Nondestructive interactions of carbon nanotubes with Bi2Sr2CaCu2O8

Physica C 403 (2004) 145–150 www.elsevier.com/locate/physc

Nondestructive interactions of carbon nanotubes with Bi2Sr2CaCu2O8 D.H. Galvan a

a,*,1

, Shi Li a, W.M. Yuhasz a, J.H. Kim b, M.B. Maple a, E. Adem

c

Department of Physics and Institute of Pure and Applied Physical Sciences, University of California, San Diego, CA 92093, La Jolla, USA b Basic Research Laboratory, Electronics and Telecommunications Research Institute, Gajeong-dong 161, Yuseong, Daejon 305-350, South Korea c Instituto de Fısica-UNAM, Apartado Postal 20-364, CP 01000 Mexico, DF, Mexico Received 20 November 2003; received in revised form 12 December 2003; accepted 12 December 2003

Abstract Experimental evidence is presented for the intercalation of carbon nanotubes (CNs) in polycrystalline Bi2 Sr2 CaCu2 O8 (BSCCO) samples at the 12 wt.%-CN doping level, based on high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction measurements. Magnetization measurements performed on BSCCO samples with various CN doping levels do not indicate a change in the critical current density Jc within experimental error. The embedding process did not have any detrimental effects on the superconducting critical temperature of any of the samples. In contrast to previous work, the temperatures and widths of the superconducting transition of all the samples were similar.
2003 Elsevier B.V. All rights reserved. PACS: 74.72.)h Keywords: Superconductivity; Wetting; Nanotubes

1. Introduction Since the discovery of high temperature superconductivity (HTSC) in the cuprates [1–4] such as YBa2 Cu3 O7
x (YBCO) and Bi2 Sr2 CaCu2 O8 (BSCCO), a great deal of research has been carried * Corresponding author. Present address: Centro de Ciencias de la Materia Condensada-UNAM, Chemical Physics Department. Km. 107, Carretera Tij.-Ensenada, 22800 Ensenada BC, Mexico. Tel.: +52-646-174-4602; fax: +52-646-174-4603. E-mail address: [email protected] (D.H. Galvan). 1 On sabbatical leave from Centro de la Materia Condensada-UNAM, Apartado Postal 2681, CP, 22800 Ensenada BC, Mexico.

out on flux pinning in these materials in an effort to devise ways of increasing their critical current density Jc for technological applications. Various methods for enhancing the critical current density Jc in HTSC materials have been explored. For example, silver has been mixed with YBCO to produce YBCO/Ag tapes with superconducting properties improved over those of pure YBCO [5]. Silver can also be added as a dopant [6], or as a dispersed phase [7], or as a sheath in BSCCO/Ag composite wires [8]. Other methods such as the introduction of inclusions of the Y2 Ba2 CuOx (211 phase) into YBa2 Cu3 O7
x [9], and the exposure of HTSC samples to various types of high energy radiation have

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2003 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2003.12.010

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also been successful in increasing Jc . Gerhauser et al. [10] irradiated BSCCO (2212) single crystals with 0.5 GeV iodine ions to produce a well-defined columnar damage structure that served as flux pinning centers and resulted in a marked enhancement of Jc . More recently, Rangel et al. [11] succeeded in increasing Jc in polycrystalline YBCO/Ag thick films by subjecting the samples to electron irradiation at a dose of 1000 kGy. In this paper, we report on our efforts to explore the possibility of using carbon nanotubes to increase the critical current density of BSCCO. It has previously been shown by Fossheim et al. [16] and Huang et al. [17] that it is possible to embed nanotubes inside a BSCCO matrix with a subsequent enhancement in the inter-grain critical current density, due to the fact that carbon nanotubes have a shape and size similar to that of columnar defects induced in BSCCO by irradiation. However, these authors encountered a secondary detrimental effect in the superconductor that is due to the reaction between carbon and oxygen that complicated the interpretation of their results. In previous studies [12], we developed a method of embedding carbon nanotubes (CNs) in BSCCO (2212) samples. Unfortunately, wetting of the CNs by the BSCCO matrix is a necessary condition for enhanced flux pinning that is not a trivial matter to achieve. In this paper, we study the interaction of the carbon nanotubes with BSCCO-2212 due to our embedding technique as well as the effect of varying the doping levels of carbon nanotubes from 6 to 20 wt.% in samples of BSCCO-2212. The relative degradation level of the BSCCO matrix due to reactions with CNs was determined through measurements of the superconducting transition of the various samples using DC magnetization. The effects of embedded CNs on the critical current density Jc of the samples were ascertained by means of DC magnetization measurements. The embedded carbon nanotubes were examined by HRTEM and X-ray diffraction analysis.

