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Effects of cooling rate on single domain growth and the superconducting properties for YBCO bulk
Physica C 386 (2003) 262–265 www.elsevier.com/locate/physc
Effects of cooling rate on single domain growth and the superconducting properties for YBCO bulk L. Xiao *, H.T. Ren, Y.L. Jiao, M.H. Zheng, Y.X. Chen General Research Institute for Nonferrous Metals, No. 2 Xinjiiekouwai St., Beijing 100088, China
Abstract A series of YBCO single domain samples were prepared by using the top seeded melt growth method with different cooling rate during the melt processing. For all of the samples, the DC magnetization and the levitation force were measured to determine the effects of cooling rate on the critical transition temperature Tc magnetization critical current density Jcm and levitation force F . The results indicate the influence of cooling rate on superconducting properties is very strong and the cooling rate has an optimum range. For instance, the rates of 0.9–1.1 °C/h are suitable for the sample with 11 mm in diameter, above which single domain size becomes small and below which the superconducting properties degrade obviously. The similar result has been also observed for the sample with 30 mm in diameter. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 74.72.Bk; 74.80.Bj; 74.62.Bf Keywords: YBCO; Single domain; Cooling rate; Superconducting properties
1. Introduction A large number of studies have been performed on the fabrication of YBCO single domain disk by using the top seeded melt growth method. The melt growth was carried out under the condition of the slow cooling with and without temperature gradient, or holding for a long time under the isothermal condition. The former has been widely employed to grow single domain YBCO sample [1–5]. In this process, the slow cooling rate is a crucial parameter for the texture growth. In general, the slow cooling rates of 0.2–1.0 °C/h were used because the growth rate of Y-123 crystal was very low. For example, a rate of 0.3 °C/h was used *
Corresponding author. Fax: +86-10-62376971. E-mail address: [email protected] (L. Xiao).
in a temperature range of about 30 °C to grow single domain sample with 30 mm in diameter [6], which means a long processing time of about one hundred hours should be used. The slower cooling rate of 0.16 °C/h was used for the growth of the sample with 93 mm in diameter, it corresponds to processing time of the several hundred hours [1]. In order to shorten the time of melt processing, on the premise of the single domain and high superconducting properties, the cooling rate should be optimized. In this paper, we report some of the experimental results of the different cooling rates.
2. Experimental Y1:8 Ba2:4 Cu3:4 O7 d precursor powder was prepared through the solid-state reacting method.
0921-4534/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0921-4534(02)02163-9
L. Xiao et al. / Physica C 386 (2003) 262–265
After Pt of 0.2 wt.% was doped, the powder was uni-axially pressed into cylindrical precursor pellets with 13 mm in diameter and 35 mm in diameter. SmBaCuO seed was placed on the upper surface of YBCO sample before melt processing. The sample of 13 mm in diameter was heated to 1045 °C and held for 20 min to melt partially and then was rapidly cooled down to 1008 °C, which was the starting temperature of slow cooling stage, then was cooled slowly to 990 °C at different rates of 0.2, 0.3, 0.5, 0.75, 0.9, 1.0, 1.1, 1.3 and 1.5 °C/h. Finally, samples were cooled down to room temperature. While the precursor samples with 35 mm in diameter were held at 1045 °C for 1.5 h and cooled slowly from 1010 to 975 °C at a rate of 0.2, 0.3, 0.33 and 0.5 °C/h, respectively. The final sizes of samples are 11 and 30 mm in diameter. For all of the samples the post annealing was performed under the oxygen pressure of about 1 MPa at 470 °C for 72 h. The levitation force was measured by using NdFeB magnet with 10 mm in diameter and the surface magnetic field of 0.4 T for YBCO sample of 11 mm in diameter, while the magnet with 26 mm diameter and field of 0.5 T was used for the sample of 30 mm diameter. The temperature dependence of DC magnetization and the magnetic hysteresis loop at 77 K were measured by using a SQUID magnetometer. The measured thin disk samples with 4.4 mm in diameter and 0.5 mm thickness were cut from the above measured samples. Magnetic field was applied parallel to caxis of sample. Jcm was estimated from magnetic hysteresis loops applying the modified Bean critical state model [7].
