2011) 2( 24مجلة ابن الهیثم للعلوم الصرفة والتطبیقیة المجلد للمركب الفائق التوصیل ةوالكهربائی ةتحضیر ودراسه الخصائص التركیبی Hg0.5Pb0.5-xSbxBa2Ca2Cu3O8+ δ كریم علي جاسم ، محمد عبد النبي ، مصطفى محمد علي ابن الهیثم، جامعة بغداد -قسم الفیزیاء، كلیة التربیة 2010، تشرین االول ،5: استلم البحث في 2011، شباط، 8: قبل البحث في الخالصة ــق ــــ ــات الزئبــ ــــ ـــرت مركبـ ــاص –حضــــ ــــ ــــ–الرصـ ـــــوني الفائقــــ ـــیل ذ ةاالنتیمــ ــیغ والتوصــــ ــــ -Hg0.5 Pb0.5 ةالصـ xSbxBa2Ca2Cu3O8+δ (x=0, 0.10 and 0.15) ة تفاعـل الحالـة الصـلبة باسـتعمال اسـتعملت .ثـالث خطـوات بطریقـ ـاد درجــة الحــرارة الحرجــة (point probe 4) ةالكهربائیــة تقنیــة المقاومیــ Hg0.5المركــب ةن عینــأووجــدنا Tcإلیجـ Pb0.5Ba2Ca2Cu3O8.437 المركـب ةا عینـمـسـلوك شـبه موصـل بین وذاHg0.5 Pb0.4Sb0.1Ba2Ca2Cu3O8.353 هـي ةدرجـ والتوصـیل ذ ةهـي فائقـ Hg0.5 Pb0.35Sb0.15Ba2Ca2Cu3O8.233المركـب ةسـلوك معـدني موصـل لكـن عینـ وذ وأظهـرت هـذه ةتراكیب معینیه قائم ون المركبات ذأبینت تحلیالت االشعة السینیة . 126Kتساوي (Tc(0ff)) ةانتقالی ةحرار االنتیموني تسبب ةنسب ةمقارنة مع الخالیة منه وان زیاد Sbاالنتیموني ةمع زیاده نسب cالتحلیالت نقصان في قیمة الثابت . c/aو ρM ةالكتلی ةونقصان في كال من الكثاف (Vphase(1223))الطور ةفي نسب ةزیاد ةالكتلی ةالكثاف، تحلیالت االشعة السینیة، درجة الحرارة الحرجة ، ةالكهربائی ةالمقاومی-:ةالكلمات المفتاحی IBN AL- HAITHAM J. FOR PURE & APPL. SCI. VOL.24 (2) 2011 Synthesis and Study Structural and Electrical Properties of Hg0.5Pb0.5-xSbxBa2Ca2Cu3O8+ δ Superconductors K. A. Jasim, M. Abdul-Nebi and M. M. Ali Department of Physics, College of Education Ibn-Al-Haitham, University of Baghdad Received in : 5, October , 2010 Accepted in : 8, February, 2011 Abstract Mercury-lead-antimony based superconductors with the formula Hg0.5 Pb0.5- xSbxBa2Ca2Cu3O8+δ (x=0, 0.10 and 0.15) have been prepared by useing three step solid state reaction processes. Electrical resistivity, using four probe technique, is used to find the transition temperature Tc. It is found from that sample Hg0.5 Pb0.5Ba2Ca2Cu3O8.437 is semiconductor , sample Hg0.5 Pb0.4Sb0.1Ba2Ca2Cu3O8.353 is normal state with metallic behaviors, while sample Hg0.5 Pb0.35Sb0.15Ba2Ca2Cu3O8.233 is superconducting state with critical transition temperature (Tc) is 126K. X-ray diffraction (XRD) analysis showed a tetragonal structure with decrease in the c-axis lattice constant for the samples doped with Sb as compared with these which have no Sb content. It was found that the increase of the Sb concentrations of all our samples produce an increase of the volume fraction (Vphase) and decrease c/a and Mass density ρM . Key words:- Electrical resistivity, Transition temperature, X-ray diffraction and Mass density Introduction Superconductivity in the Hg-based cuprate family having the generic formula HgBa2Can- 1CunO2n+2 ([Hg-12(n-1)n], Hg-Ba-Ca-Cu-O, HgBCCO) was first reported in 1993 [1] for the n = 1 compound (Hg-1201). Shortly thereafter, a record high TC of 133 K was reported for the n = 3 compound (Hg-1223) under ambient conditions [2]. Subsequently, it was found that TC values in excess of 164 K could be induced in the Hg-1223 by the application of a high pressure [3]. The Hg-1223 samples are known to degrade rapidly after synthesis. In view of this, significant efforts have recently been made to improve the stability of the Hg bearing HTSC phases, particularly the Hg-1223 phase. It is now known that the most effective way to improve the stability of the Hg-1223 phase is through suitable cationic substitution for Hg. Typically suited cations are those having oxidation states higher than that of Hg +2 greater than + 2 such as, Tl+3, Pb, Bi+3 , and Re[4-7] . They bring in more oxygen in the oxygen deficient HgO δ layer leading to phase stability. The higher oxidation state cations also lead to hole optimization in the hole deficient as grown Hg-1223 phase, thus producing optimum critical transition temperature (Tc). In the present work we have successfully prepared Hg0.5Pb0.5-xSbxBa2Ca2Cu3O8+δ bulk polycrystalline superconductor by using three step solid state reaction process, we have doped Hg0.5 Pb0.5Ba2Ca2Cu3O8+δ with Sb taken in varying concentrations stability of Hg(Pb)-1223 phase. Experimental The synthesis of Hg0.5 Pb0.5-xSbxBa2Ca2Cu3O8+δ HTSC phases (x= 0, 0.10 and 0.15) have prepared solid state reaction method , using appropriate weights of pure powders (99.998% IBN AL- HAITHAM J. FOR PURE & APPL. SCI. VOL.24 (2) 2011 from May & Baker LTD Dagenham England) materials of HgO, , Pb2O3, Sb2O3,BaCO3, CaCO3 and CuO. The weight of each reactant was measured by using a sensitive balance type (Mettler H35 AR with Capaci ty: 110 grams and Readabi lity: 0. 001).The synt hesis of the samples have been carried out by three step precursor method. In the first step, the powders (BaCO3, CaCO3 and CuO)were mixed together by using agate mortar ; a sufficient quantity of 2- propane was to homogenization the mixture and to form slurry during the process of grinding for about (30-50) minute.The mixture was dried by an oven at (200 0 C). The mixture was put in tube furnace that has programmable controller type [Eurptherm 818], for calcinations, which is the heat treatment to remove CO2 gas from the mixture. For this process the powder was heated to temperature of (800 0C) for three hours with a rate of (200 0C /hr) , then cooled to room temperature by the same rate of heating. In the second step, the Ba2Ca2Cu3O7 precursor was mixed with HgO, Sb2O3 and Pb2O3 to obtain the nominal compositions Hg0.5 Pb0.5-xSbxBa2Ca2Cu3O8+δ where x=0.0, 0.10 and 0.15. The powder was pressed into disc-shaped pellets (1.3 cm) in diameter and (0.2-0.3 cm) thick, using hydraulic press type (Specac) under a pressure of 8 ton/cm2 .The pellets were presintered in air at (855-860) 0 C for (8 hours) with a rate of (200 0 C/hr) and then cooled to room temperature by same rate of heating. In the third step, the pellets were reground, repressed and resintered in the oxygen (oxygen rate 0.6 L/min) at the same range of temperature for further (12 hours) and then cooled to (500 0C) and annealed in oxygen for (4 hours) and then cooled to room temperature by the same rate of heating. The samples were examined with resistivity experiments by using standard four-probe technique which is most common method of determining the Tc of a superconductor. The sample was fixed in the cryostat instrument which was joined to a rotary pump to get a pressure of 10-2 mbar inside the cryostat, and also joined to a sensor of digital thermometer (type Pt 100 resistance to temperature detection RTD) near the sample position . A 10 mA current was supplied to the sample by a current source D.C power supply type (Electronica- Veneta DV 30/V3); the voltage drop was measured by a Keithley model 180 nanovoltmeter with sensitivity of a bout  0.1 nanovolt was used for voltage measurements. The resistivity (ρ) could be found from the relation: ρ = L t I V  Where : I is the current passing through the sample, V is the voltage drop across the electrodes, ω is the width of the sample, L is the effective length between the electrodes, t is the thickness of the sample. All measurement of L, t and ω were made by using digital vernier. The exess of oxygen content (δ) could be determined by useing chemical method called Iodometric titration.The structure of the prepared sample was obtained by using x-ray diffractometer (XRD) type (Philips) which have the following features, the source Cukα current (20 mA), voltage (40 KV) and λ=1.5405 A 0. A computer program was established to calculate the lattice parameters a,b,c this program is based on Cohen,s least square method.The volume fraction of any phase (Vphase) in the sample were determined by using the relation(14): Vphase=      InII Ia ......21 x100 Where Ia is the XRD peak intensity of the phase which were determined,I1,I2,…In are the peaks intensity of all XRD. A computer program was established to calculate the lattice parameters a,b,c this program is based on Cohen , s least square method[8]. Results and Discussion The temperature dependence of the electrical resistivity(ρ) for Sb free sample and samples with different Sb contents (x=0.1 and x=0.15) in Hg0.5 Pb1-xSbxBa2Ca2Cu3O8+δ) are shown in figure (1). It is found from this figure that the behavior of resistivity with temperature of the composition which has no Sb is semiconductor while the addition of Sb content in the Hg0.5 Pb1-xSbxBa2Ca2Cu3O8+δ) transform from normal state at (x=0.1) to superconducting state at IBN AL- HAITHAM J. FOR PURE & APPL. SCI. VOL.24 (2) 2011 x=0.15(The value of critical transition temperature (Tc(off)) for as grown Hg0.5 Pb0.35Sb0.15Ba2Ca2Cu3O8+δ phases is 126K). This behavior is due to the fluctuation of oxygen excess and the increasing of Sb, while may lead to metastable structure, that decrease Tc, but most of them x=0.15, transform the structure to a stable phase. A small amount of Sb addition is quite effective in decomposing the low-Tc phase (1212) of Hg(Pb)Ba2Ca2Cu3O8+δ superconductor systems by producing BaHgO3 and BaCuO2 accompanied by high-Tc phase formation. The destruction of the low phase by Sb at the early stage may enhance the nucleation and the formation of high-Tc phase. Enhancement of free Sb will raise the resistivity and this will, much more, increase BaPbO3 which is an insulator consisting of Hg- O. The XRD data collected from various samples (samples having various Hg, Pb, Sb Ca, Ba and Cu concentration) were all polycrystalline and correspond to Hg(Pb,Sb))-1223 phases. The XRD also shows some impurity phases with vanishingly small concentrations. The representative XRD patterns are shown in figures(2 ). It could be seen from the spectra that there were three main phases in all samples of the Hg-base systems, high-Tc phase (1223) reflections (peaks H), and Low –Tc phase reflections (peaks L)and a small amount of impurity phases of (Ca, Ba)2CuO3, CaPbO4, CaSbO4 and CuO. The appearance of more than two phases could be related to the stacking faults along the c-axis. The comparison between the relative intensities of XRD patterns for the samples with Sb=0, 0.1 and 0.15, with the relative intensity of the same reflections of the sample with Sb=0 shows that all the samples have reflection intensity of the High-Tc phase reflections and Low –Tc phase reflections the H-peaks increased and Low-Tc decreased by increasing Sb . The High-Tc phase reflections of the free sample (Tl= 0) has lower intensity than samples have Sb . The lattice parameters have been estimated using d-values and (hkl) reflections of the observed x-ray diffraction pattern through the software program), the parameters a, b, c , Mass density ρM and volume fraction (Vphase) shown in table(1).Figures (3), (4), (5) and(6) show an increase of the volume fraction (Vphase) and decrease C, C/a and ρM for Hg-doped samples for different composition of Hg0.5 Pb0.5-xSbxBa2Ca2Cu3O8+δ as comparable with the free Sb sample. Conclusions We have synthesis of Hg0.5 Pb0.5-xSbxBa2Ca2Cu3O8+δ HTSC phases (x= 0, 0.10 and 0.15) have prepared solid state