SUPERCONDUCTIVITY AND MICROSTRUCTURE OF. ADDITION MgO NANOPARTICLES.

Transcription

1 SUPERCONDUCTIVITY AND MICROSTRUCTURE OF Tl 0.9 Bi 0.1 Sr 1.95 Ta 0.05 Ca 0.9 Y 0.1 Cu 2 O 7 CERAMICS WITH ADDITION MgO NANOPARTICLES. Running head: Superconductivity and Microstructure of Tl 0.9 Bi 0.1 Sr 1.95 Ta 0.05 Ca 0.9 Y 0.1 Cu 2 O 7 Ceramics With Addition MgO Nanoparticles. 8 9 Zulzamri Salleh 1, M.Yuzri M.Yusop ,2 Universiti Kuala Lumpur Malaysian Institute of Marine Engineering Technology, Dataran Industri Teknologi Kejuruteraan Marin, Bandar Teknologi Maritim, Jalan Pantai Remis, Lumut, Perak Malaysia. Tel. Off.: zulzamri@mimet.unikl.edu.my Abstract In this research, we investigated the effects of nanometer-sized MgO (Magnesium Oxide) addition ( wt. %) on superconducting and bulk properties of Ta-doped TlSr1212 prepared by solid state synthesis from Tl 0.9 Bi 0.1 Sr 1.95 Ta 0.05 CaCu 2 O 7 starting composition. We found the addition of small amount of MgO improved the superconducting properties and transport critical current density of bulk TlSr

2 Tl 0.9 Bi 0.1 Sr 1.95 Ta 0.05 CaCu 2 O 7 with 0.10 wt. % MgO showed T c zero of 60 K and addition of 0.20 wt. % MgO increased the T c zero to 80 K. Transport critical current density (J c ) at 40 K for the sample with 0.20 wt. % MgO was more than double the J c for the sample MgO(0.10 wt.%). However, further addition of MgO ( wt. %) caused T c zero and J c to decrease. The results showed that appropriate amount nano-mgo addition effectively improves the superconductivity and microstructure properties of TlSr1212. XRD and SEM with EDX investigations are also presented and discussed Keywords:Superconductor,Tl 0.5 Pb 0.5 Sr 1.8 Yb 0.2 CaCu 2 O 7,MgO nanoparticles Introduction The innovation on high-temperature superconductors (HTS) with critical temperature (T c ) generally above 77 K, which is the boiling point of liquid nitrogen, has opened the way for a much wider practical application of the materials. However, there are a number of limitations of cooper(cu) oxide superconductors, which must be overcome, amongst which are effect the performance of superconductivity such as weak magnetic flux pinning capability and poor mechanical properties, which may hinder effort for its full technological utilization. One way to increase the flux pinning ability is to introduce a suitable secondary phase by precipitation of the pinning phase 2

3 during processing as with production of Y 2 BaCuO 5 (Y211) precipitates during processing of YBa 2 Cu 3 O 7-δ (Y123) by Fossheim, Karkut, Heill, Slaski, Sagbahl, Vinokur, Murekami, Fujimoto, Koshizuka, Tanaka, Gencer, Abell and Gough, et al.(1992). Alternatively, foreign particles can be added directly into the superconductor matrix to provide extra flux pinning centers as achieved for Y-123 by Jin, Tiefel, Nakahara, Graebner, O Bryan, 53 Fastnacht and Lammlott, et al.(1990), Bi-2212 by Umemura, Egawa, Kinouchi, Tanimura, Nozaki and Utsunomiya, et al.(1992) and Bi-2223 by Dou, Liu and Guo, et al.(1992). It was reported that submicrometer sized Y-211 particles and nanometer-sized Ca 2 PbO 4 particles do have favorable effects on the flux pinning of melt-textured Y-123 and Bi-2223 bulk samples, respectively by Fossheim, Karkut, Heill, Slaski, Sagbahl, Vinokur, Murekami, Fujimoto, Koshizuka, Tanaka, Gencer, Abell and Gough, et al.(1992) and Anming, Xiaojun, Daoxiang, Zongquan, Jianyi, Yuping, Fapei and Jiaju, et al.(1994). MgO particles have been added in Bi-2212/Ag tapes by Huang, Hughus, Zheng and Jenkins et al.(1996), Bi-2212 bulk materials Wei, Schwartz, Goretta, Balachandran and Bhargava, et al.(1998) and YBCO bulk materials, which significantly enhance the critical current density (J c ) of these materials. Chen, Fang, Jiao, Zhang, Wen and Zhao et al. (1997) introduced nano-mgo particles into Y-123 and observed strongly enhanced flux pinning. Nanorods of MgO (20 to 30 nm) were incorporated into Bi-2212 thick film by Yang and Lieber et al. (1996) and resulted in a dramatically enhanced J c. Nanometer-sized MgO powders (10 20 nm) were 3