263
Fig. 1. Top surface views for samples prepared at different cooling rates of (a) 0.3 °C/h and (b) 1.3 °C/h.
observed as shown in Fig. 1b, and the size of single domain reduced with cooling rate increasing. For a given temperature range of 18 °C, the samples grown at different cooling rates appear different cross section views. Fig. 2a presents a schematic diagram for the sample of 0.3 °C/h, which displays a unitary c-axis orientation and the c-axis is vertical to the surface of sample. For the samples grown at the cooling rate above 0.5 °C/h, the unitary c-axis oriented region reduces with the cooling rate increasing. For example, the region does not reach the bottom for the sample at a cooling rate of 1.0 °C/h as shown in Fig. 2b. The above-mentioned results mean that the slower cooling rate, the more beneficial for the single domain growth. In addition, the cooling rate being faster than the crystal growth rate could cause the imperfect single domain. As viewed from the single domain growth only, it is considered that the cooling rate of 0.2 or 0.3 °C/h is the best. Fig. 3 shows the relationship between the normalized DC magnetization and the temperature. It
3. Results and discussion Two photos of the top surface view for samples with 11 mm in diameter are shown in Fig. 1. It is obvious that the cooling rate affects the size of single domain. A perfect single domain sample was prepared at a cooling rate of 0.3 °C/h, as seen in Fig. 1a. The same top surface views were also obtained for the samples grown at different cooling rates of 0.2–1.1 °C/h. When the cooling rate was larger than 1.3 °C/h, a small single domain was
Fig. 2. Schematic diagrams of the cross section for samples prepared at different cooling rates of (a) 0.3 °C/h and (b) 1.1 °C/h.
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L. Xiao et al. / Physica C 386 (2003) 262–265
30
0.0
Normalized M
-0.4 -0.6
Jcm (KA/cm2)
1.3 C/h O 1.1 C/h O 1.0 C/h 0.75OC/h O 0.5 C/h 0.3 OC/h
-0.2
1.3 OC/h 1.1 OC/h 1.0 OC/h 0.75OC/h 0.5 OC/h 0.3 OC/h
25
O
-0.8
20 15 10 5
-1.0
0 60
70
80
90
100
110
0.0
T (K)
can be seen in this figure, Tc;onset drops and DT becomes wide obviously with the cooling rate decreasing. As shown in Fig. 4, Tc;onset is almost changeless when the cooling rate is above 1.0 °C/h, and it decreases rapidly when the cooling rate is below 0.5 °C/h, especially for the sample of 0.2 °C/ h Tc;onset drops below 77 K. Fig. 5 shows the curves of the magnetization critical current density Jcm at 77 K versus applied magnetic field for the samples grown at different cooling rates. It is obviously that the Jcm characteristic is the best for the sample of 1.0 °C/h and it has the peak effect. Fig. 6 reveals the relationship between Jcm and the cooling rate, from which we can see the Jcm value is high at the cooling rate range from 0.9 to 1.3 °C/h. However, the Jcm de-
1.0
1.5
2.0
2.5
3.0
B (T) Fig. 5. Dependence of the magnetization critical current density Jcm on B for different cooling rate.
16
Jcm (kA/cm2)
Fig. 3. Dependence of normalized magnetization M on temperature T for different cooling rate.
0.5
Sample:Φ11 mm T : 77 K
12 8 4 0 0.3
0.6
0.9
1.2 O
Cooling rate ( C/h) Fig. 6. Dependence of the magnetization critical current density Jcm on cooling rate at 77 K.
95
Tc, onset
90 85 80
sample:Φ11 mm
75 70
0.2
0.4
0.6
0.8
1.0
1.2
O
Cooling rate ( C/h) Fig. 4. Dependence of Tc;onset on cooling rate.
1.4
creases obviously when the cooling rate is below 0.75 °C/h, it is about one order of magnitude lower for 0.5 °C/h than 1.0 °C/h. The result of the Jcm is in agreement with that of Tc . The measured result of levitation force provides further evidence that the influence of the cooling rate on the superconducting properties of the sample is very strong. As shown in Fig. 7, the maximum f0 value was obtained for the sample with 11 mm in diameter grown at the cooling rate of 1.0 °C/h. With increasing the sample size, the cooling rate corresponding to the maximum value of f0 shifts to the lower, which is about 0.3 °C/h for the sample with 30 mm in diameter.
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indicate that cooling rate has an optimum range, which is 0.9–1.1 °C/h for sample with 11 mm in diameter. It shifts to the lower with the sample size increasing, about 0.3 °C/h is suitable for the sample with 30 mm in diameter. The sample grown at this cooling rate not only has single domain structure and higher Tc , Jcm as well as the levitation force f0 but also shorten processing time greatly which is beneficial to reduce manufacturing expenses. Acknowledgements Fig. 7. Relationship between the cooling rate and the levitation force density at zero distance.
