Fluorine Doping Effect in the New Superconducting Y₃Ba₅Cu₈O_y Compound

Abstract

The newly identified yttrium based high critical temperature (Tc) superconductor of composition Y 3 Ba 5 Cu 8 O y (Y358) and the fluorine doped Y 3 Ba 5 Cu 8 O y-0.2 F 0.2 (Y358+F) compounds were synthesized by solid state reaction technique. The micro structural and morphological features of the synthesized samples were investigated by X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM) and Energy Dispersive Spectrum (EDS) analysis. The XRD of the samples revealed a structure similar to Y 1 Ba 2 Cu 3 O y-o (Y123) compound with about three fold larger ‘c’ axis. The SEM image of the fluorine doped sample (Y358+F) showed a needle like inter growth which was different from that of pure (Y358) sample. The Tc of the sample, measured by self inductance method showed an onset of superconductivity at 92 K for the pure and 98 K for the fluorine doped sample. On further heating the fluorinated sample for 24 hours, the needle like intergrowth had disappeared as seen from SEM micrograph and the Tc onset of the sample had increased to 110 K with a two step transition.