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High-field magnetization of MSTG processed YBa2Cu3O7
Solid State Communications, Vol. 81, No. 10, pp. 863-865, 1992. Printed in Great Britain.
0038-1098/92 $5.00 + .00 Pergamon Press plc
HIGH-FIELD MAGNETIZATION OF MSTG PROCESSED YBa2Cu307 Y.C. Chuang, G.F. Zhou, J.P. Liu and G.W. Qiao Institute of Metal Research, Academia Sinica, Shenyang 110015, People's Republic of China and J.N. Li, X. Li, F.R. de Boer and J.J.M. Franse Van der Waals-Zeeman Laboratorium, Universiteit van Amsterdam, Valckenierstraat 65, 1018 XE Amsterdam, The Netherlands
(Received 1 July 1991 by G. Fasol) Textured YBa2Cu307 samples were prepared by the Melt Spun Texture Growth (MSTG) process. Magnetization measurements have been performed at 4.2 K in magnetic fields up to 38 T, applied parallel and perpendicular to the preferential growth direction. The critical current densities are deduced from the irreversible magnetization and the pinning forces have been evaluated.
1. INTRODUCTION SINCE THE discovery of YBa2Cu307 with a superconducting transition temperature above the boiling point of liquid nitrogen, tremendous efforts have been made world wide to make the material suitable for practical use. Unfortunately, most applications are hampered by the low critical current density which is believed to be attributable to the presence of weak links in these oxide superconductors [1,2]. It is well established that one of the most promising methods to overcome weak links in these materials is by unidirectional growth of the superconducting phase [3-7]. Textured YBa2Cu307 samples have been prepared by the MSTG (Melt Spun Texture Growth) process [7]. The irreversible magnetization has been measured at 4.2 K in fields applied parallel and perpendicular to the preferential growth direction. 2. EXPERIMENTAL DETAILS For the preparation of textured YBa2Cu307 samples, appropriate amounts of mixtures of Y203, BaCO 3 and CuO were sintered for 24 h at 950°C in oxygen flow. The sintered powders were pressed into pellets and induction heated to 1400°C for 3 to 5 min. The melt (Y203 + L) was rapidly ejected onto a rotating copper roller. In this way, strips with finely and homogeneously dispersed Y203 were obtained. The strips were reheated to 1100°C (211 + L region) and maintained at this temperature for 20min to allow for the formation of the 2 1 1 phase by a peritectic reaction. After this, the strips were quickly cooled
to 1000°C, followed by cooling at a rate fo l°Ch t to 950°C in a tube furnace with appropriate thermal gradient during which the tetragonal 1 2 3 phase was produced by another peritectic reaction of the 2 1 1 phase. Upon further furnace cooling to 500-600°C and maintaining at this temperature for 4-6h in an oxygen flow, a transition of the tetragonal 1 2 3 phase to the orthorhombic 1 2 3 phase took place. The samples were then cooled slowly to room temperature. A more detailed description of the MSTG-process has been presented in [7]. The textured YBa2Cu307 samples were checked by X-ray diffraction to be single phase and their superconducting-transition temperatures were determined by a.c. susceptibility measurements. Two samples with a total mass of 41.4 mg aligned with their c-axes parallel and two other samples with a total mass of 26.8 mg with their a-b planes parallel, served as the samples for the magnetization measurements with the field applied parallel to the c-axis and to the ab-plane, respectively. The dimensions of the YBa2Cu307 samples were carefully measured under a microscope. The magnetization measurements were performed in the 40 T facility of the University of Amsterdam with the samples immersed in liquid helium. Triangular field versus time profiles were employed with increasing- and decreasing-field rates of 42 T s- ~for measurements up to 11, 15, 22 and 29 T. The 38 T experiment was performed with an increasing-field rate of 140 T s and a decreasing-field rate of 54 T s ~. The samples were heated to room temperature after each pulse in order to remove the trapped flux.