According to above-mentioned results, the cooling rates of 0.9–1.1 °C/h are suitable to obtain better single domain and higher Tc , Jc and f0 for the sample with 11 mm in diameter. For a given temperature range of 18 °C during the crystalgrowth, the cooling rates of 0.2 and 1.0 °C/h correspond to the time of 90 and 18 h, respectively. Therefore, the single domain sample grown at the cooling rate of about 1.0 °C/h not only shortened greatly processing time but also exhibited the higher superconducting properties compared with the others.
4. Conclusions The influences of the cooling rate on the single domain growth and the superconducting properties have been studied. The experimental results
This work was supported by the National Center for Research and Development of Superconductivity (Projects of 863 and 973). References [1] R. Tournier, E. Beaugnon, O. Belmont, X. Chaud, D. Bourgault, D. Lsfort, L. Porcar, P. Tixador, Supercond. Sci. Technol. 13 (2000) 886. [2] D. Lizkendorf, T. Habisreuther, M. Wu, T. Strasser, M. Zeisberger, W. Gawalek, M. Helbig, P. Gornert, Mater. Sci. Eng. B 53 (1998) 75. [3] M. Ullrich, H. Walter, A. Leenders, H.C. Freyhardt, Physica C 311 (1999) 86–92. [4] J.C.L. Chow, L. Wai, C.D. Dewhurst, H.-T. Leuug, D.A. Cardwell, Y.H. Shi, Supercond. Sci. Technol. 10 (1997) 435. [5] H.T. Ren, L. Xiao, Y.L. Jiao, S.A. Chang, X.H. Wang, Y.L. Wang, Physica C 282–287 (1997) 485. [6] L. Xiao, H.T. Ren, Y.L. Jiao, M.H. Zheng, Y.X. Chen, ISMAGLEV (2002) Chengdu of China, submitted for publication. [7] A. Umezawa, G.W. Crabtree, J.Z. Liu, H.W. Weber, W.K. Kwok, L.H. Nunez, T.J. Moran, C.H. Sowers, H. Claus, Phys. Rev. B 36 (1987) 7151.
Effects of cooling rate on single domain growth and the superconducting properties for YBCO bulk L. Xiao *, H.T. Ren, Y.L. Jiao, M.H. Zheng, Y.X. Chen General Research Institute for Nonferrous Metals, No. 2 Xinjiiekouwai St., Beijing 100088, China
Abstract A series of YBCO single domain samples were prepared by using the top seeded melt growth method with different cooling rate during the melt processing. For all of the samples, the DC magnetization and the levitation force were measured to determine the effects of cooling rate on the critical transition temperature Tc magnetization critical current density Jcm and levitation force F . The results indicate the influence of cooling rate on superconducting properties is very strong and the cooling rate has an optimum range. For instance, the rates of 0.9–1.1 °C/h are suitable for the sample with 11 mm in diameter, above which single domain size becomes small and below which the superconducting properties degrade obviously. The similar result has been also observed for the sample with 30 mm in diameter. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 74.72.Bk; 74.80.Bj; 74.62.Bf Keywords: YBCO; Single domain; Cooling rate; Superconducting properties
1. Introduction A large number of studies have been performed on the fabrication of YBCO single domain disk by using the top seeded melt growth method. The melt growth was carried out under the condition of the slow cooling with and without temperature gradient, or holding for a long time under the isothermal condition. The former has been widely employed to grow single domain YBCO sample [1–5]. In this process, the slow cooling rate is a crucial parameter for the texture growth. In general, the slow cooling rates of 0.2–1.0 °C/h were used because the growth rate of Y-123 crystal was very low. For example, a rate of 0.3 °C/h was used *
Corresponding author. Fax: +86-10-62376971. E-mail address: [email protected] (L. Xiao).
in a temperature range of about 30 °C to grow single domain sample with 30 mm in diameter [6], which means a long processing time of about one hundred hours should be used. The slower cooling rate of 0.16 °C/h was used for the growth of the sample with 93 mm in diameter, it corresponds to processing time of the several hundred hours [1]. In order to shorten the time of melt processing, on the premise of the single domain and high superconducting properties, the cooling rate should be optimized. In this paper, we report some of the experimental results of the different cooling rates.