2. Experimental The Bi2 Sr2 CaCu2 O8 (BSCCO) samples were prepared by means of solid-state reaction tech-

niques [12]. Stoichiometric amounts of Bi2 O3 , SrCO3 , CaCO3 and CuO were mixed and ground in an agate mortar, and sintered several times at temperatures ranging from 650 to 900 C, with intermediate grindings. The BSCCO powder was then annealed at 650 C for 20 h, first in oxygen and then in argon. Carbon nanotubes were obtained by irradiating graphite (Alfa–Aesar 99.99%) in a 2 MV Van de Graaf accelerator (High Voltage Engineering Corp.). The irradiation conditions were: 1.3 MeV energy, 5 lA current, 25 kGy/min dose rate, and 1000 kGy total dosage. The dosimeter used was a radiochromic film (FWT-60) from Far West Technology. X-ray diffraction measurements were performed with a Philips XRD/XÕPERT system using Cu Ka radiation at a voltage of 40 KV and a current of 45 mA. To embed the carbon nanotubes into the BSCCO powder, carbon nanotubes (6, 12 and 20 wt.%) were added to 10 ml alcohol and sonicated for 2–3 min. The sonicated solution was allowed to stand until the graphite settled out of the carbon nanotube solution. Appropriate amounts of the carbon nanotube solution were added to each batch of BSCCO powder (0.5 g) by carefully pouring the liquid on top of the BSCCO powder. Great care was taken to avoid introducing graphite into the BSCCO samples since, according to our experience during the sample preparation, graphite is detrimental to superconductivity. In this way, four different samples with various carbon nanotube contents were prepared. The samples were dried on a furnace grating at 100 C until the alcohol evaporated completely. Small pellets were pressed from the BSCCO powders with different carbon nanotube concentrations. The pellets were annealed in flowing argon at 650 C for 20 h, and then annealed in flowing oxygen at the same temperature for 20 h. The main purpose of the argon annealing was to stop the deleterious reaction of any carbon with BSCCO, and the subsequent oxygen annealing was to make up for the oxygen lost during the argon annealing. For TEM studies, the CN embedded BSCCO samples were ground in an agate mortar and placed on carbon-coated copper grids. The microscope used was a JEOL JEM-2010 with a

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3. Results and discussion X-ray diffraction was performed in order to detect any possible changes within the unit cell due to the CNs in the BSCCO samples. The XRD patterns for pure BSCCO and CN-embedded BSCCO samples with different concentrations of CN are shown in Fig. 1. The XRD pattern of the 20 and 6 wt.%-CN samples match well with that of the pure BSCCO, while the XRD pattern of the 12 wt.%-CN sample appears different with a double peak near 2h  29 that is clearly observable. This difference may be caused by the carbon nanotubes that have become embedded in the BSCCO grains, which could result in an expansion of the lattice. Further measurements such as a Rietveld analysis would be necessary in order to confirm this finding. Since XRD analysis can not provide conclusive evidence of the wetting of carbon nanotubes, HRTEM was performed to determine whether the carbon nanotubes are, in fact, embedded in the BSCCO matrix, and to determine where they are located. HRTEM images taken on the CN-

BSCCO w/ carbon nanotubes 3

8 10

Intensity (arbitrary units)

point to point resolution better than 0.19 nm. The SEM analysis was performed using a JEOL JSM 5300 microscope. From the TEM analysis it was estimated that 40% of the CNs introduced into the samples were present after the final annealing. Thus, the actual CN concentration is about 40% of the nominal CN concentration. In order to be consistent with previous work, the CN concentration quoted for each sample is the nominal concentration. Rectangular bar-shaped samples of dimensions 5 · 3.3 · 1.7 mm were used in magnetization M measurements which were made in a commercial Quantum Design MPMS and MagLab2000 magnetometers. The superconducting transition temperature was determined from the MðT Þ curve, measured upon warming in a small external field after first cooling the sample in zero field. The critical current density Jc of the sample was calculated from the hysteresis in magnetization DM in the M versus H isotherms based on standard theoretical models.