863
864
H I G H - F I E L D M A G N E T I Z A T I O N OF M S T G
Vol. 81, No. 10
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3. RESULTS A N D DISCUSSION The SEM micrograph of a fractured surface of a textured YBa2Cu307 sample and the X-ray diffraction pattern of cleavage plane are shown in Figs. 1 and 2, respectively. It can be seen that the sample has dense layer-structure with regular alignment, and that the (0 0 1) planes are always parallel to the growth direction indicating that the crystals are preferentially aligned. Figure 3 shows the temperature dependence of the a.c. susceptibility for a MSTG-processed YBazCu307 sample, the superconducting onset temperature being about 91 K. The magnetization curves at 4.2K of MSTGprocessed YBazCu307 with B !] c and B 2_ c are shown in Fig. 4. In both cases, the irreversible magnetization persists up to the maximum field of 38 T, although the hysteresis declines gradually with increasing magnetic field. In addition, heating effects due to flux-flow during a field pulse are observed in the polycrystalline MSTG samples, which was also observed earlier in
,o (D
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ts
ioo
i J!
i
_Jl _ j i L j , ~ y 10
20
t,o
ill i i _ 2 \ •_J'".
-q"
30
50
60
20
Fig. 2. X-ray diffraction pattern of cleavage plane in textured YBa2Cu307 demonstrating the crystal to be preferentially aligned.
i
g 8
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Fig. !. SEM micrograph of a fracture surface of a textured YBa2 Cu3 0 7 •
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. . . . 50
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~50
200
250
300
Fig. 3. Temperature dependence of the a.c. susceptibility for MSTG-processed YBa2 Cu307. single-crystalline YBCO sample [9]. It is clearly seen that there is some difference in the magnetization values for the different field vs time profiles. For instance, although the same field-sweep rate was used, the magnetization values in a 22 T pulse are slightly larger than those in a 29 T pulse, which implies that in the latter case the field is applied during a longer time. The magnetization values in a 22T pulse are also slightly larger than those in a 38 T pulse. In this case the field-duration times are almost the same but for the 38T pulse the field-sweep rate is larger. These differences provide evidence for heating effects. The Bean model was used to determine the critical current density [8]. Within this model magnetic moment is proportional to the critical current. Starting with the Bean model, the critical current density J, can easily be related to the difference AM of the magnetic moment between the field-up and field-down curve: J, = AM/E~ V~di, where V, is the volume of the textured sample i and d~ is an effective length that depends on the orientation of the sample. For the field parallel to the c-axis, d, = (41jbi/97r) j/2, for the field perpendicular to the c-axis, d~ = hi/2. Here, l,, b, and hi are the length, width and height of the samples, respectively. The critical current densities at 4.2 K have been calculated in this way and are shown in Fig. 5. It can be seen that the critical current density slightly decreases with increasing magnetic field. For the field parallel to the growth direction (B 2_ c), even at 38 T, the critical current density J, at 4.2 K is still well above 2.5 x 108 A m -2. This value is comparable with that obtained for single-crystalline YBa2Cu307 [9]. The volume density of the pinning force Fp can be deduced by means of the formula Fp = J~ × B. The pinning force of MSTG-processed YBa2Cu307 is shown in Fig. 6 for the fields parallel to the c-axis and within the ab-plane at 4.2 K. In both cases, the pinning
Vol. 81, No. 10
HIGH-FIELD MAGNETIZATION OF MSTG I
30-
E
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I
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a
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YBa2gu307
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Fig. 4. Magnetization curves with various field vs time profiles for (a) B II c and (b) B _Lc. The 11, 15, 22 and 29 T experiments are with increasing- and decreasing-field rates of 42 T s-l; the 38 T experiments with an increasing-field rate of 140 T s-' and a decreasing-field rate of 54 T s-l 8.0
I
I
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YBa2Cu307
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YBa2Cu307
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Fig. 5. Field-dependence of the critical current density of MSTG-processed YBasCu307 at 4.2 K for B l[ c and B±c. forces increase with increasing field, and reach a maximum at approximately 35T. With the field applied parallel to the growth direction (B ± c), the pinning force at 35T exceeds 101°Nm 3. This value is ten times larger than the peak value of the pinning force in sintered YBasCu307 [10]. This is due to the improvement of the intergrain weak link and the effective pinning by the 2 1 1 particles well-distributed in the i 2 3 phase in the MSTG sample.
Acknowledgements - This work has been carried out within the scientific exchange between China and the Netherlands and has been partly supported by the Chinese National Center of Research and Development of Superconductivity.