4 added into (Bi,Pb)-2223/Ag tapes and significantly enhanced the flux pinning of the material Zhao, Wan, Song, Sun and Du, et al. (2000). However, compared to other high-temperature superconductors, report on nano-mgo addition on Tl-based superconductors is very limited. In this paper, we report the influence of nanosize MgO on 1212 phase formation, microstructure, and transport critical current density (J c ) of bulk Tl 0.9 Bi 0.1 Sr 1.95 Ta 0.05 CaCu 2 O 7 samples Materials and Methods The samples were prepared by the two-step solid state reaction and precursor method from high purity (>99.99%) SrCO 3, Ta 2 O 5, CaO, and CuO powders. The precursor powders were mixed according to the Sr 1.95 Ta 0.05 Ca 09 Y 0.1 Cu 2 O 7 composition and ground using an agate mortar and pestle. The precursor powders were then calcined at around 900 C for 48 hours with several intermittent grindings. Appropriate amounts of Tl 2 O 3 and Bi 2 O 3 were then mixed with the precursor to form mixtures with nominal composition of Tl 0.9 Bi 0.1 Sr 1.95 Ta 0.05 CaCu 2 O 7. The mixtures were then pressed into pellets with diameter of 13 mm and thickness of around 2 mm under a load of 4-5 tons using a hydraulic press. The pellets were then placed in a ceramic boat and heated at around 1000 C for 5 to 6 minutes in flowing O 2 followed by furnace cooling to room temperature. Then the superconducting Tl 0.9 Bi 0.1 Sr 1.95 Ta 0.05 CaCu 2 O 7 powder was mixed with 0 to 0.8 wt. % nano-sized MgO (99 % purity) 4

5 having average microsize of 20 nm. After sufficient grinding, the powder was repressed into pellets and sintered in flowing O 2 in a tube furnace for 5-7 minutes before furnace cooled to room temperature. X-ray diffraction (XRD) analyses were performed using Bruker Model D8 Advance diffractometer with Cu-K α source. The volume fractions can be estimated by assuming that the amounts of 1212 and 1201 phases are proportional to the strongest diffraction line of each phase i.e. (103) reflection of 1212 phase and (102) reflection of 1201 phase. Electrical resistance measurements between 16 K and 300 K were measured using the standard four-point-probe method. A CTI Cryogenics Closed Cycle Refrigerator Model 22 and Lake Shore Temperature Controller Model 340 were used for temperature-dependent measurements. The temperature was recorded using a TG-120P GaAlAs diode sensor. Microstructure of internal sections of the samples was studied using JOEL model 6560 LA SEM Scanning Electron Microscope (SEM). The micro distribution with addition of nanoparticles MgO also has been investigated by using the Energy Dispersive X-Ray (EDX) machine attachment with SEM same model machine. The current densities J C were measured by the standard DC four-point probe technique using a criterion of 1µV/cm

