Abstract:The effect of the partial substitution of Ca 2+ by Ho 3+ ions on the electrical and mechanical properties of the superconducting phase (Bi,Pb)-2223 was studied. Superconducting samples of the type (Bi 1.8 Pb 0.4 )Sr 2 Ca 2.1−x Ho x Cu 3.1 O 10+δ were prepared by solid-state reaction technique under ambient pressure, and characterized by means of X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The superconducting transition temperature T c and pseudogap temperature T * were estimated from electrical resistivity measurements, while the critical current density J c was determined from I-V curves. The electrical resistivity data were discussed according to bipolaron model in the absence of thermally excited individual polarons. The sample with x = 0.025 showed the highest phase volume fraction, T c , and J c . Room temperature Vickers microhardness measurements were carried out at different applied loads (0.25-5 N) in order to investigate the performance of the mechanical properties of (Bi 1.8 Pb 0.4 )Sr 2 Ca 2.1−x Ho x Cu 3.1 O 10+δ phase. It was found that all the samples exhibit normal indentation size effect (ISE). The Vickers microhardness number H V increased as x increased from 0 to 0.025. The experimental results were discussed in view of Meyer's law, Hays-Kendall (HK) approach, elastic/plastic deformation (EPD) model, and proportional specimen resistance (PSR) model. The load independent (true) microhardness of (Bi 1.8 Pb 0.4 )Sr 2 Ca 2.1−x Ho x Cu 3.1 O 10+δ superconducting samples showed identical behavior to that of the PSR model.

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This investigation reports the effect of the addition of CdO nanoparticles on the (Bi,Pb)-2212 superconducting phase. The superconducting samples of general formula (CdO)x Bi1.6 Pb0.4 Sr1.9 Ca1.1Cu2.1 O8 (x = 0.00, 0.01, 0.02, 0.05, and 0.1 wt%) are synthesized using the conventional solid-state reaction technique. Powder X ray diffraction analysis confirms the formation of a single-phase orthorhombic Bi-2212. The variations in the lattice parameters are explained based on the Jahn Teller distortion induced by the increase in the oxygen content owing to the addition of the CdO nanoparticles. The increase in the oxygen content is confirmed via Idiometric titration analysis. The grain morphology is investigated using scanning electron microscopy (SEM). The effect of CdO addition in enhancing grains connectivity by the filing of pores and voids is revealed. Fourier transform infrared (FTIR) spectroscopy is conducted to analyze the functional groups, based on the effect of calcination temperature and CdO addition. Dc-electrical resistivity measurements and I-V characteristics show an enhancement of the superconducting transition temperature (Tc) and the critical current density (Jc) with CdO addition up to x=0.05 wt%, followed by a further decrease. By analyzing the results of the X-ray photoelectron spectroscopy (XPS), the variations of the superconducting properties are explained based on the preferred substitution of Pb2+ ions in the Bi3+ or Cu2+ sites induced by the variations in the oxygen content generated by the addition of CdO nanoparticles.

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