Impact of Bi2O3 addition on the normal state properties of Bi3.4Pb0.3Sr2Ca1.3−x RExCu2Oy ceramics

The impact of Bi₂O₃ addition on the structural, microhardness (Vickers microhardness (VHN)), resistivity and Hall coefficient measurements of Bi_3.4Pb_0.3Sr₂Ca_1.3−x RE_xCu₂O_y ceramic samples with various x and RE is investigated. X-ray diffraction results indicate that all the peaks belong to Bi: 2212 and 2201 phases. The moderate amount of 2212 phase exists as a major phase, while the 2201 phase as a minor. The net intensity of all peaks I_max for 2212 phase increases with Y as compared to undoped sample, followed by a gradual decrease with further increase in rare earth (RE) up to La. While the vice versa is recorded for both 2201 phase and VHN. Except Y sample, a good link between flake-type grains is observed in the SEM photographs of the considered samples. The electrical resistivity turns from quiet metallic for undoped sample to semiconducting behavior for all substituted samples without any transition to the superconducting state. The Hall coefficient sign is found to be positive for undoped and Y samples and it changed from positive to negative for the other RE-substituted samples. The possible reasons for superconductivity quenching by RE substitution in this type of ceramic materials are reported.