifilamentary tapes, the wires are drawn in a hexagonal shape, and stacked inside another silver tube, which is deformed again by swaging, drawing, and rolling down to a final thickness of about 200-250 pm. A deformation speed of 1.5 cm ss’ has been employed for all the deformation processes. The tapes are then heat treated in order to form the Bi(2223) phase in a single piece of up to 15 m length. After the lirst heat treatment of about 40 h at a temperature of 837°C in air, the tape thickness has been reduced again by about 15% by rolling. The final heat treatment of up to 200 h is needed to reach the highest critical current density. Further details of the technique used are reported elsewhere I. Transport properties of these tapes have been measured both at 4.2
Cryogenics
1997 Volume
37, Number
10
597
Long length
Figure 1
Bi(2223)
SC tapes: G. Grass0 et al.
Typical transversal
cross-section
of a multifilamentary
and 77 K by directly immersing the tapes inside liquid nitrogen and liquid helium, respectively, and by soldering both current and voltage leads to the samples. A magnetic field up to 15 T has been applied both parallel and perpendicular to the tape surface. The critical current density has been measured with the standard four-probe method, and a criterion of 1 PV cm-’ has been chosen for the determination of j,.
Results Monofilamentary Ag sheathed Bi(2223) tapes prepared as described in the previous paragraph have reached a critical current density of 34.5 kA cmd2 over a length of 0.5 m at 77 K. The superconducting cross-section of these tapes is about 7.5 x 10e4 cm2, and the critical current is 26 A. Overall dimensions of these tapes are 80 pm in thickness, and 2.8 mm in width. Long multifilamentary tapes have been prepared with 37 and 55 filaments. At present, a critical current density of 28 kA cm-’ has been reproducibly achieved on 14.5 m long 37-filament tapes, which is the highest value published so far. The thickness of these tapes is about 200 pm and the width is about 3.5 mm. The superconducting cross-section represents about 20% of the overall section, and the critical current is about 40 A. A typical cross-section of a reacted 55-filament tape is shown in Figure 1. No crossing between adjacent filaments has been observed. Transport properties of short pieces of both mono- and multifilamentary tapes have been measured. In Figure 2 the measurements performed at 77 K are presented. In spite of the higher self-field critical current density, the monofilamentary tape presents a clearly faster drop of j, when a field is applied along the ah-planes of the Bi(2223) grains.
10
Field [T] Figure 2 Normalized critical current density of both mono- and multifilamentary tapes as a function of the applied field and of the tape orientation at 77 K
598
Cryogenics
1997 Volume
37, Number
10
tape with 55 filaments
Typically, for the monofilamentary tapes we have measured a j, value of about 6-7 kA cme2 at 1 T, which is about five times lower than the self-field value. At the same field, the multifilamentary tape still carries a critical current density of about 10 kA cme2, that is, only about a factor of three less than the self-field value. The differences between the transport properties of mono- and multifilamentary tapes are less marked if the field is applied along the tape normal, that is, the c-axis of the Bi(2223) grains. The critical current drops much faster than in the previous configuration, the critical current being negligibly small above 0.5 T. In the framework of the railway switch model 12, the differences between the transport properties of mono- and multifilamentary tapes can easily be explained by a different texture of the Bi( 2223) grains. In fact, according to this model, the field dependence measured with the field along the c-axis is mainly ‘pinning dependent’, which cannot be too different in mono- and multifilamentary tapes. On the contrary, the field dependence measured with the field oriented along &planes is also ‘microstructure dependent’, and is therefore more sensible to a variation in texture. From anisotropy measurements of the critical current density in constant magnetic field, it is possible to extract more information about the average texture of the Bi(2223) grains which contribute to the current transport. The complete anisotropy measurements are shown in Figure 3 for a fixed amplitude of the field of 0.15 T. In Figure 3 the normalized j, has been plotted as a function B cos( 0), where 8 is the angle between the field and the tape normal, in logarithmic scale. According to Ref. r3, we have determined an average misalignment angle of the Bi(2223) grains 8* of about 7” and 5” for the mono- and multifilamentary tapes, respectively. The same samples have been measured at 4.2 K, up to a field of 14 T applied along the &planes. The measurements are shown in Figure 4 for both increasing and decreasing magnetic field. The critical current shows a marked history dependence: at a fixed field, j, is generally much higher if the field has been decreased before the measurement from a higher value. This behaviour is quite common in bulk YBCO samples 14, and it is mainly imputable to some residual weak link like grain boundaries which are contributing to the current transport at low temperatures. At 4.2 K the self-field value of the critical current density of both mono- and multifilamentary samples is of the order of 200-220 kA cmm2. In a field of 15 T, the critical current reduces to about 70-80 kA cm-‘, for both mono- and multifilamentary tapes. This means that the better field dependence for the multifilamentary tapes observed at 77 K is no longer kept at lower temperatures.
