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Texturation of Bi-based 2212 superconducting bulk ceramics
,. . . . . . . .
CRYSTAL O R O W T H
ELSEVIER
Journal of Crystal Growth 166 (1996) 281-285
Texturation of Bi-based 2212 superconducting bulk ceramics S. Stassen
a,*,
A. Vanderschueren
b, R.
Cloots a,b, A. Rulmont
a, M.
Ausloos c,l
a SUPRAS, Chemistry Institute B6, University ofLibge, Sart-Tilman, B-4000 Libge, Belgium b SUPRAS, Montefiore Electricity Institute B28, University ofLibge, Sart-Tilman, B-4000 Libge, Belgium c SUPRAS, Physics Institute B5, University ofLibge, Sart-Tilman, B-4000 Libge, Belgium
Abstract
The magnetic texturing growth (Mag TG) technique has been applied for the first time to 2212 powder (BieSrzCao.sDyo.2Cu20 v) in order to obtain well-textured, Bi-based bulk ceramics. The sample has been analyzed by X-ray diffraction analysis, poiarized light microscopy, scanning electron microscopy, and EDX analysis. Electric resistivity measurements have also been made. A well-textured sample with an intergrowth of two phases was observed: the expected 2212 superconducting phase sandwiching a non-superconducting Bi-rich phase. The electric transition is quite sharp with a Tc around 87 K. Some further experiments in gold and copper tubes have been performed and offer the possibility of providing well-textured coils.
1. Introduction
The best way to obtain superconducting ceramics with good electrical properties such as high critical current density is to texture them. Magnetic texturing growth (Mag TG) is certainly one of the most competitive techniques to achieve such a goal. It has been applied extensively to the YBCO system, often doped by rare-earth ions [1-4]. However, the Mag TG has never been tried on Bi-based systems. In this paper we present for the first time magnetic textured 2212 bulk ceramics. The ceramic is found to be well-textured.
* Corresponding author. i E-mail: [email protected].
2. E x p e r i m e n t a l details
2.1. Textured bulk 2212 ceramics
The synthesis starts by mixing stoichiometric amounts of BieO 3, CaCO 3, SrCO 3, CuCO 3 • Cu(OH) 2 and DyeO 3. The mixture is then treated at 820°C for 48 h at a heating rate of 150°C/h including two intermediate grindings. The resulting crystalline powder Bi2Sr2Ca0.sDY0.zCueOy is then introduced into an alumina crucible and placed in a vertical furnace. A 1.2 T magnetic field is applied horizontally during the whole process. The sample is heated to 950°C at a heating rate of 150°C/h. It is then cooled down to 800°C at 2 ° C / h followed by a 5 0 ° C / h cooling rate to room temperature. The sample is then removed from the alumina crucible in which texturation took place. A zero field run has also been performed as a control procedure.
0022-0248/96/$15.00 Copyright © 1996 Elsevier Science B.V. All rights reserved PII S0022-0248(96)00129-7
282
S. Stassen et al./Journal ~f Co'stal Growth 166 (1996) 281-285
X-ray diffractograms have been recorded with a Siemens D5000 diffractometer usin~ Cu K o~ monochromatized radiation (A = 1.5406 A). Optically polarized light microscopy analysis has been performed on the sample. Optimal color contrast to make visible interesting structural details has been attempted. EDX analysis has been performed on a Cambridge scanning electron microscope (SEM) at the Cockerill Research Center in Liege. The electrical measurements were made with the four-probe technique in an automated set-up [5]. Data were taken from room temperature down to about 40 K.
3. Results and discussion 3.1. Textured bulk 2212 ceramics
Fig. 1 shows the X-ray diffraction patterns recorded for the cross-section perpendicular to the applied magnetic induction direction. The sample treated in the 1.2 T magnetic field is well textured since the (00/) reflection peaks are almost the only ones visible in the diffraction pattern (Fig. lb) and are very much enhanced when compared to the zero-field specimen (Fig. la). A splitting of the (00/) peaks is observed and can be explained by the intergrowth of the so-called N and D phases which we discussed in a previous paper [6]. Those two phases result from the partial substitution of Ca by Dy. They have slightly different c parameters depending on which sites Dy occupies [7]. X-ray diffraction analysis does not show any particular secondary phase.
2.2. Textured wire
The preparation of textured coils follows the same procedure, except for the container which is either a gold or a copper tube closed at one end.
