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)) an d 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) resu lted 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 p resence of large amount of the high-ir, phase (2223). Furthermore, fb parti cles may relax the residual stresses resulting from the expansion of indivi dual grains, and may provide increased resistance to crack propagation by p inning the propagating cracks; these effects would increase the hardness. T he addition of (0.5Pb) resulted in a decrease in T-c(o) to 98 K, and also V HN 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. Indexe d X-ray diffraction patterns indicated that high abundancy of the 2223 phas e for the specimen (0.3Pb) are characterized by the sharpest superconductin g transitions. Also the present study proved that the most convenient Pb co ntent to obtain a minimum value of porosity is equal (0.3Pb), (C) 2000 Else vier Science Ltd. All rights reserved.