reaction method. It is found that the behavior of resistivity with temperature of the composition which has no Sb is semiconductor while the addition of Sb content in the Hg0.5 Pb1-xSbxBa2Ca2Cu3O8+δ transform from normal state (x=0.1) to superconducting state x=0.15(The value of critical transition temperature (Tc(off)) for as grown Hg0.5 Pb0.35Sb0.15Ba2Ca2Cu3O8+δ phases is 126K). The increasing of Sb leads an increase of the volume fraction (Vphase) and decrease c/a and ρM for samples for different composition of Hg0.5 Pb0.5-xSbxBa2Ca2Cu3O8+δ . References 1. Putilin ,S. N.; Antipov, E. V, O.; Chmaissem, M.and Marezio, (1993) ,Superconductivity at 94 K in HgBa2Cu04+ , Nature 362 ,226-228. 2. Schilling, A.;Cantoni M.;Guo J. D.and Ott, H. R. (1993) ,Superconductivity above 130 K in the Hg– Ba–Ca–Cu–O system, Nature 363, 56. 3. Chu, C. W.; Gao, L.; Chen, F.; Huang, Z. J.; Meng, R. L.and Xue, Y. Y. (1993) ,Superconductivity above 150 K in HgBa2Ca2Cu3O8+ at high pressures, Nature 365 ,323-225. 4. Jassim, K. A. (2009) Influence of simultaneous doping of T l on the transition temperature T c and the lattice parameters of HgBa2Ca2Cu3O8+ δ superconductors) Ibn Al-Haitham Journal for pure and applied sciences, , Baghdad university, college of Ibn Al-Haitham ,Baghdad,Iraq 22(3): 86-92. 5. Jassim, K.A. (2005) Comparison Study of T c Between the Superconducting Compounds Bi2- x(Hg,Pb)xSr2-y BayCa2Cu3O10+δ and Hg1-xPbxSr2-y BayCa2Cu3O8+δ , Ph.D Thesis , University of Baghdad , College of Science , Physics Dep. Iraq IBN AL- HAITHAM J. FOR PURE & APPL. SCI. VOL.24 (2) 2011 6. Rajiv Giri, G. D.; Verma, R. S.; T iwari and O. N. (2003) Srivastava (Influence of simultaneous doping of T l and Bi on microstructure and critical current density of HgBa2Ca2Cu3O8+d ) Cryst. Res. Technol. 38(9):760 – 766 7. Su J. H, Sastry P. V. P S S and Sch wart z, J. (2003) (Magnetization and transport properties of silver-sheathed (Hg, Re)Ba2Ca2Cu3O8+δ tapes) Supercond. Sci. Technol. 16 , 1134–1138 PII: S0953-2048(03)64411-8 8. Ferguson, I.F. and. Rogerson, A.H. (1984) , A program for the calculation of the intensities of x-ray or neutron powder reflections, part 3), Comput. Phys. Commun., .32, (Issue 1),. 83-94. Table(1): Values a,b,c ,c/a, δ and ρM for the samples for different composition of Hg0.5 Pb0.5-xSbxBa2Ca2Cu3O8+δ Fig. (1): Temperature dependence of resistivity for Hg0.5 Pb1-xSbxBa at indicated values of (Sb) at x =0.00, 0.10 and 0.15 X Tc(OFF)(K) Tc(ON) (K) δ(o2) a(A0) c(A0) c/a ρM (g/cm3) VPh-1223 0.00 ------ ------ 0.437 3.842 15 .99 4.161 5.9765 39.44 0.10 ------ ------- 0.353 3.844 15 .91 4.139 5.7351 55.17 0.15 126 135 0.233 3.843 15 .66 4.075 5.5841 75.79 IBN AL- HAITHAM J. FOR PURE & APPL. SCI. VOL.24 (2) 2011 Fig(2) XRD Patterns for the sample Hg0.5 Pb0.5-xSbxBa2Ca2Cu3O8+δ for x=0.00, 0.10 and 0.15 15.6 15.7 15.8 15.9 16 16.1 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 conce ntration Sb C ( A ) Fig.(3): parameter C as function of diferent Sb for Hg0.5 Pb0.5-xSbxBa2Ca2Cu3O8+δ IBN AL- HAITHAM J. FOR PURE & APPL. SCI. VOL.24 (2) 2011 30 40 50 60 70 80 0 0.02 0.04 0. 06 0. 08 0.1 0. 12 0.14 0.16 Concentrat ion Sb V o lu m e F ra c ti o n % Fig.(4): volume fraction (Vphase) as function of diferent Sb for Hg0.5 Pb0.5- xSbxBa2Ca2Cu3O8+δ 15. 6 15. 7 15. 8 15. 9 16 16. 1 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 concentration Sb C ( A ) Fig. ( 5): C/a as function of Sb concentration for Hg0.5 Pb0.5-xSbxBa2Ca2Cu3O8+δ 5.5 5.6 5.7 5.8 5.9 6 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 Concentra tion Sb M a s s D e n s it y ( g ra m /c m ) Fig. (6): Mass Density ρM as function of Sb concentration for Hg0.5 Pb0.5- xSbxBa2Ca2Cu3O8+δ