Effects of MgO, MgB₂ and YBCO addition on formation, microstructure and superconducting properties of Bi₁.₆Pb₀.₄Sr₂Ca₂Cu₃Oδ ceramic

The superconducting properties of Bi1.6(Pb0.4)Sr2Ca2Cu3Oδ(M)(BPSCCO) added with M=MgO, MgB2 and YBCO have been studied so as to acquire further information related to the effect of superconducting and non-superconducting impurities as pinning centers in the bulks BPSCCO. Samples of (Bi1.6(Pb0.4)Sr2Ca2Cu3Oδ)1-x(M)x at x=0.00-0.10 were prepared using solid state reaction method. The samples were calcinations for 3 times at 800oC for 20 hour, 820oC for 10 hours and 840oC for 4 hours then sintered in air at 855oC for 96 hours followed by annealing at 830oC for 30 hours. The transport properties of the samples were measured using x-ray diffraction (XRD), Scanning electron microscope (SEM), Energy Dispersive X-ray (EDX), four-point probe electrical resistance measurement and magnetic properties were measured by using Alternating Current Susceptibility (ACS). X-ray diffraction (XRD) technique showed that all samples are in polycrystalline phase with some of the peaks belonging to Bi-2223 and Bi-2212 as determined from Reitveld Refinement Technique. The structural properties such as volume fraction and lattice parameter were calculated using volume percentage equation and Bragg’s Law. The XRD peaks increased when x=0.02 (MgO, MgB2 and YBCO) for all samples and dominated by Bi-2223 (about 76%). However, the volume fraction of Bi-2223 phase decreased gradually as the addition of materials increased. The sample was still dominated by Bi-2223 phase with slight increase in Bi-2212 phase. The lattice parameters calculated from XRD data show a slight decrease in the c-axis while a-axis and b-axis increases. The decrease at the lattice of c-axis may be due to the increase in oxygen content. The reason that a-axis and b-axis increases may be due to extra electrons valence on Cu so that these is an increase of Cu-O bond length. Scanning Electron Microscope (SEM) images showed the flaky plate-like grain structure samples, in which the grains size become smaller with higher addition concentration. The elemental analysis by EDX measurement of samples reveals the existence of additives materials that are distributed in Bi-2223 matrix. The resistivity measurement showed that all samples exhibit normal metallic behavior in the normal state. Critical temperature TC(R=0) which is around 98 K for pure sample while it was found gradually to increase to higher temperature with x=0.02 (100 K, 99 K and 102 K), the TC(R=0) decreases gradually to lower temperature. The holes concentration of pure sample is around 0.127 and this value decreases as the addition concentration increase. The behavior of weak link and intergranular coupling was studied using Alternating Current Susceptibility (ACS) technique. Diamagnetism onset temperature TC-ON was observed from real part (χ’), where a two-step transition is related to the superconducting intra and intergrain coupling. The intra and intergranular AC loss peaks as observed from imaginary part, (χ’’) move to lower temperature and the height and the width of the peaks increase showing the extend of the AC loss. Analysis of the temperature dependence of the ACS near the transition loss peak temperature Tp has been done by using Beans’s Critical State Model. The higher percentage of additives increase the behavior of weak link and intergranular coupling. It was found that the Bi-2212 phase and additions of additives on the grain boundaries play the role in influencing the intergranular coupling and weak links. The calculated value of Josephson current, Io obtained from the AC susceptibility data showed a much higher value Io=123.21 μA for addition with YBCO (x=0.02) as compared to the pure samples with Io=119.83 μA. The diamagnetic behaviour is decreased and shifted toward the lower temperature due to the improvement of weak link connectivity.

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