20
30
40
(TI
Fig. 6. The pinning force of MSTG-processed YBa 2Cu307 at 4.2 K for B IIc and B ± c.
2. 3. 4. 5. 6. 7. 8. 9.
REFERENCES 10. J. Ekin, A. Braginski, A. Panson, M. Janocko, D. Capone, N. Zaluzec, B. Flandermeyer, O. de
lO
B
(T)
Lima, M. Hong, J. Kwo & S. Liou, J. Appl. Phys. 62, 4821 (1987). J. Ekin, Adv. Ceramic Mater. 2, 586 (1987). D. Dimos, P. Chaudhari, J. Mannhart & F. Legoues, Phys. Rev. Lett. 61, 219 (1988). S. Jin, T. Tiefel, R. Sherwood, R. Van Dover, M. Davis, G. Kammlott, R. Fastnacht & H. Keith, Phys. Rev. B37, 7850 (1988). K. Salama, V. Selvamanickam, L. Gao & K. Sun, Appl. Phys. Lett. 54, 2352 (1989). P.J. McGinn, W. Chen, N. Zhu, U. Balachomdran & M.T. Lanagan, Physica C165, 480 (1990). G.F. Zhou, G. W. Qiao, J.G. Huang, M. Jiang, Y.Z. Wang & Y.C. Chuang, J. Crystal Growth, in press (1991). C.P. Bean, Rev. Phys. Rev. Lett. 8, 250 (1962). J.N. Li, F.R. de Boer, L.W. Roeland, M.J.V. Menken, K. Kadowaki, A.A. Menovsky & J.J.M. Franse, Physica C169, 81 (1990). G.F. Zhou, X. Li, F.R. de Boer, G.W. Qiao & Y.C. Chuang, Physica B, accepted for publication (1991).
0038-1098/92 $5.00 + .00 Pergamon Press plc
HIGH-FIELD MAGNETIZATION OF MSTG PROCESSED YBa2Cu307 Y.C. Chuang, G.F. Zhou, J.P. Liu and G.W. Qiao Institute of Metal Research, Academia Sinica, Shenyang 110015, People's Republic of China and J.N. Li, X. Li, F.R. de Boer and J.J.M. Franse Van der Waals-Zeeman Laboratorium, Universiteit van Amsterdam, Valckenierstraat 65, 1018 XE Amsterdam, The Netherlands
(Received 1 July 1991 by G. Fasol) Textured YBa2Cu307 samples were prepared by the Melt Spun Texture Growth (MSTG) process. Magnetization measurements have been performed at 4.2 K in magnetic fields up to 38 T, applied parallel and perpendicular to the preferential growth direction. The critical current densities are deduced from the irreversible magnetization and the pinning forces have been evaluated.
1. INTRODUCTION SINCE THE discovery of YBa2Cu307 with a superconducting transition temperature above the boiling point of liquid nitrogen, tremendous efforts have been made world wide to make the material suitable for practical use. Unfortunately, most applications are hampered by the low critical current density which is believed to be attributable to the presence of weak links in these oxide superconductors [1,2]. It is well established that one of the most promising methods to overcome weak links in these materials is by unidirectional growth of the superconducting phase [3-7]. Textured YBa2Cu307 samples have been prepared by the MSTG (Melt Spun Texture Growth) process [7]. The irreversible magnetization has been measured at 4.2 K in fields applied parallel and perpendicular to the preferential growth direction. 2. EXPERIMENTAL DETAILS For the preparation of textured YBa2Cu307 samples, appropriate amounts of mixtures of Y203, BaCO 3 and CuO were sintered for 24 h at 950°C in oxygen flow. The sintered powders were pressed into pellets and induction heated to 1400°C for 3 to 5 min. The melt (Y203 + L) was rapidly ejected onto a rotating copper roller. In this way, strips with finely and homogeneously dispersed Y203 were obtained. The strips were reheated to 1100°C (211 + L region) and maintained at this temperature for 20min to allow for the formation of the 2 1 1 phase by a peritectic reaction. After this, the strips were quickly cooled
