Enhancement in superconducting transition temperature and J_c values in Na-doped Bi_2Sr_2Ca_1Cu_(2-x)Na_xO_y superconductors

摘要

The effects of Na substitution on the properties of Bi_2Sr_2Ca_1Cu_(2-x)Na_xO_y were investigated. The prepared samples are characterized using X-ray powder diffraction, scanning electron microscope, DC electrical resistivity and magnetic-hysteresis loop measurements. It has been found that with increasing Na doping for Cu, the transition temperature gradually increase while crystal lattice parameters slightly change. Magnetic hysteresis measurements have shown that the hysteresis loops of doped samples are greater than the undoped sample. In addition, significant enhancement has been observed in the J_c values of Na-doped samples, which were calculated from the M-H curves by using Bean's critical state model.