Long length Bif2223)
[B cW~‘)lmono
0.4 -
SC tapes: G. Grass0 et al.
37 and 55 filaments in lengths up to 14.5 m. Critical current densities of 28 kA cm-* have been reproducibly achieved on 14.5 m, which is, at present, the highest published value. The measurements of the field dependence of the critical current density for different orientations of the tape have revealed that the multifilamentary samples show a higher degree of texture of the Bi(2223) grains than the monofilamentary ones, their effective misalignment angle being 7” and 5” in mono- and multifilamentary tapes, respectively. At 4.2 K, both mono- and multifilamentary tapes have reached a critical current density of about 200 kA cme2 in self-field. In spite of the difference observed at 77 K, the field dependencies of j, for mono- and multifilamentary tapes at 4.2 K show similar features, the critical current density measured at 15 T being about 70-80 kA cm-? for both samples. The high value of the engineering critical current density (well above 10 kA cm-* at 4.2 K for all the measuring field and for both mono- and multifilamentary tapes) is very promising in view of high field applications, the mechanical reinforcement being the biggest problem we still have to solve.
B cos(e) Figure 3 Angular dependence of the critical current density for both mono- and multifilamentary tapes at 77 K, for a field amplitude of 0.15 T. 0 is the angle between the field orientation and the tape normal
References 1. 2.
2.0rlO~
3. 4.
c
1.6x105
9 0 '-
5. 1.2x105
6. 8.0x104
7.
0
2
4
6
8
10
12
14
8.
6 (T&a)
9. Figure 4 Critical current density as a function of the field and of its history at 4.2 K for both mono- and multifilamentary tapes
Conclusions
10. 11. 12.
By the powder-in-tube method, long lengths of Bi(2223) have been successfully prepared. Critical current densities as high as 34.5 kA cm-’ have been achieved on 0.5 m long monofilamentary tapes at the liquid nitrogen temperature. Multifilamentary Bi(2223) tapes have been prepared with
13. 14.
Grasso, Cl., Jeremie, A. and Fltikiger, R., Supercond. Sci. Technol., 1995, 8, 827. Flttkiger, R., Grasso, G., Grivel, J. C., Hensel, B., Marti, F., Huang, Y. and Perin, A., Presented at the IWCC Conference, 24-27 May 1996, Kitakyushu, Japan. Riley, G. N., MRS 1996 Spring Meeting, 8-12 April 1996, San Francisco, CA. Sato, K., Ohkura, K., Hayashi, K., Hikata, T., Kaneko, T., Kato, T., Ueyama, M. and Fujikami, J., Proc. 7th US-Japan Workshop on High T, Superconductors, Tsukuba, Japan, 24-25 October 1995, p. 15. Yamada, Y., Satou, M., Murase, S., Kitamura, T. and Kamisada, Y. In Proc. 5rh 1% ‘92, eds. Y. Bando and Y. Yamauchi. Springer, Tokyo, 1993, p. 717. Li, Q., Brodersen, K., Hyuler, H. A. and Freltoft, T., Physica C, 1995, 217, 360. Grasso, G., Jeremie, A., Hensel, B. and Fltlkiger, R., Physica C, 1995, 241, 45. Larbalestier, D. C., Cai, X. Y., Feng, Y., Edelmann, H., Umezawa, A., Riley, G. N. and Carter, W. L., Physica C, 1994, 221, 299. Lelovic, M., Krishnaraj, P., Eror, N. G., Iyer, A. N. and Balachandran, U., Supercond. Sci. Technol., 1996, 9, 201. Safar, H., Cho, J. H., Fleshler, S., Maley, M. P., Willis, J. 0. and Krushin-Elbaum, L., Appl. Phys. Left., 1995, 67, 130. Hensel, B., Victoria, M., Grindatto, D. and Fltlkiger, R., in preparation. Hensel, B., Grasso, G. and Fliikiger, R., Phys. Rev. B, 1995, 51, 15456. Hensel, B., Grivel, J.-C., Jeremie, A., Perin, A., Pollini, A. and Flukiger, R., Physica C. 1993, 216, 339. D’yachenko, A. I., Hysteresis of transport critical current of high T, superconductors in strong magnetic fields. Theory. Physica C, 1994, 213, 167.