to 1000°C, followed by cooling at a rate fo l°Ch t to 950°C in a tube furnace with appropriate thermal gradient during which the tetragonal 1 2 3 phase was produced by another peritectic reaction of the 2 1 1 phase. Upon further furnace cooling to 500-600°C and maintaining at this temperature for 4-6h in an oxygen flow, a transition of the tetragonal 1 2 3 phase to the orthorhombic 1 2 3 phase took place. The samples were then cooled slowly to room temperature. A more detailed description of the MSTG-process has been presented in [7]. The textured YBa2Cu307 samples were checked by X-ray diffraction to be single phase and their superconducting-transition temperatures were determined by a.c. susceptibility measurements. Two samples with a total mass of 41.4 mg aligned with their c-axes parallel and two other samples with a total mass of 26.8 mg with their a-b planes parallel, served as the samples for the magnetization measurements with the field applied parallel to the c-axis and to the ab-plane, respectively. The dimensions of the YBa2Cu307 samples were carefully measured under a microscope. The magnetization measurements were performed in the 40 T facility of the University of Amsterdam with the samples immersed in liquid helium. Triangular field versus time profiles were employed with increasing- and decreasing-field rates of 42 T s- ~for measurements up to 11, 15, 22 and 29 T. The 38 T experiment was performed with an increasing-field rate of 140 T s and a decreasing-field rate of 54 T s ~. The samples were heated to room temperature after each pulse in order to remove the trapped flux.
863
864
H I G H - F I E L D M A G N E T I Z A T I O N OF M S T G
Vol. 81, No. 10
2 0
L ©
--2
>. o
~ E1 ua~ u3
3. RESULTS A N D DISCUSSION The SEM micrograph of a fractured surface of a textured YBa2Cu307 sample and the X-ray diffraction pattern of cleavage plane are shown in Figs. 1 and 2, respectively. It can be seen that the sample has dense layer-structure with regular alignment, and that the (0 0 1) planes are always parallel to the growth direction indicating that the crystals are preferentially aligned. Figure 3 shows the temperature dependence of the a.c. susceptibility for a MSTG-processed YBazCu307 sample, the superconducting onset temperature being about 91 K. The magnetization curves at 4.2K of MSTGprocessed YBazCu307 with B !] c and B 2_ c are shown in Fig. 4. In both cases, the irreversible magnetization persists up to the maximum field of 38 T, although the hysteresis declines gradually with increasing magnetic field. In addition, heating effects due to flux-flow during a field pulse are observed in the polycrystalline MSTG samples, which was also observed earlier in
,o (D
'I
ts
ioo
i J!
i
_Jl _ j i L j , ~ y 10
20
t,o
ill i i _ 2 \ •_J'".
-q"
30
50
60
20
Fig. 2. X-ray diffraction pattern of cleavage plane in textured YBa2Cu307 demonstrating the crystal to be preferentially aligned.
i
g 8
g' -~o
Fig. !. SEM micrograph of a fracture surface of a textured YBa2 Cu3 0 7 •
",1ST G YBa2Cu3O 7
o
. . . . 50
~00
~50
200
250
300
Fig. 3. Temperature dependence of the a.c. susceptibility for MSTG-processed YBa2 Cu307. single-crystalline YBCO sample [9]. It is clearly seen that there is some difference in the magnetization values for the different field vs time profiles. For instance, although the same field-sweep rate was used, the magnetization values in a 22 T pulse are slightly larger than those in a 29 T pulse, which implies that in the latter case the field is applied during a longer time. The magnetization values in a 22T pulse are also slightly larger than those in a 38 T pulse. In this case the field-duration times are almost the same but for the 38T pulse the field-sweep rate is larger. These differences provide evidence for heating effects. The Bean model was used to determine the critical current density [8]. Within this model magnetic moment is proportional to the critical current. Starting with the Bean model, the critical current density J, can easily be related to the difference AM of the magnetic moment between the field-up and field-down curve: J, = AM/E~ V~di, where V, is the volume of the textured sample i and d~ is an effective length that depends on the orientation of the sample. For the field parallel to the c-axis, d, = (41jbi/97r) j/2, for the field perpendicular