6°1 960
1
(b)
>~ 640-
O
320-
30
4o
~'4
5b
Diffraction angle (°20) (L=1.5406A) Fig. 1. X-ray diffraction patterns of Bi2Sr2Ca0 sDyo 2Cu20,. sample textured in 1.2 T. The observation plane is perpendicular to the applied magnetic field.
S. Stassen et al. / Journal of Crystal Growth 166 (1996) 281-285
The polarized light microscopy pictures (Fig. 2) exhibit a typical textured microstructure. The picture in Fig. 2 (top) has been taken with the observed plane containing the c-axis whereas Fig. 2 (bottom) represents the same sample with ab-planes being the observation plane. The sample is thus well textured with a stacking of large platelets lying along the direction of the applied magnetic field. Magnetic texturing growth orients the sample with the c-axis parallel to the magnetic field direction since Dy is known to be a parallel aligner [8]. EDX analysis has been performed on the surface of the polished sample for the plane containing the c-axis (see Fig. 3) and for which the stacking of ab platelets is visible. EDX analysis confirms the presence of two types of phases. Moreover some copper oxide spots are also visible. The dark grey layers ( # 1, 3, 5, 7 in Fig. 3) are made of regular 2212 material (arrows in Fig. 2). The light grey layers ( #
283
Fig. 3. SEM pictures of Bi2SrzCao.sDyo.2Cu2Oy sample textured in 1.2 T. The c-axis lies in the observation plane.
2, 4, 6, 8 in Fig. 3) are made of phases rich in Bi, sometimes poor in Ca ( # 4 and 6 in Fig. 3), sometimes poor in Cu ( # 2 and 8 in Fig. 3) depending on the presence of copper oxide spots (black phase in Fig. 3) in that layer. Copper oxide crystallizes from the melt to form dendrites or spots during the cooling part of the process. They probably result from an excessive cooling rate. Their formation implies that the neighboring phase from which they arise is poor in copper. In further work, we will try to avoid their formation by lowering the cooling rate. Microscopic and EDX analysis thus reveal the intergrowth of two phases: the expected 2212 superconducting phase sandwiching a non-superconducting Bi-rich phase. Electrical resistivity versus temperature curves are show in Fig. 4 for the cases in which the currents are applied parallel ( I ) or perpendicular ( 0 ) to the magnetic induction direction. The anisotropy of the resistivity curves confirms the texture. The resistivity above T~ is much higher in the c-direction than in the ab-planes. This result is consistent with the fact that the superconducting currents flow in the copper oxide planes. The derivative curves (not shown) of the electrical resistivity exhibit a T~ of about 87 K characteristic of well-connected 2212 materials. 3.2. Textured wire
Fig. 2. Polarized light optical m i c r o s c o p y of Bi~Sr2Ca0.sDY0.zCuzQ sample textured in 1.2 T. (Top) The c-axis lies in the observation plane and is perpendicular to the layers. (Bottom) The observation plane is in the ab-planes.
First, we tried to replace the alumina crucible by a copper tube in order to get a textured superconducting wire. Unfortunately, the high reactivity of copper led to a multiphase system at the interface between the remainder of the tube and the 2212 core.
284
S. Stassen et al. / Journal of Crystal Growth 166 (1996) 281-285 1400
,
,
,
1500 1200 1100 1000 900 800
small transition since at room temperature the resistivity is already very low due to percolation through the Au tube. The resistivity versus temperature curve (Fig. 5) exhibits a typical 2212 " c l e a n " material transition comparable to that observed for the textured material in an alumina container.
7OO 6OO 500
4. Conclusion
400 3OO 2OO tO0 0
!
.
.
75
.
.
.
.
90
105
Temperature (K) Fig. 4. Electrical resistivity p versus temperature of Bi2Sr2Ca0.8Dy0.2Cu2Oy sample textured in 1.2 T for cases in which the current is applied parallel ( I ) or perpendicular (O) to the magnetic field direction.
We have thus decided to make a new attempt with a more inert material such as a gold tube. That experiment was successful and no interfacial secondary reaction took place. The superconducting 2212 material was then removed from the Au tube to be analyzed and measured. Resistivity measurement on the entire system after the Au wrapping had been removed gives only a
8
. . . .
i
. . . .
t
. . . .
i
. . . .
i
. . . .
v
This magnetic texturing growth technique offers an easy route to synthesize textured 2212 bulk ceramics with good anisotropic properties. The sample is made of two phases: the expected 2212 superconducting phase sandwiching a non-superconducting Bi-rich phase. The splitting of the (00l) reflection peaks is observed and is explained by the intergrowth of N and D phases with two different c parameters. An application of this technique offers the possibility of producing a well-textured wire.
