A Possible High Critical Temperature and Intergranular Current Density in Bi2Sr2CaY x Cu2 O y Superconductors

Abstract

We report here the structural and superconducting properties of Bi2Sr2CaYxCu2Oy superconductors with various x values (0.00 ≤x≤ 0.50) by using the resistivity and ac susceptibility measurements. It is found that addition of Y 3+ does not influence the phase purity of Bi:2212, while c-parameter and orthorhombic distortion are affected. Furthermore, the critical temperatures Tc(R= 0) are increased from 92 K for Y = 0 up to 106 K by 0.15 of Y, followed by a decrease with increasing Y up to 0.50. It is interesting to note the resistivity of the samples with Y = 0.075 and 0.15 reaching to true zero value only at low dc currents up to 2 mA. Interestingly, the onset temperature of diamagnetism obtained from susceptibility data remains nearly unchanged at 94 K up to Y = 0.30, flowed by a decrease to 86 K at Y = 0.50. The superconducting volume fraction and critical currents are improved by Y addition up to 0.15, followed by a decrease with increasing Y up to 0.50. These results are explained in terms of the effects of excess oxygen, secondary phases, and carrier concentration per Cu ions which are produced by Y addition in Bi:2212 system.