Effect of Pb addition on thermoelectric power and microhardness of Bi-Pb-Sr-Ca-Cu-O superconductors

The effect of (Pb) addition on the zero thermopower temperature (T-c(o)) and room temperature Vickers microhardness (VHN) of superconducting specimens of different nominal compositions based on the system Bi2-xPbxSr2Ca2Cu3Oy (x = 0.0, 0.1, 0.2, 0.3 and 0.5) were studied. Tilt addition of(0.3Pb) resulted in an increase in T-c(o) from 93 to 113 K and a 2.85-fuld increase in the microhardness for considered loads. This behaviour is ascribed to the presence of large amount of the high-ir, phase (2223). Furthermore, fb particles may relax the residual stresses resulting from the expansion of individual grains, and may provide increased resistance to crack propagation by pinning the propagating cracks; these effects would increase the hardness. The addition of (0.5Pb) resulted in a decrease in T-c(o) to 98 K, and also VHN decreases almost 2.44 times. This decrease in T-c(o) and VHN is believed to he due to the formation of contaminating phases such as Ca2PbO4. Indexed X-ray diffraction patterns indicated that high abundancy of the 2223 phase for the specimen (0.3Pb) are characterized by the sharpest superconducting transitions. Also the present study proved that the most convenient Pb content to obtain a minimum value of porosity is equal (0.3Pb), (C) 2000 Elsevier Science Ltd. All rights reserved.