Acknowledgements R.C. and S.S. are particularly grateful to the FNRS for a research grant. This work is part of the S U P R A N A T S U / 0 2 / 1 3 Superconductivity Impulse Program of the Services for Scientific, Technical and Cultural (SSTC) Affairs. An ARC (64-99/174) grant from the Ministry of Higher Education through the University of Liege Research Council is also acknowledged. The authors are grateful to Professor H.W. Vanderschueren for allowing them to use the MIEL laboratory and to Dr. M. Michellini at the Cockerill Research Center for the EDX facilities.
2
References 60
70
80
90
100
10
T e m p e r a t u r e (K) Fig. 5. Electrical resistivity p versus temperature of Bi2Sr2CaosDyo2Cu2Oy sample treated in an Au tube and textured in 1.2 T.
[1] A. Lusnikov, L.L. Miller, R.W. McCallum, S. Mitra, W.C. Lee and D.C. Johnson, J. Appl. Phys. 65 (1989) 3136. [2] P. de Rango, M. Lees, P. Lejay, A. Sulpice, R. Tournier, M. lngold, P. Germi and M. Pernet, Nature 349 (1991) 770. [3] C. Hannay, R. Cloots and M. Ausloos, Solid State Commun. 83 (1992) 349.
S. Stassen et al. / Journal of Crystal Growth 166 (1996) 281-285
[4] R. Cloots, A. Rulmont, C. Hannay, P.A. Godelaine, H.W. Vanderschueren, P. R6gnier and M. Ausloos, Appl. Phys. Lett. 61 (1992) 2718. [5] Ch. Laurent, PhD Thesis, University of Liege (1989). [6] S. Stassen, A. Rulmont, T. Krekels, M. Ausloos and R. Cloots, J. Appl. Cryst. 29 (1996) 147.
285
[7] X.F. Zhang, G. Van Tendeloo, S.L. Ge, J.H.P.M. Emmen and V.A.M. Brabers, Physica C 215 (1993) 39. [8] F. Chen, R.S. Markiewicz and B.C. Griessen, in: Superconductivity and Applications, Eds. Hoi S. Kwok, Yi-Han Kao and D.T. Shaw (Plenum, New York, 1989) p. 541.
CRYSTAL O R O W T H
ELSEVIER
Journal of Crystal Growth 166 (1996) 281-285
Texturation of Bi-based 2212 superconducting bulk ceramics S. Stassen
a,*,
A. Vanderschueren
b, R.
Cloots a,b, A. Rulmont
a, M.
Ausloos c,l
a SUPRAS, Chemistry Institute B6, University ofLibge, Sart-Tilman, B-4000 Libge, Belgium b SUPRAS, Montefiore Electricity Institute B28, University ofLibge, Sart-Tilman, B-4000 Libge, Belgium c SUPRAS, Physics Institute B5, University ofLibge, Sart-Tilman, B-4000 Libge, Belgium
Abstract
The magnetic texturing growth (Mag TG) technique has been applied for the first time to 2212 powder (BieSrzCao.sDyo.2Cu20 v) in order to obtain well-textured, Bi-based bulk ceramics. The sample has been analyzed by X-ray diffraction analysis, poiarized light microscopy, scanning electron microscopy, and EDX analysis. Electric resistivity measurements have also been made. A well-textured sample with an intergrowth of two phases was observed: the expected 2212 superconducting phase sandwiching a non-superconducting Bi-rich phase. The electric transition is quite sharp with a Tc around 87 K. Some further experiments in gold and copper tubes have been performed and offer the possibility of providing well-textured coils.
1. Introduction
The best way to obtain superconducting ceramics with good electrical properties such as high critical current density is to texture them. Magnetic texturing growth (Mag TG) is certainly one of the most competitive techniques to achieve such a goal. It has been applied extensively to the YBCO system, often doped by rare-earth ions [1-4]. However, the Mag TG has never been tried on Bi-based systems. In this paper we present for the first time magnetic textured 2212 bulk ceramics. The ceramic is found to be well-textured.
* Corresponding author. i E-mail: [email protected].