Cryogenics
1997 Volume
37, Number
IO
599
PII: SOOll-2275(97)00055-6
OOII-2275/97/$17.00
Long lengths of Bi(2223) superconducting tapes G. Grasso, F. Marti, Y. Huang and R. Fliikiger Depar-tement de Physique de la Matiere Condensee and Groupe de Physique Appliquee, 24 quai Ernest-Ansermet, CH-1211 Geneve 4, Switzerland
The optimization of the fabrication of mono- and multifilamentary Bi(2223) tapes has been carried out in order to improve their transport properties on long lengths. At present, critical current densities as high as 34.5 and 28 kA cm-* have been reproducibly achieved at the liquid nitrogen temperature on long mono- and multifilamentary tapes, respectively. The behaviour in magnetic field of the transport properties of these tapes has been studied. At 77 K, a field of 1 T applied along the &planes of the Bi(2223) grains reduces the critical current by a factor of five and three in mono- and multifilamentary samples, respectively. It has been found that the excellent behaviour of the transport properties of multifilamentary tapes in applied field is a direct consequence of the higher degree of texture of the Bi(2223) grains. 0 1997 Published by Elsevier Science Ltd. Keywords:
applications
of high I, superconductors;
The fabrication of long lengths of silver sheathed Bi(2223) tapes suitable for industrial applications requires a careful optimization of all the steps of the preparation process ‘. At present, critical current densities well above 20 kA cmm2 have been achieved at the liquid nitrogen temperature on long mono- and multifilamentary tapes 2m4.However, these values are still considerably lower than those obtained on short, pressed tapes, which have reached critical current densities ranging between 66 and 69 kA cmm2 at 77 K 5,6. Moreover, local j, measurements have shown that the Bi(2223) grains can carry critical currents in excess of 100 kA cm-* 7m9. Nearly all the possible industrial applications of Bi(2223) tapes involve high magnetic fields. In magnetic field, the critical current at 77 K reduces generally by a factor of three to six compared to the zero field value if a field of 1 T is applied perpendicular to the tape normal. However, the critical current reduces much faster if the field is applied along the tape normal, the current-voltage characteristics showing pure ohmic behaviour above 0.5 T at the liquid nitrogen temperature. The well-known reason for this low value of the irreversibility field is the lack of pinning of the flux lines when they are oriented along the c-axis; it has already been demonstrated that in irradiated tapes the columnar defects can shift the irreversibility line to very high fields ‘“,I I. However, in view of industrial applications it is necessary to find other ways to reduce the anisotropy of the transport critical current. In this work we describe the technique we have employed for fabricating monofilamentary tapes with j, value of 34.5 kA cmm2 over 0.5 m, and multifilamentary
Bi (22231
tapes with j, value of 28 kA cme2 over 14.5 m. The magnetic field dependence of the transport properties has been studied both at 77 and 4.2 K, and for different orientations of the tape.
Experimental Silver sheathed Bi(2223) tapes have been prepared by the powder-in-tube method. A calcined powder with nominal cation ratio Bi:Pb:Sr:Ca:Cu 1.72:0.34:1.83:1.97:3.13, and mainly composed of Bi, Pb(2212), Ca,PbO,, and CuO, is filled inside silver tubes with an initial density of about 65%-70%. The tubes are then swaged and drawn, down to a final diameter of about 1 to 2 mm. In the case of monofilamentary tapes, these wires are directly rolled in steps of about 10% thickness reduction down to a final thickness of about 100 pm. In the case of multifilamentary tapes, the wires are drawn in a hexagonal shape, and stacked inside another silver tube, which is deformed again by swaging, drawing, and rolling down to a final thickness of about 200-250 pm. A deformation speed of 1.5 cm ss’ has been employed for all the deformation processes. The tapes are then heat treated in order to form the Bi(2223) phase in a single piece of up to 15 m length. After the lirst heat treatment of about 40 h at a temperature of 837°C in air, the tape thickness has been reduced again by about 15% by rolling. The final heat treatment of up to 200 h is needed to reach the highest critical current density. Further details of the technique used are reported elsewhere I. Transport properties of these tapes have been measured both at 4.2
Cryogenics
1997 Volume
37, Number
10
597
Long length
Figure 1
Bi(2223)
SC tapes: G. Grass0 et al.