6 116 Results and Discussion 117 Powder X-Ray Diffraction Analyses The Powder X-ray diffraction patterns for Tl 0.9 Bi 0.1 Sr 1.95 Ta 0.05 CaCu 2 O 7 with addition of nano-mgo (x = wt. %) showed all samples consist of dominant 1212 phase with tetragonal unit cell (space group P4/mmm) and 1201 minor phase. Figure 1(a) and Figure 1(b) shows X-ray diffraction patterns for Tl 0.9 Bi 0.1 Sr 1.95 Ta 0.05 CaCu 2 O 7 (x = 0.10 wt.% & 0.20 wt.%). The volume fraction of 1212 phase was found to decrease from 83 vol. % (x= 0.10 wt. %) to 76 vol. % (x =0.20 wt. %) (Table 1).The calculated lattice parameters of the 1212 phase did not show any systematic change of both a- and c-lattice with MgO content (Table 1). This indicates that the added MgO did not enter the Tl1212 structure during sintering. This section should contain Results and interpretation of the results in relation to existing knowledge Superconductivity of Critical Temperature, T c Normalized resistance versus temperature curve of Tl 0.9 Bi 0.1 Sr 1.95 Ta 0.05 CaCu 2 O 7 with x wt. % MgO (x = 0.10 wt.% and 0.20 wt.%) are shown in Figure 2. Addition of MgO (x=0.10 wt.%) into Tl 0.9 Bi 0.1 Sr 1.95 Ta 0.05 CaCu 2 O 7 also showed metallic normal state behavior and an increase in T c onset to 76 K and T c zero to 60 K. However, further addition 6

7 of MgO caused T c zero to increase from 60 K (x = 0.10 wt %) to 80 K (x = 0.20 wt%). The resistivity at 300 K shows a sudden increased from 8x10-3 Ω.cm (x = 0.10 wt. %) to 1.5x10-3 Ω.cm with addition of x = 0.2 wt. % MgO. Further addition of MgO generally caused resistivity to decrease from (x = 0.40 wt %) to (x = 0.80 wt %). The initial decrease in resistivity (x = 0.1) is accompanied by an increase in 1212 volume % but experimental data (Table 1) did not show any trend between resistivity and 1212 volume % for the samples. As such, the decrease in resistivity may not be attributed to an increase in 1212 phase volume SEM Micrographs and EDX Analyses of Addition MgO Nanoparticles Microstructure investigations using SEM may be able to draw further insight into the matter. SEM micrograph of fractured sections of Tl 0.9 Bi 0.1 Sr 1.95 Ta 0.05 CaCu 2 O 7 sample (Figure 3(a)) showed irregular grains with average smaller grains size of 1-2 µm for MgO (x=0.10 wt.%). When substitution of MgO (x=0.20 wt. %) (Figure 3(b)) caused the grains to become larger with average grain size of 4-10 µm. The grain boundaries appear to be slightly fused probably due to partial melting during high temperature sintering

8 Further addition of MgO did not further reduce the average grains size of the samples (not shown). Because MgO has a higher melting temperature compared to Tl1212 it is possible that the morphological differences between the small amount MgO and the more MgO added samples are related to increase of partial melting temperature of the composite as a result of MgO substitution. Although the actual average size of MgO in the sintered composite is not known due to the limited resolution of the SEM technique, we believe it is dispersed and resides between TlSr1212 grain boundaries, filling up pores and improving contact between grains causing the increase in resistivity as observed in Table 1. Based on energy dispersive x-ray (EDX) mapping result, it can be seen that the distribution of Mg element was homogenously dispersed for sample MgO 0.10 wt.% and 0.20 wt.%. Figure 4 and Figure 5 shows the EDX result with their chemical composition elements peak counts for MgO 0.10 wt.% and 0.20 wt.%. Observation from the EDX scanning result shows that Mg particle is only at single location if compared with others element. The elementary mass percentage (%) with difference MgO contents shows at Table 2. From the observation overall samples showed that when increase MgO nano particle the remaining Mg for each sample is increasing due to allocation of Mg is beside of Tl matrix planar. Only at MgO (0.20 wt.%) the mass is sudden decrease from to 0.23 % might be due to transition on partial melting condition and dissolve in planar defects

