Advances in Condensed Matter Physics

Volume 2014 (2014), Article ID 498747, 8 pages

http://dx.doi.org/10.1155/2014/498747

Research Article

Transport Critical Current Density of (Bi1.6Pb0.4)Sr₂Ca₂Cu₃O₁₀ Ceramic Superconductor with Different Nanosized Co₃O₄ Addition

Nur Jannah Azman,¹ Huda Abdullah,² and Roslan Abd-Shukor¹

¹School of Applied Physics, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia

²Department of Electrical, Electronic and Systems Engineering, Faculty of Engineering and the Built Environment, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia

Received 19 December 2013; Accepted 7 January 2014; Published 19 February 2014

Academic Editor: Ram N. P. Choudhary

Copyright © 2014 Nur Jannah Azman et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

The effect of different nanosized Co₃O₄ (10, 30, and 50 nm) addition on the Bi1.6Pb0.4Sr₂Ca₂Cu₃O₁₀(Co₃O₄)x superconductor with  wt.% has been investigated using X-ray diffraction method, scanning electron microscopy, transition temperature, and critical current density measurements. The samples were prepared by the conventional solid-state reaction method. Samples with  wt.% Co₃O₄ (10 nm) showed the highest at 102 K. The highest was observed in the  wt.% Co₃O₄ (10 nm) and  wt.% Co₃O₄ (30 nm) samples. At 77 K, of the 10 nm and 30 nm Co₃O₄ added samples was 6 and 13 times larger than the nonadded samples, respectively. Small addition of Co₃O₄ nanoparticles in the Bi1.6Pb0.4Sr₂Ca₂Cu₃O₁₀ (Bi-2223) samples enhanced the critical current density and the phase formation. The larger Co₃O₄ nanoparticle (50 nm) had a greater degradation affect on superconductivity of the Bi-2223 phase.

1. Introduction

The critical current density, , is one of the most significant parameters for the successful application of high- superconductors. The pinning potential is one of the important factors that determine the critical current density. can be improved by introducing efficient pinning center with size that matches the coherence length, which can improve pinning potential and suppress the flux flow [1, 2].

Extensive researches have been done to improve the flux pinning properties of the Bi1.6Pb0.4Sr₂Ca₂Cu₃O₁₀ (Bi-2223) system [2–19]. Elemental substitution and addition of nanosized particles in high- superconductors are an easy and efficient method to improve the transport properties. Much effort has been done to improve intergrain links and the properties of the Bi-based superconductor, such as adding Al, Cr, Mg, Cd, Ag, Ni, Nb, Li, La, and Nd into high- superconductors [2–11].

The critical current density and transition temperature of Sm added samples were found to be higher than those of the pure samples with a maximum given by  wt.%, which is seven times higher than nonadded sample [12]. In Cr₂O₃ added Bi-2223 samples, the maximum and were observed for the sample with 0.5 wt.% [3]. In MgO added BiSr₂CaCu₂Oδ (Bi-2212) samples, the transition is narrow and the volume fraction increases with addition up to 9 wt.% [13]. The volume fraction of the Bi-2223 phase, lattice parameter, and zero-resistance temperature, , decrease with increasing MgCO₃ content [4]. The Fe₃O₄ magnetic nanoparticle and SiC have the ability to enhance the critical current density in Bi-2Sr₂Ca₂Cu₃O₁₀/Ag tape [14, 18].

Flux pinning can be optimized if the particle size is carefully controlled. With judicious addition level, these particles can improve flux pinning [7]. The pinning strengths of the flux lines can be enhanced by direct magnetic interaction of vortices with magnetic pinning centers.

The two important characteristic lengths in superconductors are the coherence length ξ and penetration depth . The critical current density is expected to increase if the pinning center is larger than but smaller than [20]. For Bi₂Sr₂Ca₂Cu₃O₁₀ system,  nm and  nm. For magnetic nanoparticles, a strong interaction between flux line network and the system can be expected if , where is the particle size [21]. The range between and is large and it is interesting to investigate the effect of different magnetic nanosized particles, that is, between 2.9 nm and 60 nm on (Bi,Pb-2223) superconductor.

Most studies on the nanosized particle addition into (Bi,Pb)-2223 have only been carried out with one average size. Preliminary results on the effect of Co₃O₄ on the formation of the Bi-2223 phase have been reported [22]. In this paper the effects of magnetic Co₃O₄ addition with average sizes 10, 30, and 50 nm in Bi1.6Pb0.4Sr₂Ca₂Cu₃O₁₀(Co₃O₄)x with were studied. These sizes are larger than but smaller than which satisfies the condition in [20]. This objective of this research was to determine the effect of different nanosized Co₃O₄ on the phase formation, structure, microstructure, and transport critical current properties of Bi-2223 superconductor.