2. E x p e r i m e n t a l details
2.1. Textured bulk 2212 ceramics
The synthesis starts by mixing stoichiometric amounts of BieO 3, CaCO 3, SrCO 3, CuCO 3 • Cu(OH) 2 and DyeO 3. The mixture is then treated at 820°C for 48 h at a heating rate of 150°C/h including two intermediate grindings. The resulting crystalline powder Bi2Sr2Ca0.sDY0.zCueOy is then introduced into an alumina crucible and placed in a vertical furnace. A 1.2 T magnetic field is applied horizontally during the whole process. The sample is heated to 950°C at a heating rate of 150°C/h. It is then cooled down to 800°C at 2 ° C / h followed by a 5 0 ° C / h cooling rate to room temperature. The sample is then removed from the alumina crucible in which texturation took place. A zero field run has also been performed as a control procedure.
0022-0248/96/$15.00 Copyright © 1996 Elsevier Science B.V. All rights reserved PII S0022-0248(96)00129-7
282
S. Stassen et al./Journal ~f Co'stal Growth 166 (1996) 281-285
X-ray diffractograms have been recorded with a Siemens D5000 diffractometer usin~ Cu K o~ monochromatized radiation (A = 1.5406 A). Optically polarized light microscopy analysis has been performed on the sample. Optimal color contrast to make visible interesting structural details has been attempted. EDX analysis has been performed on a Cambridge scanning electron microscope (SEM) at the Cockerill Research Center in Liege. The electrical measurements were made with the four-probe technique in an automated set-up [5]. Data were taken from room temperature down to about 40 K.
3. Results and discussion 3.1. Textured bulk 2212 ceramics
Fig. 1 shows the X-ray diffraction patterns recorded for the cross-section perpendicular to the applied magnetic induction direction. The sample treated in the 1.2 T magnetic field is well textured since the (00/) reflection peaks are almost the only ones visible in the diffraction pattern (Fig. lb) and are very much enhanced when compared to the zero-field specimen (Fig. la). A splitting of the (00/) peaks is observed and can be explained by the intergrowth of the so-called N and D phases which we discussed in a previous paper [6]. Those two phases result from the partial substitution of Ca by Dy. They have slightly different c parameters depending on which sites Dy occupies [7]. X-ray diffraction analysis does not show any particular secondary phase.
2.2. Textured wire
The preparation of textured coils follows the same procedure, except for the container which is either a gold or a copper tube closed at one end.
6°1 960
1
(b)
>~ 640-
O
320-
30
4o
~'4
5b
Diffraction angle (°20) (L=1.5406A) Fig. 1. X-ray diffraction patterns of Bi2Sr2Ca0 sDyo 2Cu20,. sample textured in 1.2 T. The observation plane is perpendicular to the applied magnetic field.
S. Stassen et al. / Journal of Crystal Growth 166 (1996) 281-285
The polarized light microscopy pictures (Fig. 2) exhibit a typical textured microstructure. The picture in Fig. 2 (top) has been taken with the observed plane containing the c-axis whereas Fig. 2 (bottom) represents the same sample with ab-planes being the observation plane. The sample is thus well textured with a stacking of large platelets lying along the direction of the applied magnetic field. Magnetic texturing growth orients the sample with the c-axis parallel to the magnetic field direction since Dy is known to be a parallel aligner [8]. EDX analysis has been performed on the surface of the polished sample for the plane containing the c-axis (see Fig. 3) and for which the stacking of ab platelets is visible. EDX analysis confirms the presence of two types of phases. Moreover some copper oxide spots are also visible. The dark grey layers ( # 1, 3, 5, 7 in Fig. 3) are made of regular 2212 material (arrows in Fig. 2). The light grey layers ( #
283
Fig. 3. SEM pictures of Bi2SrzCao.sDyo.2Cu2Oy sample textured in 1.2 T. The c-axis lies in the observation plane.
2, 4, 6, 8 in Fig. 3) are made of phases rich in Bi, sometimes poor in Ca ( # 4 and 6 in Fig. 3), sometimes poor in Cu ( # 2 and 8 in Fig. 3) depending on the presence of copper oxide spots (black phase in Fig. 3) in that layer. Copper oxide crystallizes from the melt to form dendrites or spots during the cooling part of the process. They probably result from an excessive cooling rate. Their formation implies that the neighboring phase from which they arise is poor in copper. In further work, we will try to avoid their formation by lowering the cooling rate. Microscopic and EDX analysis thus reveal the intergrowth of two phases: the expected 2212 superconducting phase sandwiching a non-superconducting Bi-rich phase. Electrical resistivity versus temperature curves are show in Fig. 4 for the cases in which the currents are applied parallel ( I ) or perpendicular ( 0 ) to the magnetic induction direction. The anisotropy of the resistivity curves confirms the texture. The resistivity above T~ is much higher in the c-direction than in the ab-planes. This result is consistent with the fact that the superconducting currents flow in the copper oxide planes. The derivative curves (not shown) of the electrical resistivity exhibit a T~ of about 87 K characteristic of well-connected 2212 materials. 3.2. Textured wire
Fig. 2. Polarized light optical m i c r o s c o p y of Bi~Sr2Ca0.sDY0.zCuzQ sample textured in 1.2 T. (Top) The c-axis lies in the observation plane and is perpendicular to the layers. (Bottom) The observation plane is in the ab-planes.
