GLUCOSE DOPING IN l MgB_2 SUPERCONDUCTORS:PINNING MECHANISM

In this paper,the critical current density Jc of pure and glucose-doped MgB2 bulk samples have been obtained by magnetic measurement.The effects of doping on the flux pinning mechanism have been analyzed according to the collective pinning model.It is found that the δTc pinning mechanism is mainly responsible for pure MgB2 sample while the δl pinning mechanism becomes dominant for glucose-doped samples.Further investigation revealed that in doping samples the δTc pinning also appeared,but with the increasing doping level the proportion of δTc pinning decreased,while the δl pinning gradually increased to 90%.The corrected residual resistivity results confirm the change of pinning mechanism in doped samples.It is demonstrated that the δl pinning is mainly caused by the lattice disorder effect arising from the substitution effects of carbon.