2. Experimental Details

Superconducting powders precursor with nominal composition Bi1.6Pb0.4Sr₂Ca₂Cu₃O₁₀ were synthesized by using the coprecipitation method. The material was prepared using metal acetates of bismuth, lead, strontium, calcium and copper (purity ≥99.99%), oxalic acid, deionized water, and isopropanol. The dried-up powders were ground manually in agate mortar and calcined at 730°C for 12 h followed by an intermediate grinding before the second calcination at 845°C for 24 h. After cooling, the calcined powders were ground again and after that nanosized Co₃O₄ (US Research Nanomaterials Inc.) with average particle size of 10, 30, and 50 nm were added to the precursor powders with nominal composition Bi1.6Pb0.4Sr₂Ca₂Cu₃O₁₀(Co₃O₄)x with , 0.01, 0.02, 0.03, 0.04, and 0.05 wt.%. The samples were thoroughly mixed, ground, pressed into pellet of 2 mm thickness and 12.5 mm diameter, and sintered at 850°C for 48 h.

The electrical resistance-temperature measurements were carried out by the four-point probe technique in conjunction with a CTI cryogenics closed-cycle refrigerator (Model 22). The four-point probe method using the 1 μV/cm criterion was used to measure the transport critical current density between 30 K and 77 K.

The XRD diffraction patterns were recorded using a Bruker D8 Advance diffractometer with CuKα radiation. The microstructure of the samples was observed using a scanning electron microscope (SEM) Philips XL 30. The distribution of nano-Co₃O₄ in the sample and the presence of the different phases were analyzed by using a Philips energy dispersive X-ray analyzer (EDX) model PV99. The size of Co₃O₄ was determined using a Philips transmission electron microscope (TEM) model CM12.

3. Results and Discussion

TEM micrograph of the Co₃O₄ nanoparticles with average size around 30 nm is shown in Figure 1. Figures 2, 3, and 4 show the XRD patterns of the sample added with 10, 30, and 50 nm Co₃O₄, respectively. The samples consist of a mixture of Bi-2223 and Bi-2212 phase. H and L indicate the high- Bi-2223 phase and low- Bi-2212 phase, respectively. The volume fraction of the phases for all the samples is given in Table 1. Samples with  wt.% (10 nm),  wt.% (30 nm), and  wt.% (50 nm) showed the highest percentage of Bi-2223 phase, that is, 72, 74, and 72%, respectively. Further increase of Co₃O₄ decreased the percentage of the Bi-2223 phase and increased the percentage of the Bi-2212. The intensity of the peaks corresponding to the Bi-2223 phase decreases and the intensities of peaks corresponding to the Bi-2212 phase increase with further increase in Co₃O₄. The lattice parameters for the samples were  Å and  Å. A slight increase in the lattice parameter with almost no change in the and parameters was observed in the nano-Co₃O₄ added samples. The Co₃O₄ reflections were not observed in the XRD patterns due to the fact that the values are too small to be detected. Addition of 10 and 30 nm Co₃O₄ from to 0.04 wt.% increased the Bi-2223 phase volume fraction.

Table 1: Zero-resistance temperature (), volume fraction, critical current density () at 30 K, and 77 K in self-field.

(wt.%)
Volume fraction 

at 30 K
at 77 K

Bi-2223 (%)
Bi-2212 (%)
(±1 K)
(mA/cm²)
(mA/cm²)

(10 nm)

    0
51
49
100
371
26

    0.01
61
39
102
412
108

    0.02
61
39
101
590
122

    0.03
72
28
97
1232
358

    0.04
63
37
99
725
342

    0.05
51
49
95
986
82

(30 nm)

    0
51
49
100
371
26

    0.01
71
29
97
411
40

    0.02
74
26
95
1742
878

    0.03
67
33
91
1145
854

    0.04
53
47
98
1025
731

    0.05
47
53
94
440
236

(50 nm)

    0
51
49
100
371
26

    0.01
72
28
97
1389
923

    0.02
44
56
97
1018
609

    0.03
48
52
96
1262
508

    0.04
37
63
95
755
250

    0.05
37
63
93
428
170

Figure 1: TEM micrograph of Co₃O₄ with average grain size of 30 nm.

Figure 2: XRD patterns of the nonadded and 10 nm Co₃O₄ added Bi-2223 samples. (H) denotes the high- phase (Bi-2223) and (L) denotes the low- phase (Bi-2212).

Figure 3: XRD patterns of 30 nm Co₃O₄ added Bi-2223 samples. (H) denotes the high- phase (Bi-2223) and (L) denotes the low- phase (Bi-2212).

Figure 4: XRD patterns of 50 nm Co₃O₄ added Bi-2223 samples. (H) denotes the high- phase (Bi-2223) and (L) denotes the low- phase (Bi-2212).

