Tc, onset, fluctuation and intergrain connection in the Bi_2−xGe_xSr₂CaCu₂O_8+δ

Abstract

Resistive transitions in Bi_2−xGe_xSr₂CaCu₂O_8+δ(x=0-0.3) prepared by the solid state reaction method were investigated. The T_c,onset’s of the as sintered pellets were approximately 74 K and 80 K for x=0 and x>0 respectively. To enhance intergrain connection, the sintered pellets were subsequently cold pressed then annealed. This increases the T_c,onset to approximately 87 K for all x and sharpens the resistive transition. Although the intergrain connection enhanced samples have almost the same T_c,onset independent of x, the superconducting fluctuation for x>0 starts at a much higher temperature compared to that of x=0. An analysis following the Aslamasov-L arkin theory suggests different behaviors in fluctuation dimensionalities between the Bi:Ge substituted and unsubstituted samples.