Role of rare-earth Ba2+ doping in governing the superconducting and mechanical characteristics of Bi–Sr–Ca–Cu–O

The effect of barium doping on the superconducting and mechanical properties in the Bi2Sr2Ca2BaxCu5Oy (BSCCO) system has been investigated by thermoelectric power (TEP), Vickers microhardness (VHN), x-ray diffraction (XRD), and scanning electron microscope (SEM) analysis. Barium was incorporated with x ranging from 0.0 to 0.82. The temperature variation of the thermopower (Seebeck coefficient) S shows that the critical transition temperature Tc0 is enhanced (to 93 K) up to x = 0.45 and then disappears for x = 0.82. The results have also suggested an increased interaction of electrons and holes with phonons at low temperatures. The enhancement of Tc0 is ascribed to the improvement in electric connection between superconducting grains. XRD data show that the high-Tc (2:2:2:3) phase increases and the low-Tc (2:2:1:2) phase decreases as the barium concentration changes from x = 0.0 to 0.45. SEM analysis of a sample (x = 0.45) shows that plate-like grains (2223 phase) are formed. Also, an appropriate level of Ba dopant improves the microhardness and fracture toughness remarkably. The optimum dopant level of Ba from the point of view of mechanical properties is x = 0.45. The improvement of mechanical characteristics is due to the fact that Ba2+ can fill the intergrain spaces, and thereby reinforce the coupling between granules. From the above results, it is inferred that the added Ba has the positive effect of decomposing the structure of the low-Tc phase, leading to the production of BaBiO3 and BaCuO2 and enhancing the high-Tc phase creation.