SYNTHESIS AND CHARACTERIZATION OF BI2SR2CACU2O8 WITHOUT EXCESS OXYGEN

The synthesis of superconductive Bi2Sr2CaCu2O8 without excess oxygen under an argon flow has been realized. A TGA method has been settled to determine the oxygen content of this phase with accuracy. The magnetic susceptibility and resistivity measurements performed on this pure phase have shown that it is a bulk superconductor with a T(c(onset)) of 86 K. The influence of the thermal treatment upon the superconductivity volume of different ceramics has been studied and explained in terms of microstructure and especially grain size variation. Grain boundary effects have been evidenced. The E.D. observations have shown that this oxide exhibits always a modulated structure with a q vector of 4.91 confirming the important role of Bi(III) 6s2 lone pair in the modulation. Superconductivity is also discussed as the result of the role of hole reservoir played by the [BiO] infinity layers according to the equilibrium Bi(III) + Cu(III) --> Bi(III-epsilon) + Cu(II+epsilon).