DISTRIBUTION OF SUBSTITUTION CLUSTERS, CHANGE OF POSITRON LIFETIME AND SUPERCONDUCTIVITY IN MAGNETIC ION Fe AND Ni DOPING YBa2Cu3O7-δ SYSTEMS

Abstract

To recognize the distributional characteristics of Fe and Ni doping and the fundamental effects of magnetic ions on superconductivity, the X-ray diffraction, positron annihilation technology and simulated calculations are utilized to investigate systemically YBa 2 Cu 3-x( Fe , Ni )x O 7-δ(x=0.0~0.5). The results show that Fe and Ni doping form different kinds of ion clusters and enter the crystal lattice. When occupying Cu (2) sites in the CuO 2 planes, ions gather into Double Square and/or other clusters, which results in a strong electronic localization and would directly influence the pairing and transportation of carriers, so the superconductivity is suppressed dramatically. While doping ions enter the Cu (1) sites through gathering Hexamer and/or other clusters, this induces the localization of holes and weakens the function of carrier reservoir, so carriers cannot be easily transferred to the CuO 2 planes. However, in this case, the pairing and transportation of carriers are not affected directly, thus the superconductivity is suppressed weakly. Besides, the present results indicate that the superconductivity suppressed has no direct correlation with the magnetism of Fe and Ni ion itself.