147

20 wt.% - CN

3

6 10

12 wt.% - CN

3

4 10

6 wt.% - CN

3

2 10

0 wt.% - CN

0

0 10

10

20

30

40

50

60

70

2θ (degrees) Fig. 1. X-ray diffraction patterns for pure BSCCO and BSCCO samples with nanotube (CN) contents of 6, 12, and 20 wt.%CN.

embedded BSCCO samples are shown in Fig. 2a–c for CN contents of 6, 12, and 20 wt.%, respectively. For comparison, Fig. 2d and e show a pure HRTEM image of BSCCO and a carbon nanotube. In Fig. 2a and c, corresponding to 6 and 20 wt.%-CN, respectively, CNs were observed between the grains of the BSCCO matrix. On the other hand, Fig. 2b, which corresponds to 12 wt.%-CN, clearly shows that CNs are embedded in the BSCCO grains, or, to be more precise, are situated between the BSCCO planes. After close examination of other areas of the 12 wt.%-CN sample, we found that, in a few cases, the CNs are located in between the grainÕs. However, in most cases, the CNs are actually embedded in the BSCCO matrix, as shown in Fig. 2b. It is not clear why the 12 wt.%-CN specimen resulted in wetting, while neither the 6 wt.%-CN nor 20 wt.%-CN samples exhibited wetting. Magnetization M versus temperature T data for the pure and the CN-embedded BSCCO samples are shown in Fig. 3. The MðT Þ measurements were performed by first cooling the sample in zero field to 10 K, applying a magnetic field of 10 G, and taking data on warming up to 100 K. The MðT Þ curves shown in Fig. 3 were normalized to the value of the magnetization at the lowest

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BSCCO BSCCO + 6 wt.% - CN BSCCO + 12 wt.% - CN BSCCO + 20 wt.% - CN

M/M 0

H=10 Oe

20

40

60

80

100

120

T(K) Fig. 3. DC magnetic susceptibility v (arbitrary units) as a function of temperature for BSCCO and BSCCO with different nanotube contents showing that the transition temperature Tc is not changed by the addition of carbon nanotubes.

Fig. 2. (a) and (c): High-resolution TEM micrographs for BSCCO with 6 and 20 wt.%-CN which show carbon nanotubes emerging from the BSCCO matrix. (b): TEM micrographs for BSCCO with 12 wt.% carbon nanotubes which show that the nanotubes are located between BSCCO planes, demonstrating that wetting has taken place. (d): TEM micrograph of pure BSCCO with a spacing of 2.67 nm that can be associated with the [0 2 2] direction. (e): TEM micrograph of a multi-walled carbon nanotube with a spacing of 0.332 nm between each tube.

measurement temperature of 10 K, M0 . The curves were also shifted vertically with respect to each other for viewing clarity. For all of the samples, the onset of the superconducting transition temperature Tc is close to 85 K, and the T -dependence of M is similar in the measurement temperature range from 10 to 100 K. The relatively constant Tc and similar temperature dependence indicate that the CN-embedding process successfully avoided reactions between the BSCCO matrix and the CNs. Magnetization M versus magnetic field H isotherms at T ¼ 5 K for pure and CN-embedded BSCCO samples are shown in Fig. 4. The shape of the MðH Þ hysteresis loops are typical for granular HTSC samples. The critical current density Jc can be calculated from MðH Þ data based on the Bean critical state model [13,14] using the following equation for a rectangular parallelepiped [15]. JC ¼ 20DM=½b
b2 =3a

ð1Þ

where a and b are dimensions of the superconducting grains transverse to the direction of the magnetic field such that a > b. DM is the difference in magnetization between the increasing and decreasing field branches of the hysteresis loops as

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149

Fig. 4. DC magnetization MðH Þ hysteresis loops for pure BSCCO and BSCCO with different nanotube contents at T ¼ 5 K.

shown in Fig. 4. DM was converted from emu per gram of sample to emu per cm3 of BSCCO using the known wt.% of BSCCO in the sample and the theoretical density of BSCCO. The average grain size is determined from the scanning electron micrographs, for pure BSCCO, BSCCO plus 6, 12, and 20 wt.%-CN, respectively. The values for the average grain size and calculated critical current density Jc for samples with various CN content are summarized in Table 1. The Jc calculations indicated that there is no change in critical current density (within experimental error) with increasing CN concentration as shown in Fig. 5. The measurements done on various slices of the BSCCO sample with 12 wt.%-CNs (Fig. 5) also indicate that the 12 wt.%-CN sample is not homogenous and may not have an even distribution of CNs. The results shown in Fig. 5 imply that the CNs were not successfully intercalated into the BSCCO

Fig. 5. Critical current measurements made at several carbon nanotube concentrations.

matrix except for the 12 wt.%-CN concentration based on the HRTEM image shown in Fig. 2b.

