Enhancement of superconducting properties of Bi-2212 ceramics by vanadium-sodium co-doping

Bi2Sr2-xVxCa1Cu1.75Na0.25Oy superconductors with x = 0, 0.05, 0.1 and 0.25 were prepared by the classic solid-state reaction method. The effects of vanadium substitution have been investigated by means of X-ray powder diffraction, scanning electron microscopy, dc electrical resistivity, and magnetic hysteresis loop measurements. Results show that the superconducting properties of Bi-2212 phase can be significantly improved with x = 0.05 vanadium substitution. SEM micrographs show the presence of plate-like crystals in all samples, implying the composition of 2212 phases. In addition, J(c) values of the samples were calculated from the hysteresis loop measurement by using the Bean's model showing that J(c) significantly increases with x = 0.05 vanadium substitution.