Effects of Al_2O_3 nanometer particles addition on the fluctuation conductivity in (Bi,Pb)-2223 superconductors

摘要

Nanometer Al_2O_3 particles were added to (Bi,Pb)_2Sr2Ca_2Cu_3O_x (Bi,Pb)-2223 precursor powders during the final sintering cycle of a multi-step preparation process. The temperature dependence of the resistance in 0 and 0.2% Al_2O_3-added (Bi,Pb)_2Sr_2Ca_2Cu_3O_x samples was measured. Data about the dimensionality of the fluctuation is obtained by analyzing the fluctuation conductivity Δσ as a function of ε-ln(T/T_C) on the basis of the Aslamazov-Larkin theory. Within the mean field region, we first observe a regime dominated by 2D Gaussian fluctuation. With decreasing temperature a crossover occurs at a temperature T_G and the obtained regime was described by critical fluctuations. The Ginzburg number and fluctuation amplitude, increase with addition of nanometer Al_2O_3 particles. Correlation between fluctuation amplitude and J_C has been discussed.