to the c-axis, d~ = hi/2. Here, l,, b, and hi are the length, width and height of the samples, respectively. The critical current densities at 4.2 K have been calculated in this way and are shown in Fig. 5. It can be seen that the critical current density slightly decreases with increasing magnetic field. For the field parallel to the growth direction (B 2_ c), even at 38 T, the critical current density J, at 4.2 K is still well above 2.5 x 108 A m -2. This value is comparable with that obtained for single-crystalline YBa2Cu307 [9]. The volume density of the pinning force Fp can be deduced by means of the formula Fp = J~ × B. The pinning force of MSTG-processed YBa2Cu307 is shown in Fig. 6 for the fields parallel to the c-axis and within the ab-plane at 4.2 K. In both cases, the pinning
Vol. 81, No. 10
HIGH-FIELD MAGNETIZATION OF MSTG I
30-
E
<~
I
I
•
a
30
-
-
MSTG
_
i
YBa2gu307
B//C
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K
~
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-
~ - - ~
YBa2Cu3D7
E
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--
~ F
MSTG
~
•
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20 B
30
40
J ----
'
.I 20
0
,
[T]
I __ 20 B
,
i 30
,
t 40
[T]
Fig. 4. Magnetization curves with various field vs time profiles for (a) B II c and (b) B _Lc. The 11, 15, 22 and 29 T experiments are with increasing- and decreasing-field rates of 42 T s-l; the 38 T experiments with an increasing-field rate of 140 T s-' and a decreasing-field rate of 54 T s-l 8.0
I
I
I
:12MSTG
YBa2Cu307
4,2
K
MSTG
YBa2Cu307
4
2
K
d ooaaa°ua~°°
~
oJ E
m
O
ab-plane a B // c-axls
6.0
a B II
:10 DO E
"Z
o
o B // ai0-pl~ne -
~ B //
~aou°t~
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8
=~ °°
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0.0 0
l
,
I
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~
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30
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0
40
Fig. 5. Field-dependence of the critical current density of MSTG-processed YBasCu307 at 4.2 K for B l[ c and B±c. forces increase with increasing field, and reach a maximum at approximately 35T. With the field applied parallel to the growth direction (B ± c), the pinning force at 35T exceeds 101°Nm 3. This value is ten times larger than the peak value of the pinning force in sintered YBasCu307 [10]. This is due to the improvement of the intergrain weak link and the effective pinning by the 2 1 1 particles well-distributed in the i 2 3 phase in the MSTG sample.
Acknowledgements - This work has been carried out within the scientific exchange between China and the Netherlands and has been partly supported by the Chinese National Center of Research and Development of Superconductivity.
20
30
40
(TI
Fig. 6. The pinning force of MSTG-processed YBa 2Cu307 at 4.2 K for B IIc and B ± c.
2. 3. 4. 5. 6. 7. 8. 9.
REFERENCES 10. J. Ekin, A. Braginski, A. Panson, M. Janocko, D. Capone, N. Zaluzec, B. Flandermeyer, O. de
lO
B
(T)
Lima, M. Hong, J. Kwo & S. Liou, J. Appl. Phys. 62, 4821 (1987). J. Ekin, Adv. Ceramic Mater. 2, 586 (1987). D. Dimos, P. Chaudhari, J. Mannhart & F. Legoues, Phys. Rev. Lett. 61, 219 (1988). S. Jin, T. Tiefel, R. Sherwood, R. Van Dover, M. Davis, G. Kammlott, R. Fastnacht & H. Keith, Phys. Rev. B37, 7850 (1988). K. Salama, V. Selvamanickam, L. Gao & K. Sun, Appl. Phys. Lett. 54, 2352 (1989). P.J. McGinn, W. Chen, N. Zhu, U. Balachomdran & M.T. Lanagan, Physica C165, 480 (1990). G.F. Zhou, G. W. Qiao, J.G. Huang, M. Jiang, Y.Z. Wang & Y.C. Chuang, J. Crystal Growth, in press (1991). C.P. Bean, Rev. Phys. Rev. Lett. 8, 250 (1962). J.N. Li, F.R. de Boer, L.W. Roeland, M.J.V. Menken, K. Kadowaki, A.A. Menovsky & J.J.M. Franse, Physica C169, 81 (1990). G.F. Zhou, X. Li, F.R. de Boer, G.W. Qiao & Y.C. Chuang, Physica B, accepted for publication (1991).