9 181 Critical Current Density, J c with Addition of MgO Nanoparticles Table 3 shows the variation of transport critical current density (J c ) at 20 K, 30 K, 40 K and 50 K with MgO content for Tl 0.9 Bi 0.1 Sr 1.95 Ta 0.05 CaCu 2 O 7. J c for all temperatures was consistently observed to increase to maximum value at x = 0.20 wt. % MgO before a sudden reduction at x=0.10 wt. %. For x=0.2 wt %, the J c slowly decreases between 20 K to 30 K and its reduce almost to half values with increasing MgO content. This phenomenon showed that decreasing in J c with increasing temperature can be explained as due to thermally activated flux creep by Matsushita, Fujiyoshi, Toko and Yamafuji, et al.(1990) which causes a relaxation of persistent current and reduces J c. The changes in J c for the MgO added samples might not be due to differences in microstructure of the samples between 0.10wt.% and 0.2 wt.% as SEM investigations while decreased MgO contents showed almost similar microstructure for all MgO added samples. As such, it is suggested that the changes are related to the enhanced flux pinning due to the introduction of 0.2 wt. % MgO at 20 K ~ 50 K. It must be acknowledged however, that the original sizes of MgO particles ( 20 nm) are much larger than the coherence length of the cooper pair in high-temperature superconductors (2-30 Å). In line with previous idea for Bi-2223 by Wan, Sun, Song, Wang, Jiang and Du, et al.(1998), if the average size of MgO in the composite is maintained in the sintered composite, the MgO particles may not be able to serve as pinning centers themselves. As such, the enhanced flux pinning with the addition of nano- 9

10 MgO particles may originate from the planar defects that are generated between the MgO particles and the TlSr1212 matrix Conclusions From this research we have been investigated the effects of nano-mgo addition ( wt. %) on superconducting and bulk properties of Ta-doped TlSr1212. We found that addition of a small amount of MgO (0.20 wt. %) improves the superconducting properties and transport critical current density, J c of TlSr1212. XRD investigations showed that the introduction of small amount of nano-mgo particles enhanced the 1212 phase formation process. The morphology of samples was observed by using SEM machine showed that grain size much bigger and gives the better connectivity among matrix plane. The EDX mapping showed that the distribution of Mg compound are fully distributed among the samples MgO 0.10 wt.% and 0.20 wt.%. The increase of the transport critical current density J c with 0.1 wt. % MgO, suggests enhancement of flux pinning ability due the nano-mgo addition. The behavior of J c in external magnetic field indicates presence of weak links at lower fields (< 0.1 Tesla) and strong percolation links at higher fields (> 0.1 Tesla). Addition of MgO nano particles, y = 0.20 wt.% for Tl 0.9 Bi 0.1 Sr 1.95 Ta 0.05 Ca 0.9 Y 0.1 Cu 2 O 7 produced faster decoupling of weak links at low fields. The addition of MgO resulted in the improvement of magnetic flux pinning, thus enhances the J c behavior for Tl1212 samples. 10

11 226 Acknowledgments I would like to give special thank to Universiti Kuala Lumpur, Malaysian Institute of Marine Engineering Technology for support the conferences grant References B. Zhao, X. Wan, W. Song, Y. Sun and J. Du, (2000) Nano-MgO particle 233 addition in silver-sheathed (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O x tapes, Physica C, : H. Anming, Z. Xiaojun, P. Daoxiang, L. Zongquan, J. Jianyi, S. Yuping, Z. Fapei and D. Jiaju, (1994) Chinese Science Bulletin, 39:601. K. Fossheim, M.G. Karkut, L.K. Heill, M. Slaski, L.T.Sagbahl, V.M. Vinokur, M. Murekami, H. Fujimoto, N.Koshizuka, S. Tanaka, F. Gencer, J.S. Abell and C.E. Gough, (1992). Flux dynamics and irreversibility in YBa 2 Cu 3 O 7 with Y 2 BaCuO 5 inclusions and in single crystal YBa 2 Cu 3 O 7,Phys. Scripta T,42: P.D. Yang and C.M. Lieber, (1996). Nanorod-superconductor composites: a pathway to materials with high critical current density Science Letter, 273(27):

