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

Abstract

Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Sr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2-x</sub> Yb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> CaCu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sub> +O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8+δ</sub> (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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) and critical current density (J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) 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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> . Significant improvement of 25% in the critical current density (J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) has been achieved with an Yb doping content of 0.01.