First, we tried to replace the alumina crucible by a copper tube in order to get a textured superconducting wire. Unfortunately, the high reactivity of copper led to a multiphase system at the interface between the remainder of the tube and the 2212 core.
284
S. Stassen et al. / Journal of Crystal Growth 166 (1996) 281-285 1400
,
,
,
1500 1200 1100 1000 900 800
small transition since at room temperature the resistivity is already very low due to percolation through the Au tube. The resistivity versus temperature curve (Fig. 5) exhibits a typical 2212 " c l e a n " material transition comparable to that observed for the textured material in an alumina container.
7OO 6OO 500
4. Conclusion
400 3OO 2OO tO0 0
!
.
.
75
.
.
.
.
90
105
Temperature (K) Fig. 4. Electrical resistivity p versus temperature of Bi2Sr2Ca0.8Dy0.2Cu2Oy sample textured in 1.2 T for cases in which the current is applied parallel ( I ) or perpendicular (O) to the magnetic field direction.
We have thus decided to make a new attempt with a more inert material such as a gold tube. That experiment was successful and no interfacial secondary reaction took place. The superconducting 2212 material was then removed from the Au tube to be analyzed and measured. Resistivity measurement on the entire system after the Au wrapping had been removed gives only a
8
. . . .
i
. . . .
t
. . . .
i
. . . .
i
. . . .
v
This magnetic texturing growth technique offers an easy route to synthesize textured 2212 bulk ceramics with good anisotropic properties. The sample is made of two phases: the expected 2212 superconducting phase sandwiching a non-superconducting Bi-rich phase. The splitting of the (00l) reflection peaks is observed and is explained by the intergrowth of N and D phases with two different c parameters. An application of this technique offers the possibility of producing a well-textured wire.
Acknowledgements R.C. and S.S. are particularly grateful to the FNRS for a research grant. This work is part of the S U P R A N A T S U / 0 2 / 1 3 Superconductivity Impulse Program of the Services for Scientific, Technical and Cultural (SSTC) Affairs. An ARC (64-99/174) grant from the Ministry of Higher Education through the University of Liege Research Council is also acknowledged. The authors are grateful to Professor H.W. Vanderschueren for allowing them to use the MIEL laboratory and to Dr. M. Michellini at the Cockerill Research Center for the EDX facilities.
2
References 60
70
80
90
100
10
T e m p e r a t u r e (K) Fig. 5. Electrical resistivity p versus temperature of Bi2Sr2CaosDyo2Cu2Oy sample treated in an Au tube and textured in 1.2 T.
[1] A. Lusnikov, L.L. Miller, R.W. McCallum, S. Mitra, W.C. Lee and D.C. Johnson, J. Appl. Phys. 65 (1989) 3136. [2] P. de Rango, M. Lees, P. Lejay, A. Sulpice, R. Tournier, M. lngold, P. Germi and M. Pernet, Nature 349 (1991) 770. [3] C. Hannay, R. Cloots and M. Ausloos, Solid State Commun. 83 (1992) 349.
S. Stassen et al. / Journal of Crystal Growth 166 (1996) 281-285
[4] R. Cloots, A. Rulmont, C. Hannay, P.A. Godelaine, H.W. Vanderschueren, P. R6gnier and M. Ausloos, Appl. Phys. Lett. 61 (1992) 2718. [5] Ch. Laurent, PhD Thesis, University of Liege (1989). [6] S. Stassen, A. Rulmont, T. Krekels, M. Ausloos and R. Cloots, J. Appl. Cryst. 29 (1996) 147.
285
[7] X.F. Zhang, G. Van Tendeloo, S.L. Ge, J.H.P.M. Emmen and V.A.M. Brabers, Physica C 215 (1993) 39. [8] F. Chen, R.S. Markiewicz and B.C. Griessen, in: Superconductivity and Applications, Eds. Hoi S. Kwok, Yi-Han Kao and D.T. Shaw (Plenum, New York, 1989) p. 541.