12 Q.H. Chen, M.H. Fang, Z.K. Jiao, Q.R. Zhang, H.H. Wen and Z.X. Zhao, (1997) MgO nano-particles on flux pinning in YBa 2 Cu 3 O y system Science Bulletin, 42(5): S. Jin, T.H. Tiefel, S. Nakahara, J.E. Graebner, H.M. O Bryan, R.A. Fastnacht and G.W. Lammlott, (1990). Enhanced flux pinning by phase decomposition in Y-Ba-Cu-O. Apply Physics Letter, 56(13): S.L. Huang, D.D. Hughes, D.N. Zheng and R. Jenkins, (1996). Effects of MgO addition on phase evolution and flux pinning of Bi-2212/Ag tapes fabricated by electrophoretic deposition and partial-melting processing, Superconductor Science Technology, 9(5): S.X. Dou, H.K. Liu and Y.C. Guo, (1992). Improvement of flux pinning in the Ag clad Bi Pb Sr Ca Cu O wires through the use of a Apply Physics Letter, 60: T. Matsushita, T. Fujiyoshi, K. Toko and K. Yamafuji, (1990). Flux creep and irreversibility line in high temperature. Apply Physics Letter, 56: T. Umemura, K. Egawa, S.I. Kinouchi, J. Tanimura, A.Nozaki and S. Utsunomiya, (1992) J. Apply Physics Letter, 71:

13 W. Wei, J. Schwartz, K.C. Goretta, U. Balachandran and A. Bhargava, (1998). Effects of nanosize MgO additions to bulk Bi 2.1 Sr 1.7 CaCu 2 O x Physica C, 298(4): X. Wan, Y. Sun, W. Song, K. Wang, L. Jiang and J. Du, (1998) Physica C, 307: Table 1. T c onset, T c zero, room-temperature resistivity at 300K and 1212:1201 phase ratio and lattice parameters Tl 0.9 Bi 0.1 Sr 1.95 Ta 0.05 CaCu 2 O 7 with amounts of (0.10 wt.%) and (0.20 wt.%) MgO particles. Sample MgO (wt.%) T c onset (K) T c zero (K) Resistivity at 300K (x 10-3 Ω.cm) 1212:1201 Phase ratio (vol %) 1212 unit cell a (Å) c (Å) 13

14 0.10 wt.% : wt.% : Table 2. EDX scanning result for Mg and Tl mass(%) content. Element mass content (%) Sample MgO (wt.%) Mg

15 Tl Table 3. Show the critical current density (J c ) at 20 K, 30 K, 40 K and 50 K for Tl 0.9 Bi 0.1 Sr 1.95 Ta 0.05 CaCu 2 O 7. with addition MgO 0.10wt. % and 0.20 wt.%. Sample MgO (wt.%) Critical current density J c (A/cm 2 ) 20 K 30 K 40 K 50 K 15

16 0.10 wt.% wt.%

17 Intensity (a.u) * 110 * * θ (Degree) Figure 1 (a). Powder XRD patterns for Tl 0.9 Bi 0.1 Sr 1.95 Ta 0.05 CaCu 2 O 7 with amount of MgO 0.10 wt.% particles showing dominant 1212 phase. Peaks due to 1201 phase are indicating in parentheses (*). 17

18 Intensity (a.u) * * * θ (Degree) Figure 1 (b). Powder XRD patterns for Tl 0.9 Bi 0.1 Sr 1.95 Ta 0.05 CaCu 2 O 7 with amount of MgO 0.20 wt.% particles showing dominant 1212 phase. Peaks due to 1201 phase are indicating in parentheses (*)

19 Normalized Resistance (R(T) /R(300K)) Temperature (K) Figure 2 (a). Normalized resistance versus temperature curve Tl 0.9 Bi 0.1 Sr 1.95 Ta 0.05 CaCu 2 O 7 with MgO 0.10 wt.% show with difference T c zero and T c onset

20 Normalized Resistance (R(T) /R(300K)) Temperature (K) Figure 2 (b). Normalized resistance versus temperature curve Tl 0.9 Bi 0.1 Sr 1.95 Ta 0.05 CaCu 2 O 7 with MgO 0.20 wt.% show with difference T c zero and T c onset

21 Figure 3 (a). SEM micrographs MgO 0.10 wt.% show with difference grain size ze microstructure

22 Figure 3 (b). SEM micrographs MgO 0.20 wt.% show with difference grain size microstructure

23 Figure 4 (a). EDX mapping MgO 0.10 wt.% and show with difference micro distribution of Mg element

24 Figure 4 (b). EDX mapping MgO 0.20 wt.% and show with difference micro distribution of Mg element

25 Figure 5. Example EDX distribution elementary analysis output show the element per count for all chemicals composition for sample Tl 0.9 Bi 0.1 Sr 1.95 Ta 0.05 CaCu 2 O 7 with MgO 0.20 wt.%