Superconducting properties of bulk Bi 1.6Pb 0.4Sr 2Ca 2− x Cd x Cu 3O 10 system prepared via conventional solid state and coprecipitation methods

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  Superconducting properties of bulk Bi 1.6 Pb 0.4 Sr 2 Ca 2  x Cd x Cu 3 O 10 system prepared via conventional solid stateand coprecipitation methods I. Hamadneh  a,* , A. Agil  b , A.K. Yahya  c , S.A. Halim  b a Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia b Department of Physics, Faculty of Science, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia c Faculty of Applied Sciences, Universiti Teknologi MARA, Shah Alam, Selangor, Malaysia Accepted 20 March 2007Available online 24 May 2007 Abstract The effect of Cd doping on the superconducting properties of BSCCO system with nominal starting compositions of Bi 1.6 Pb 0.4 Sr 2 -Ca 2  x Cd x Cu 3 O 10  ( x  = 0.00–0.10) was studied. The preparation methods used to prepare the samples are the conventional solid-stateoxide powder (SSR) and the coprecipitation (COP) techniques. Resistivity versus temperature measurements ( R  –  T  ) showed that alldoped samples exhibited metallic behaviour. For the SSR samples, existence of a two step feature was observed at  x  = 0.07 indicatingthe presence a lower temperature 2212 phase together with the higher temperature 2223 phase. This behaviour resulted in the shifting of the  T  C( R =0)  towards lower temperature. However, the COP samples showed better superconducting properties probably due to higherhomogeneity resulted from mixing of sub-micron particles during sintering. The  R  –  T   curve did not display any two step features dueto the single phase nature of the samples. This is confirmed by the XRD data where Bi-2212 phase was minor. In addition, small amountof doping ( x  = 0.02 in COP and SSR samples) enhanced the phase formation and  T  C( R =0) .   2007 Elsevier B.V. All rights reserved. PACS:  74.62.  c; 74.62.Dh; 74.72.Hs Keywords:  Superconductor; Cd substitution; Phase formation 1. Introduction It is widely known that Bi(Pb)–Sr–Ca–Cu–O supercon-ductor can be produced by conventional solid-state route[1] or wet routes such as oxalic coprecipitation [2], sol–gel [3,4] and micro-emulsion-based techniques [5]. The wet route is been the focus of research to produce Bi(Pb)–Sr– Ca–Cu–O powders with high compositional homogeneity[6]. Further investigation on the effect of substitution inBSCCO system provides an opportunity to vary its func-tional and mechanical properties [7]. Elemental substitu-tion can influence the kinetics and mechanism of HTSCphase formation, thus changing the final microstructureof the superconductor [6]. In addition, the substitutioncan form fine inclusions of stable phases serving as effectivepinning centers [7]. This way seems to be attractive for fur-ther improvement of critical current density in Bi(Pb)-2223tapes [7,8].In this paper, comparisons were carried out on Cddoped Bi 1.6 Pb 0.4 Sr 2 Ca 2  x Cd x Cu 3 O 10  using COP and SSRprocesses. The substitution or doping of Cd at Ca site withnominal concentrations of   x  = 0, 0.02, 0.05, 0.07 and 0.10were used. Systematic investigations on the superconduc-ting properties were performed using DC electrical resis-tance–temperature measurements; XRD and SEM arereported. 