Electrical and mechanical properties of (Bi,Pb)-2223 substituted by holmium

The effect of the partial substitution of Ca2+ by Ho3+ ions on the electrical and mechanical properties of the superconducting phase (Bi, Pb)-2223 was studied. Superconducting samples of the type (Bi1.8Pb0.4) Sr2Ca2.1-xHoxCu3.1O10+delta 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 (Bi1.8Pb0.4)Sr2Ca2.1-xHoxCu3.1O10+delta 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 (Bi1.8Pb0.4) Sr2Ca2.1-xHoxCu3.1O10+delta superconducting samples showed identical behavior to that of the PSR model.