Effect of Metal Substitution in BSCCO Ceramic Superconductors

The fabrication, electrical, and optical properties of ceramic Bi_2-xM_xSr₂Ca₂Cu₃O_y (where M=Al or Ni and x=0.3) superconductors are described. Resistivity measurements reveal that when Al is partially substituted at the bismuth site in the BiSrCaCuO compound, T _c decreases to 77 K and the nickel-substituted compound shows a T _c of 70 K, compared to the undoped ceramic BiSrCaCuO samples with T _c of 85 K. Infrared reflectance measurements, which cover the 50-4000 cm^–1 range, find that the reflectance from the ceramic samples decreases in the metal-doped samples. The observed phonon modes in the infrared conductivity spectra (obtained by Kramers-Kronig analysis) decrease in strength and some features are completely smeared out. Furthermore some of the modes are observed to shift slightly in the frequency on doping, the change in the T _c and vibrational modes is attributed to destabilization of 2223 phase.