Chemical Stabilization and Flux Pinning in Hg-Based Superconductors

Abstract

Effect of chemical stabilization by substitution of a small amount (0.1~0.25) of rhenium (Re) ion on the Hg-site in HgM₂Ca_n-1Cu_n0_y (M=Ba or Sr, n=l~4) has been studied. The flux pinning behavior in these Hg-based compounds has been enhanced substantially compared to the undoped parent materials. By a neutron diffraction analysis on the Hg(Re)SrCaCuO (n=2,3) compounds, Re was found to occupy the Hg-site with octahedrally fully coordinated oxygen ions, giving rise to the stabilization of Hg(Re)0 plane and shortening of the blocking layer thickness. At the same time, the Re ion whose binary oxide ReOß is extremely conductive, is considered to contribute to the better electrical conduction along the c-axis direction. These factors should be quite effective in increasing the interlayer superconducting coupling strength via the decrease in the electromagnetic anisotropy. Observation by HRTEM has also suggested a possibility of microscopic segregation of Re ions in the HgO plane, which might act as effective pinning centers of the flux lines in the mixed state.