Annealing temperature effect on the properties of Bi:2212 superconducting system

We report here the effect of annealing temperature (750-850 °C), when annealing in air for 50 h, on the structural, mechanical and superconducting properties of Bi2Sr2CaCu2O8+δ (Bi:2212) system. X-ray diffraction, bulk density and microhardness measurements for sintered and annealed Bi:2212 are presented in details. The superconducting critical temperature Tc, the residual resistivity ρo and the resistivity slope corresponding to the linear ρ-T region are extracted from electrical resistivity measurements. It is found that the amount of low-Tc phase (2212) is gradually increasing with increasing annealing temperature up to 850 °C. Interestingly, the critical temperature Tc is found to be increased from 78 up to 100 K by increasing the annealing temperature, along with sharpening of the transition. The sharpest transition may be attributed to a high homogeneity of the superconducting grains. Moreover, the Vickers microhardness (VHN) and the bulk density are also increased with annealing temperature increase. This behavior reflects the improvement of the coupling between superconducting grains. From these observations, one can see clearly that the improvement of electrical resistivity and micro-hardness is caused by elimination, by annealing, of oxygen disorder and microcracks elimination.