0921-4534/$ - see front matter    2007 Elsevier B.V. All rights reserved.doi:10.1016/j.physc.2007.03.445 * Corresponding author. Tel.: +603 89467494; fax: +603 89432508. E-mail address: (I. Hamadneh). Physica C 463–465 (2007) 207–210  2. Experimental  2.1. Conventional solid-state route (SSR) SSR was used to prepare Bi 1.6 Pb 0.4 Sr 2 Ca 2  x Cd x Cu 3 O 10 ( x  = 0.00, 0.02, 0.05, 0.07 and 0.10) by mixing Bi 2 O 3 ,CaCO 3 , PbO, SrCO 3 , CdO and CuO (purity P 99.9%) inappropriate proportions. Heat treatments were 12 h of cal-cination at 800   C followed by pre sintering at 830   C for24 h was performed. The powders were then regroundand then pressed into pellets of    12.5-mm diameter and2 mm thickness before sintered at 850   C for 150 h fol-lowed by cooling at 120   C/h.  2.2. Coprecipitation method (COP) Bi 1.6 Pb 0.4 Sr 2 Ca 2  x Cd x Cu 3 O 10  samples ( x  = 0.00, 0.02,0.05, 0.07 and 0.10) were prepared via COP processdescribed in Ref. [9]. Grinding and heating steps for thecoprecipitated powders were repeated three times. The firstheating was at 730   C for 12 h in air to remove the remain-ing volatile materials. The second was at 845   C in air toensure the elimination of the 2201 phase. The powderwas then pressed into pellets and heated up to 850   C for24 h and cooled to room temperature at 120   C/h.Resistivity versus temperature measurements ( R  –  T  ) of all the samples were carried out using the four-point probetechnique with silver paint contacts. The samples were also Fig. 1. XRD analysis for the Bi 1.6 Pb 0.4 Sr 2 Ca 2  x Cd x Cu 3 O 10  prepared via(a) SSR method and (b) COP method. The 2223 and 2212 phases aremarked with ( § ) and (  ), respectively.Fig. 2. Volume % of the phase formation at various volume fraction of Cdsynthesized via COP and SSR. The solid line is just as a guide to the eye.Fig. 3. Electrical resistance (d.c.) as a function of temperature forBi 1.6 Pb 0.4 Sr 2 Ca 2  x Cd x Cu 3 O 10  samples synthesized via (a) SSR and (b)COP techniques.208  I. Hamadneh et al. / Physica C 463–465 (2007) 207–210  examined by X-ray powder diffraction with Cu K a  radia-tion using Phillips PW1830 diffractometer over the rangeof 4–60  . Microstructure of the samples was recorded usinga JEOL 6400 scanning electron microscope. 3. Results and discussion XRD patterns showed that the SSR samples with0 <  x  < 0.02 exhibited single phase with tetragonal struc-ture (Fig. 1a). Above that concentration a strong transitionfrom Bi-2223 phase to Bi-2212 phase observed. However,the COP samples showed a high dominancy of 2223 phasewith minor Bi-2212 phase for all samples (Fig. 1b). Thevolume fractions of high- T  C  and low- T  C  phases can be esti-mated from the intensities of high- T  C , low- T  C  phase peaksand other peaks observed, as used in Ref. [10], namely,Bi-2223  ð % Þ¼ P  I  2223 P  I  2223 þ P  I  2212 þ P  I  others  100 %  ð 1 Þ Bi-2212  ð % Þ¼ P  I  2212 P  I  2223 þ P  I  2212 þ P  I  others  100 %  ð 2 Þ where  I   is the peak intensity of the present phases. An in-crease in the high- T  C  phase for SSR and COP samples( x  = 0.02) was observed, where the proportions of Bi-2223/Bi-2212 (%) in the phase mixture were 92/8 and 98/2, respectively. Above the concentration ( x P 0.05) theBi-2223 phase decreased drastically for SSR sampleswhereas the high- T  C  phase for the COP samples remaineddominant (Fig. 2).The normalized resistance to room temperature of thesamples is presented in Fig. 3. All samples displayed metal-lic behaviour followed by a shift in  T  C( R =0)  towards lowertemperature with Cd content. Highest critical temperaturefor both SSR and COP series was observed at  x  = 0.02with  T  C( R =0)  value of 104 K. A two step feature wasobserved for SSR samples with  x  = 0.07 indicating thetotal