Effect of Ni and Zn Substitutions for Cu in the 25 K Phase of Bi–Sr–La–Cu–O Superconductors

Abstract

We investigate the effect of Ni and Zn substitutions for Cu on the lattice parameters, phonon vibrational feature, electronic structure, as well as transport properties in Bi2Sr1.8La0.2CuOy . The experimental data show that both Ni and Zn are soluble in the Bi2Sr1.8La0.2CuOy material up to about 10% of the Cu content. In Bi2Sr1.8La0.2Cu1-x Nix Oy system, the superconducting critical temperature T c decreases linearly with Ni concentration and the rate of T c decrease is around 2.5 K/at.%, while for Bi2Sr1.8La0.2Cu1-x Znx Oy system the dependence of T c on the Zn dopant concentration deviates from a linear behavior and the Zn substitution suppresses the T c much stronger than the Ni substitution. The comparison of the phonon vibrational feature of the apical oxygen atoms in the CuO6 octahedron between the Bi2Sr1.8La0.2Cu1-x Nix Oy and Bi2Sr1.8La0.2Cu1-x Znx Oy systems shows that the Zn substitution leads to a more serious structure distortion than the Ni substitution. In addition, the electronic structures of the two doped systems were compared using XPS spectrum. The results show that the Zn substitution reduces Cu oxidation level more remarkably than the Ni substitution. Some possible explanations for the stronger suppression of T c by the Zn substitution than by the Ni substitution are provided, based on these experimental results.