Typical transversal
cross-section
of a multifilamentary
and 77 K by directly immersing the tapes inside liquid nitrogen and liquid helium, respectively, and by soldering both current and voltage leads to the samples. A magnetic field up to 15 T has been applied both parallel and perpendicular to the tape surface. The critical current density has been measured with the standard four-probe method, and a criterion of 1 PV cm-’ has been chosen for the determination of j,.
Results Monofilamentary Ag sheathed Bi(2223) tapes prepared as described in the previous paragraph have reached a critical current density of 34.5 kA cmd2 over a length of 0.5 m at 77 K. The superconducting cross-section of these tapes is about 7.5 x 10e4 cm2, and the critical current is 26 A. Overall dimensions of these tapes are 80 pm in thickness, and 2.8 mm in width. Long multifilamentary tapes have been prepared with 37 and 55 filaments. At present, a critical current density of 28 kA cm-’ has been reproducibly achieved on 14.5 m long 37-filament tapes, which is the highest value published so far. The thickness of these tapes is about 200 pm and the width is about 3.5 mm. The superconducting cross-section represents about 20% of the overall section, and the critical current is about 40 A. A typical cross-section of a reacted 55-filament tape is shown in Figure 1. No crossing between adjacent filaments has been observed. Transport properties of short pieces of both mono- and multifilamentary tapes have been measured. In Figure 2 the measurements performed at 77 K are presented. In spite of the higher self-field critical current density, the monofilamentary tape presents a clearly faster drop of j, when a field is applied along the ah-planes of the Bi(2223) grains.
10
Field [T] Figure 2 Normalized critical current density of both mono- and multifilamentary tapes as a function of the applied field and of the tape orientation at 77 K
598
Cryogenics
1997 Volume
37, Number
10
tape with 55 filaments
Typically, for the monofilamentary tapes we have measured a j, value of about 6-7 kA cme2 at 1 T, which is about five times lower than the self-field value. At the same field, the multifilamentary tape still carries a critical current density of about 10 kA cme2, that is, only about a factor of three less than the self-field value. The differences between the transport properties of mono- and multifilamentary tapes are less marked if the field is applied along the tape normal, that is, the c-axis of the Bi(2223) grains. The critical current drops much faster than in the previous configuration, the critical current being negligibly small above 0.5 T. In the framework of the railway switch model 12, the differences between the transport properties of mono- and multifilamentary tapes can easily be explained by a different texture of the Bi( 2223) grains. In fact, according to this model, the field dependence measured with the field along the c-axis is mainly ‘pinning dependent’, which cannot be too different in mono- and multifilamentary tapes. On the contrary, the field dependence measured with the field oriented along &planes is also ‘microstructure dependent’, and is therefore more sensible to a variation in texture. From anisotropy measurements of the critical current density in constant magnetic field, it is possible to extract more information about the average texture of the Bi(2223) grains which contribute to the current transport. The complete anisotropy measurements are shown in Figure 3 for a fixed amplitude of the field of 0.15 T. In Figure 3 the normalized j, has been plotted as a function B cos( 0), where 8 is the angle between the field and the tape normal, in logarithmic scale. According to Ref. r3, we have determined an average misalignment angle of the Bi(2223) grains 8* of about 7” and 5” for the mono- and multifilamentary tapes, respectively. The same samples have been measured at 4.2 K, up to a field of 14 T applied along the &planes. The measurements are shown in Figure 4 for both increasing and decreasing magnetic field. The critical current shows a marked history dependence: at a fixed field, j, is generally much higher if the field has been decreased before the measurement from a higher value. This behaviour is quite common in bulk YBCO samples 14, and it is mainly imputable to some residual weak link like grain boundaries which are contributing to the current transport at low temperatures. At 4.2 K the self-field value of the critical current density of both mono- and multifilamentary samples is of the order of 200-220 kA cmm2. In a field of 15 T, the critical current reduces to about 70-80 kA cm-‘, for both mono- and multifilamentary tapes. This means that the better field dependence for the multifilamentary tapes observed at 77 K is no longer kept at lower temperatures.