dominancy of 2212 phase (Fig. 3).Since the ionic radius of Ca 2+ (1.12 A˚) is greater thanthat of Cd 2+ (0.97 A˚) [11], the Cd ions will causes a distor-tion between the slabs of the Bi-2223 system leading to theformation of Bi-2212 with  x P 0.02. This was moreobserved in the SSR samples where larger grain size of the starting powders and longer sintering time permittedCd 2+ to diffuse into the crystal structure. However, themixing at sub-micron level of the oxalate powdersenhanced the solid state reaction and shortens the sinteringtime to form the high- T  C  phase. Cd ions might be washedout to the grain boundaries to form weak links and leadingto a gradual decrease in the  T  C( R =0) .SEM micrographs for the Cd substituted samples dis-played layers of thin flaky plate-like grains randomly dis-tributed for the SSR samples (Fig. 4a). It is clearlyobserved that the grains started to degrade and to formsmaller plate-like grains which belong to 2212 phase atCd concentration  x P 0.05. However, COP samples(Fig. 4b) showed a certain degree of orientation at lower Fig. 4. SEM micrograph for Bi 1.6 Pb 0.4 Sr 2 Ca 2  x Cd x Cu 3 O 10  samples at  x  = 0.02 and  x  = 0.05 prepared via (a, c) SSR and (b, d) COP techniques. I. Hamadneh et al. / Physica C 463–465 (2007) 207–210  209  Cd concentration with a better compacted flaky plate-likestructure and less voids. 4. Conclusion In conclusion, Bi-2223:Cd system was prepared via SSRand COP methods with Cd doped at different concentra-tions ( x  = 0.02, 0.05, 0.07 and 0.10) at the Ca site. The sam-ples prepared via COP method exhibited better results withhigh dominancy of Bi-2223 phase as compared with SSRseries. An increase in the  T  C( R =0)  of 104 K and Bi-2223 %(98% and 92%) were observed for the sample with lowCd concentration of ( x  = 0.02) for COP and SSR samples,respectively. SSR samples showed that the 2223 phase isconverted to 2212 phase for concentrations  x  > 0.05, thisis due to the strong phase transition occurred at  x  = 0.05with consequent decrease in  T  C( R =0)  due to the formationof the weak links. However, applying the COP methodsenhanced the crystal growth of the high phase due to theformation of sub micron oxalate powders with an increasein the  T  C( R =0) . Thus, this material is a plausible candidatefor tapes production. Acknowledgements The financial support of the Ministry of Science, Tech-nology and Environment of Malaysia, under the IRPAvote: 4-07-05-026 is gratefully acknowledged. References [1] H. Maeda, Y. Tanaka, M. Fukutomi, T. Asano, Jpn. Appl. Phys.Lett. 27 (1988) L209.[2] Y.T. Huang, D.S. Shy, L.J. Chen, Physica C 294 (1998) 140.[3] C.Y. Shieh, Y. Huang, M.K. Wu, C.Y. Huang, Physica C 185–189(1991) 513.[4] S.A. Halim, S.A. Khawaldeh, H. Azhan, S.B. Mohamed, K. Khalid,J. Suradi, J. Mater. Sci. 35 (2000) 3043.[5] A. Tampieri, G. Celotti, S. Lesca, G. Bezzi, T.M.G. La Torretta, G.Magnani, J. Eur. Ceram. Soc. 20 (2000) 119.[6] C. Mao, L. Zhou, X. Sun, X. Wu, Physica C 281 (1997) 35.[7] P.E. Kazin, M.A. Uskova, Yu.D. Tertyakov, M. Jansen, S. Scheurell,E. Kemnitz, Physica C 301 (1998) 185.[8] M. Ishizuka, Y. Tanaka, H. Maeda, Physica C 252 (1995) 339.[9] I. Hamadneh, S.A. Halim, C.K. Lee, J. Mater. Sci. 41 (2006) 5526.[10] I.V. Driessche, A. Buekenhoudt, K. Konstantinov, E. Bruneel, S.Hoste, Appl. Supercond. 4 (1996) 185.[11] Z. Ozhanly´, M.E. Yakincy´, Y. Balcy´, M.A. Aksan, J. Supercond. 15(2002) 543.210  I. Hamadneh et al. / Physica C 463–465 (2007) 207–210
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