2. Experimental Y1:8 Ba2:4 Cu3:4 O7 d precursor powder was prepared through the solid-state reacting method.
0921-4534/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0921-4534(02)02163-9
L. Xiao et al. / Physica C 386 (2003) 262–265
After Pt of 0.2 wt.% was doped, the powder was uni-axially pressed into cylindrical precursor pellets with 13 mm in diameter and 35 mm in diameter. SmBaCuO seed was placed on the upper surface of YBCO sample before melt processing. The sample of 13 mm in diameter was heated to 1045 °C and held for 20 min to melt partially and then was rapidly cooled down to 1008 °C, which was the starting temperature of slow cooling stage, then was cooled slowly to 990 °C at different rates of 0.2, 0.3, 0.5, 0.75, 0.9, 1.0, 1.1, 1.3 and 1.5 °C/h. Finally, samples were cooled down to room temperature. While the precursor samples with 35 mm in diameter were held at 1045 °C for 1.5 h and cooled slowly from 1010 to 975 °C at a rate of 0.2, 0.3, 0.33 and 0.5 °C/h, respectively. The final sizes of samples are 11 and 30 mm in diameter. For all of the samples the post annealing was performed under the oxygen pressure of about 1 MPa at 470 °C for 72 h. The levitation force was measured by using NdFeB magnet with 10 mm in diameter and the surface magnetic field of 0.4 T for YBCO sample of 11 mm in diameter, while the magnet with 26 mm diameter and field of 0.5 T was used for the sample of 30 mm diameter. The temperature dependence of DC magnetization and the magnetic hysteresis loop at 77 K were measured by using a SQUID magnetometer. The measured thin disk samples with 4.4 mm in diameter and 0.5 mm thickness were cut from the above measured samples. Magnetic field was applied parallel to caxis of sample. Jcm was estimated from magnetic hysteresis loops applying the modified Bean critical state model [7].
263
Fig. 1. Top surface views for samples prepared at different cooling rates of (a) 0.3 °C/h and (b) 1.3 °C/h.
observed as shown in Fig. 1b, and the size of single domain reduced with cooling rate increasing. For a given temperature range of 18 °C, the samples grown at different cooling rates appear different cross section views. Fig. 2a presents a schematic diagram for the sample of 0.3 °C/h, which displays a unitary c-axis orientation and the c-axis is vertical to the surface of sample. For the samples grown at the cooling rate above 0.5 °C/h, the unitary c-axis oriented region reduces with the cooling rate increasing. For example, the region does not reach the bottom for the sample at a cooling rate of 1.0 °C/h as shown in Fig. 2b. The above-mentioned results mean that the slower cooling rate, the more beneficial for the single domain growth. In addition, the cooling rate being faster than the crystal growth rate could cause the imperfect single domain. As viewed from the single domain growth only, it is considered that the cooling rate of 0.2 or 0.3 °C/h is the best. Fig. 3 shows the relationship between the normalized DC magnetization and the temperature. It
3. Results and discussion Two photos of the top surface view for samples with 11 mm in diameter are shown in Fig. 1. It is obvious that the cooling rate affects the size of single domain. A perfect single domain sample was prepared at a cooling rate of 0.3 °C/h, as seen in Fig. 1a. The same top surface views were also obtained for the samples grown at different cooling rates of 0.2–1.1 °C/h. When the cooling rate was larger than 1.3 °C/h, a small single domain was
Fig. 2. Schematic diagrams of the cross section for samples prepared at different cooling rates of (a) 0.3 °C/h and (b) 1.1 °C/h.
264
L. Xiao et al. / Physica C 386 (2003) 262–265
30
0.0
Normalized M
-0.4 -0.6
Jcm (KA/cm2)
1.3 C/h O 1.1 C/h O 1.0 C/h 0.75OC/h O 0.5 C/h 0.3 OC/h
-0.2
1.3 OC/h 1.1 OC/h 1.0 OC/h 0.75OC/h 0.5 OC/h 0.3 OC/h
25
O
-0.8
20 15 10 5
-1.0
0 60
70
80
90
100
110
0.0
T (K)
can be seen in this figure, Tc;onset drops and DT becomes wide obviously with the cooling rate decreasing. As shown in Fig. 4, Tc;onset is almost changeless when the cooling rate is above 1.0 °C/h, and it decreases rapidly when the cooling rate is below 0.5 °C/h, especially for the sample of 0.2 °C/ h Tc;onset drops below 77 K. Fig. 5 shows the curves of the magnetization critical current density Jcm at 77 K versus applied magnetic field for the samples grown at different cooling rates. It is obviously that the Jcm characteristic is the best for the sample of 1.0 °C/h and it has the peak effect. Fig. 6 reveals the relationship between Jcm and the cooling rate, from which we can see the Jcm value is high at the cooling rate range from 0.9 to 1.3 °C/h. However, the Jcm de-
1.0
1.5
2.0
2.5
3.0
B (T) Fig. 5. Dependence of the magnetization critical current density Jcm on B for different cooling rate.
