Influences of Yb Doping on the Structure and Superconducting Properties of Bi-2212 Single Crystals

Bi₂Sr_2-xYb_xCaCu₂O₈+O_8+δ (x = 0.00, 0.05, 0.10, and 0.20) single crystals with Yb substitution at the Sr sites are successfully obtained by the self-flux method. The single crystal with doping content x = 0.01 exhibits the highest critical temperature (T_c) and critical current density (J_c) values. The influences of Yb doping on the type, size, and density of the introduced defects have been investigated by high-resolution transmission electron microscopy. It displays that Yb doping can make the Bi-2212 crystal shrink. X-ray photoelectron spectroscopy is used to investigate the influence of doping content on the binding energies of certain elements, including O, Sr, and Cu, corresponding to the change of T_c. Significant improvement of 25% in the critical current density (J_c) has been achieved with an Yb doping content of 0.01.