Effect of Y3+ substitution for Ca on the transport and mechanical properties of Bi2Sr2Ca1-xYxCu2O8+δ system

The influence of substitution of composition elements on the thermoelectric power (TEP) and microhardness (VHN) of Bi2Sr2Ca1-xYxCu2O8+delta, with 0.0 less than or equal to x less than or equal to 0.75, was investigated. Experiments studying the TEP or Seebeck coefficient (S) for the examined samples yielded, with increasing x, the carrier concentration decreases and the system changes from normal metallic state for x = 0.0 to insulating one for x = 0.75 through the superconducting phase. S of insulating sample (x = 0.75) is positive and large as in the case of similar samples of other Cu-oxides. The sample with x = 0.0 exhibited negative values for S in the entire measured temperature range. Meanwhile, for x = 0.55, the system tended to metal-insulator (M-I) transition. Superconductivity appears at x = 0.15, 0.25 and 0.35 and maximum transition temperature T-c(0) (98 K) for x = 0.35. This behaviour was attributed to the restoration of the weak-links of the electrical contact between grains. Also maximum value of density and microhardness occurs at x = 0.35, this trend was ascribed to the substitution of yttrium up to 0.35 can substantially suppress microcracking and improve the ductility of samples. From this study, it can be decided that the transport, superconducting and micromechanical properties are critically dependent on cationic non-stoichiometry and disorder. (C) 2003 Elsevier Science Ltd. All rights reserved.