16
Jcm (kA/cm2)
Fig. 3. Dependence of normalized magnetization M on temperature T for different cooling rate.
0.5
Sample:Φ11 mm T : 77 K
12 8 4 0 0.3
0.6
0.9
1.2 O
Cooling rate ( C/h) Fig. 6. Dependence of the magnetization critical current density Jcm on cooling rate at 77 K.
95
Tc, onset
90 85 80
sample:Φ11 mm
75 70
0.2
0.4
0.6
0.8
1.0
1.2
O
Cooling rate ( C/h) Fig. 4. Dependence of Tc;onset on cooling rate.
1.4
creases obviously when the cooling rate is below 0.75 °C/h, it is about one order of magnitude lower for 0.5 °C/h than 1.0 °C/h. The result of the Jcm is in agreement with that of Tc . The measured result of levitation force provides further evidence that the influence of the cooling rate on the superconducting properties of the sample is very strong. As shown in Fig. 7, the maximum f0 value was obtained for the sample with 11 mm in diameter grown at the cooling rate of 1.0 °C/h. With increasing the sample size, the cooling rate corresponding to the maximum value of f0 shifts to the lower, which is about 0.3 °C/h for the sample with 30 mm in diameter.
L. Xiao et al. / Physica C 386 (2003) 262–265
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indicate that cooling rate has an optimum range, which is 0.9–1.1 °C/h for sample with 11 mm in diameter. It shifts to the lower with the sample size increasing, about 0.3 °C/h is suitable for the sample with 30 mm in diameter. The sample grown at this cooling rate not only has single domain structure and higher Tc , Jcm as well as the levitation force f0 but also shorten processing time greatly which is beneficial to reduce manufacturing expenses. Acknowledgements Fig. 7. Relationship between the cooling rate and the levitation force density at zero distance.
According to above-mentioned results, the cooling rates of 0.9–1.1 °C/h are suitable to obtain better single domain and higher Tc , Jc and f0 for the sample with 11 mm in diameter. For a given temperature range of 18 °C during the crystalgrowth, the cooling rates of 0.2 and 1.0 °C/h correspond to the time of 90 and 18 h, respectively. Therefore, the single domain sample grown at the cooling rate of about 1.0 °C/h not only shortened greatly processing time but also exhibited the higher superconducting properties compared with the others.
4. Conclusions The influences of the cooling rate on the single domain growth and the superconducting properties have been studied. The experimental results
This work was supported by the National Center for Research and Development of Superconductivity (Projects of 863 and 973). References [1] R. Tournier, E. Beaugnon, O. Belmont, X. Chaud, D. Bourgault, D. Lsfort, L. Porcar, P. Tixador, Supercond. Sci. Technol. 13 (2000) 886. [2] D. Lizkendorf, T. Habisreuther, M. Wu, T. Strasser, M. Zeisberger, W. Gawalek, M. Helbig, P. Gornert, Mater. Sci. Eng. B 53 (1998) 75. [3] M. Ullrich, H. Walter, A. Leenders, H.C. Freyhardt, Physica C 311 (1999) 86–92. [4] J.C.L. Chow, L. Wai, C.D. Dewhurst, H.-T. Leuug, D.A. Cardwell, Y.H. Shi, Supercond. Sci. Technol. 10 (1997) 435. [5] H.T. Ren, L. Xiao, Y.L. Jiao, S.A. Chang, X.H. Wang, Y.L. Wang, Physica C 282–287 (1997) 485. [6] L. Xiao, H.T. Ren, Y.L. Jiao, M.H. Zheng, Y.X. Chen, ISMAGLEV (2002) Chengdu of China, submitted for publication. [7] A. Umezawa, G.W. Crabtree, J.Z. Liu, H.W. Weber, W.K. Kwok, L.H. Nunez, T.J. Moran, C.H. Sowers, H. Claus, Phys. Rev. B 36 (1987) 7151.