Improvement of magnetic properties in Bi-2212 ceramics by fluorine doping

Superconducting ceramics of Bi2Sr2CaCu2OyFx with x=0, 0.2 and 0.4 are prepared by conventional solid state reaction. They are characterized by means of XRD, SEM, EDX and magnetic measurements. Unlike the low temperature fluorination method described by other authors, the study shows that the superconducting volume fraction of samples increases gradually with fluorine doping. The critical transition temperature is observed to be constant in all samples suggesting that fluorine substitution do not affect the CuO2 planes. Hysteresis loops measured at 5 and 50 K indicate an improvement of the irreversible magnetization of the samples as fluorine content is increased. The deduced critical current density follows the same variation. At 50 K and 1 kG, this current vanishes in the undoped sample while it persist in the doped ones.