Long length Bif2223)
[B cW~‘)lmono
0.4 -
SC tapes: G. Grass0 et al.
37 and 55 filaments in lengths up to 14.5 m. Critical current densities of 28 kA cm-* have been reproducibly achieved on 14.5 m, which is, at present, the highest published value. The measurements of the field dependence of the critical current density for different orientations of the tape have revealed that the multifilamentary samples show a higher degree of texture of the Bi(2223) grains than the monofilamentary ones, their effective misalignment angle being 7” and 5” in mono- and multifilamentary tapes, respectively. At 4.2 K, both mono- and multifilamentary tapes have reached a critical current density of about 200 kA cme2 in self-field. In spite of the difference observed at 77 K, the field dependencies of j, for mono- and multifilamentary tapes at 4.2 K show similar features, the critical current density measured at 15 T being about 70-80 kA cm-? for both samples. The high value of the engineering critical current density (well above 10 kA cm-* at 4.2 K for all the measuring field and for both mono- and multifilamentary tapes) is very promising in view of high field applications, the mechanical reinforcement being the biggest problem we still have to solve.
B cos(e) Figure 3 Angular dependence of the critical current density for both mono- and multifilamentary tapes at 77 K, for a field amplitude of 0.15 T. 0 is the angle between the field orientation and the tape normal
References 1. 2.
2.0rlO~
3. 4.
c
1.6x105
9 0 '-
5. 1.2x105
6. 8.0x104
7.
0
2
4
6
8
10
12
14
8.
6 (T&a)
9. Figure 4 Critical current density as a function of the field and of its history at 4.2 K for both mono- and multifilamentary tapes
Conclusions
10. 11. 12.
By the powder-in-tube method, long lengths of Bi(2223) have been successfully prepared. Critical current densities as high as 34.5 kA cm-’ have been achieved on 0.5 m long monofilamentary tapes at the liquid nitrogen temperature. Multifilamentary Bi(2223) tapes have been prepared with
13. 14.
Grasso, Cl., Jeremie, A. and Fltikiger, R., Supercond. Sci. Technol., 1995, 8, 827. Flttkiger, R., Grasso, G., Grivel, J. C., Hensel, B., Marti, F., Huang, Y. and Perin, A., Presented at the IWCC Conference, 24-27 May 1996, Kitakyushu, Japan. Riley, G. N., MRS 1996 Spring Meeting, 8-12 April 1996, San Francisco, CA. Sato, K., Ohkura, K., Hayashi, K., Hikata, T., Kaneko, T., Kato, T., Ueyama, M. and Fujikami, J., Proc. 7th US-Japan Workshop on High T, Superconductors, Tsukuba, Japan, 24-25 October 1995, p. 15. Yamada, Y., Satou, M., Murase, S., Kitamura, T. and Kamisada, Y. In Proc. 5rh 1% ‘92, eds. Y. Bando and Y. Yamauchi. Springer, Tokyo, 1993, p. 717. Li, Q., Brodersen, K., Hyuler, H. A. and Freltoft, T., Physica C, 1995, 217, 360. Grasso, G., Jeremie, A., Hensel, B. and Fltlkiger, R., Physica C, 1995, 241, 45. Larbalestier, D. C., Cai, X. Y., Feng, Y., Edelmann, H., Umezawa, A., Riley, G. N. and Carter, W. L., Physica C, 1994, 221, 299. Lelovic, M., Krishnaraj, P., Eror, N. G., Iyer, A. N. and Balachandran, U., Supercond. Sci. Technol., 1996, 9, 201. Safar, H., Cho, J. H., Fleshler, S., Maley, M. P., Willis, J. 0. and Krushin-Elbaum, L., Appl. Phys. Left., 1995, 67, 130. Hensel, B., Victoria, M., Grindatto, D. and Fltlkiger, R., in preparation. Hensel, B., Grasso, G. and Fliikiger, R., Phys. Rev. B, 1995, 51, 15456. Hensel, B., Grivel, J.-C., Jeremie, A., Perin, A., Pollini, A. and Flukiger, R., Physica C. 1993, 216, 339. D’yachenko, A. I., Hysteresis of transport critical current of high T, superconductors in strong magnetic fields. Theory. Physica C, 1994, 213, 167.
Cryogenics
1997 Volume
37, Number
IO
599