The effect of (Pb) addition on the zero thermopower temperature
To
c and room temperature Vickers microhardness (VHN)
of superconducting specimens of different nominal compositions based on the system Bi22xPbxSr2Ca2Cu3Oy
x 0:0; 0.1, 0.2,
0.3 and 0.5) were studied. The addition of (0.3Pb) resulted in an increase in To
c from 93 to 113 K and a 2.85-fold increase in the
microhardness for considered loads. This behaviour is ascribed to the presence of large amount of the high-Tc phase (2223).
Furthermore, Pb 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 To
c to 98 K, and also VHN decreases almost 2.44 times. This decrease in To
c and
VHN is believed to be 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). q 2000 Elsevier Science Ltd. All rights reserved.