Figure 5 shows the electrical resistance as a function of temperature between 60 and 200 K for all the samples. The dc electrical resistance measurements show metallic behavior in the normal state and a well-defined superconducting transitions for all samples. All the samples show the zero electrical resistance within the range of 91 to 102 K (Table 1), while onset temperature is between 83 and 115 K. The nonadded sample showed at 100 K. Samples with  wt.% Co₃O₄ (10 nm) showed the highest at 102 K. The high for the  wt.% sample may be due to homogeneity in the sample. Excessive Co₃O₄ degraded the superconductivity of Bi-2223, which can affect the transport properties in this type of material. The lower with increasing Co₃O₄ content also could be interpreted as a result of the suppression of superconductivity by Co₃O₄ [3].

(a)

(b)

(c)

Figure 5: Electrical resistance versus temperature curve for (a) nonadded sample and 10 nm Co₃O₄ added samples, (b) 30 nm Co₃O₄ added samples, and (c) 50 nm Co₃O₄ added samples.

Figure 6 shows the values at various temperatures for the 10, 30, and 50 nm Co₃O₄ added samples. The magnitude of in these samples is similar to those reported in the Y-based [23] and Bi-based [24] polycrystalline superconductors. It is clear that the addition of a small amount of Co₃O₄ enhanced the current-carrying capacity of the Bi-2223 ceramics. For the undoped sample, the at 77 K is about 26 mA/cm². The highest value of was observed in the  wt.% Co₃O₄ (10 nm) sample and  wt.% Co₃O₄ (30 nm) sample. At 77 K, of the 10 nm and 30 nm Co₃O₄ added samples was 6 and 13 times larger than the nonadded samples, respectively. However, the addition of Co₃O₄ (50 nm) decreased the at 77 K (0.01–0.05 wt.%) compared to the nonadded sample. The of the sample increased to 358 (mA/cm²) in the 0.03 wt.% Co₃O₄ (30 nm) sample at 77 K. The results, showed that nano-Co₃O₄ (30 nm) with  wt.% is the optimum amount for the highest . The added Co₃O₄ nanoparticles towards enhancing the critical current density for low concentration and for higher concentration it acts to suppress . The enhancing contribution is due to their magnetic and core vortex pinning forces. The suppressing contribution is due to their effect on the grain size and shape [7].

(a)

(b)

(c)

Figure 6: The critical current density as function of temperature for (a) 10 nm, (b) 30 nm, and (c) 50 nm Co₃O₄ added Bi-2223 samples.

Figure 7 shows the scanning electron micrograph of  wt.% (10 nm),  wt.% (30 nm), and 0.01 wt.% (50 nm) samples. For the nonadded sample, clean and flaky grains are observed which is the typical structure of the Bi-2223 system. The grain morphology of all the added samples is more or less identical except for minor variations in texture and porosity. The undoped sample showed the largest grain size. XRD analysis indicated that all samples with nano-Co₃O₄ showed the Bi-2212 peaks, which correspond to the low phase. However, the micrograph of  wt.% of Co₃O₄ (50 nm) showed a different surface morphology compared to nonadded sample. The microstructures reveal a minor difference in the porosity levels with lower levels of Co₃O₄. Thus, the addition of Co₃O₄ enhanced the sample morphology slightly. Thus, the Co₃O₄ nanoparticles have a clear effect on the microstructure of the sample. The decrease of the porosity level enhanced the critical current density [7]. The distribution Co₃O₄ in the samples with (10 nm), (30 nm), and (50 nm) is shown as white dots. The nanoparticles were dispersed on the surface of the grains and filled the weak links between the grains. For sample with (50 nm), there are many voids and pores. Moreover, the grain texture of this sample is also reduced compared to other samples.

(a)

(b)

(c)

(d)

Figure 7: SEM micrographs of (a) non-Co₃O₄ added sample, (b) added with 10 nm Co₃O₄ ( wt.%), (c) added with 30 nm Co₃O₄ ( wt.%), and (d) added with 50 nm Co₃O₄ ( wt.%). White dots are Co₃O₄.

In conclusion, the effect of nano-Co₃O₄ addition on flux pinning capability of bulk superconductor (Bi1.6Pb0.4)Sr₂Ca₂Cu₃O₁₀ was investigated. The larger Co₃O₄ nanoparticle (50 nm) had a greater degradation effect on superconductivity of the Bi-based materials. The highest was observed in sample with  wt.% Co₃O₄ (30 nm). Our results showed that suppression factors of the critical current density may dominate the enhancing factors for higher Co₃O₄ concentrations. With judicious amounts of Co₃O₄ nanoparticle of size 10 or 30 nm, the critical current density can be improved in the Bi-2223 superconductor.

Conflict of Interests

The authors declare that there is no conflict of interests regarding the publication of this paper.

Acknowledgments

This research has been supported by the Ministry of Education of Malaysia under Grant no. FRGS/2/2013/SG02/UKM/01/1 and Universiti Kebangsaan Malaysia under Grant nos. DLP-2011-018 and DIP-2012-032.

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