Table 1 Superconducting critical temperature Tc , average grain size, average width of the hysteresis loop (at H ¼ 2 kOe), and average intergranular critical current density Jc for pure BSCCO and BSCCO with different concentrations of carbon nanotubes Material

Tc (K)

Grain size (lm) b  a

Average DM (emu/gm)

Average Jc (MA/cm2 )

Pure BSCCO BSCCO–6 wt.%-CN BSCCO–12 wt.%-CN BSCCO–20 wt.%-CN

@85 @85 @85 @85

3.8 · 3.3 5.1 · 3.3 6.2 · 3.3 6.2 · 3.3

9.14 ± 1.03 8.33 ± 1.14 7.42 ± 3.17 7.66 ± 0.25

5.07 ± 0.57 4.48 ± 0.61 4.06 ± 1.74 4.61 ± 0.15

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4. Summary We have investigated the introduction of carbon nanotubes into a BSCCO matrix as a possible method of increasing the superconducting critical current density. X-ray diffraction and HRTEM indicate possible wetting of the carbon nanotubes by BSCCO in the 12 wt.% sample. While magnetization measurements do not indicate a change in Jc with CN concentration within experimental error, with the possible exception of the 12 wt.% sample. These results suggest that in all but the 12% sample the CNs were not successfully embedded within the BSCCO grains, but rather in grain boundaries. This seems to imply that either the embedding process did not go to sufficiently high temperatures to intercalate the CNs in the BSCCO matrix or the CN concentration was too low in all the samples. The results from the 12 wt.% sample showed that it was not homogenous and there may have been a greater CN concentration in the slices that showed an increased Jc . Though we were unsuccessful in showing an increase in Jc we were able to demonstrate that CNs could be introduced in BSCCO with no detrimental effects to the superconducting critical temperature Tc .

Acknowledgements D. H. Galv an would like to thank Prof. M. Avalos for fruitful discussions, and I. Gradilla, F. Ruiz, G. Vilchis, E. Aparicio and M. S aenz for technical support. Research at CMC-UNAM was supported by Conacyt under grant no. 36533-E and DGAPA-UNAM. Research at UCSD was supported by the US Department of Energy under

grant no. DE-FG03-86ER45230 and the subagreement under US Department of Energy Cooperative agreement no. DE-FC04-01AL67097.

References [1] M.K. Wu, J.R. Ashburn, C.J. Torng, P.H. Hor, R.L. Meng, L. Gao, Z.J. Huang, Y.Q. Wang, C.W. Chu, Phys. Rev. Lett. 58 (1987) 908. [2] H. Maeda, Y. Tanaka, M. Fukutomi, T. Asano, Jpn. J. Appl. Phys. 27 (1988) L209. [3] Z.Z. Sheng, A.M. Hermann, Nature 332 (1988) 138. [4] S.N. Putilin, E.V. Antipov, O. Chmaissem, M. Marezio, Nature 362 (1993) 226. [5] N. Wu, H.H. Zern, Ch. Chen, Physica C 241 (1995) 198. [6] D. Behara, N.C. Meishra, K. Potnik, J. Supercond. 10 (1997) 27. [7] R.R. Rangel, D.H. Galvan, G.A. Hirata, E. Adem, F. Morales, M.B. Maple, Supercond. Sci. Technol. 12 (1999) 264. [8] S.X. Dou, R. Zeng, B. Ye, Y.C. Guo, Q.Y. Hu, J. Horvat, H.K. Liu, T. Beales, X.F. Yang, M. Apperly, Supercond. Sci. Technol. 11 (1998) 915. [9] S. Sengupta, D. Shi, J.S. Luo, A. Buzdin, V. Gorin, V.R. Todt, C. Varanasi, P.J. McGinn, J. Appl. Phys. 81 (1996) 7396. [10] W. Gerhauser, H.W. Neumuller, W. Schmidt, O. Eibl, G. Saemann-Ischenko, S. Klaumunzer, Phys. Rev. Lett. 68 (1992) 879. [11] R. Rangel, D.H. Galvan, E. Adem, F. Morales, A. LiceaClaverei, M.B. Maple, J. Supercond. 12 (1999) 641. [12] D.H. Galvan, J.H. Kim, M.B. Maple, G.A. Hirata, E. Adem, Physica C 341–348 (2000) 1269. [13] C.P. Bean, Phys. Rev. Lett. 8 (1962) 250. [14] C.P. Bean, Rev. Mod. Phys. 36 (1964) 31. [15] M. Terasawa, N. Takezawa, K. Fukushima, T. Mitamura, X. Fan, H. Tsubakino, T. Kohara, K. Ueda, Y. Awaya, T. Kambara, M. Matsuda, G. Tatara, Physica C 296 (1998) 57. [16] K. Fossheim, E.D. Tust, T.W. Ebbesen, M.M.J. Treacy, J. Schwartz, Physica C 248 (1995) 195. [17] S.L. Huang, M.R. Koblischka, K. Fossheim, T.W. Ebbesen, T.H. Johansen, Physica C 311 (1999) 172.