Structural and transport properties of Nd doped (Bi,Pb)-2212

Abstract

We report here the effect of Nd substitution (at Sr site) on the crystallographic, normal, and superconducting state properties of the high temperature superconductor Bi 1.7Pb 0.4Sr 2− x Nd x Ca 1.1Cu 2.1O y (0.0 ⩽ x ⩽ 0.5). The structural and compositional analysis [X-ray diffraction analysis (XRD) and energy dispersive X-ray analysis (EDX), respectively] reveals that Nd ions enter into the Sr site of (Bi,Pb)-2212 crystal structure and scanning electron microscopy (SEM) results show a morphological change for higher concentration of Nd. The low temperature thermal and electrical transport measurements, electrical resistivity ( ρ), thermoelectric power (TEP) and thermal conductivity ( κ) show significant variations in critical temperature ( T C) as well as normal state properties upon Nd substitution. The sign reversal and the palpable variation in the magnitude of TEP as a function of Nd composition shows that Nd substitution at Sr site decreases the hole concentration. As the Nd concentration increases, the magnitude of ρ increases whereas κ decreases, which is in good agreement with the reduced electronic contribution towards the total thermal conductivity. The critical current density is found to be much higher for the optimum level of Nd substitution than those of pristine sample. These changes in the thermal and electrical transport properties are attributed to the decrease in the hole concentration in the Cu–O planes, which changes the system from ‘over-doped’ to ‘optimal-doped’ and then to ‘under-doped’ condition.