The impact of Y substitution on the 110 K high Tc phase in a Bi (Pb):2223 superconductor

The structural and superconducting properties of Bi1.7Pb0.3Sr2Ca2-xYxCu3Oy superconducting samples are investigated by X-ray diffraction (XRD), resistivity and thermoelectric power (TEP) measurements. XRD results reveal that the volume percentage of the 2223 high T-c phase decreases with an increase in Y content. The replacement of the Ca2+ ion by the Y3+ ion does not influence the tetragonal structure of the pure Bi (Ph): 2223 system and the lattice parameters vary with Y content. The results of resistivity indicate that the critical temperatures Tc of the samples decrease monotonically with an increase in Y content. Further, the critical concentration of Y to completely suppress superconductivity in the Y-doped Bi (Pb):2223 system is higher (0.60) than that reported (0.20) for the other rare-earth elements. On the other hand, the values of TEP at room temperature are found to be negative for Y = 0.00 and 0.10 samples, and it changed to positive with further increase in Y content, The hole-carrier concentration per Cu ion (P) is deduced by using two different ways: the first in terms of T, values in the superconducting state and the other in terms of TEP values in the normal state. Interestingly, it is found that the values of P deduced from the formal way are not consistent with the reported parabolic behavior for superconducting systems in the under-doped region, and consequently disagree with the general roles of substitution. However, the vice versa is recorded for the values of P deduced from the latter way. The results are discussed in terms of the possible reasons for the suppression of superconductivity in the considered system. (C) 2008 Elsevier Ltd. All rights reserved.