THE SYNTHESIS AND CHARACTERIZATION OF HGBA2CA2CU3O8+DELTA SUPERCONDUCTORS WITH SUBSTITUTION OF HG BY PB

We have successfully fabricated ceramic superconductors of Hg-1223 wit h substitution of Pb for Hg, i.e. Hg1-xPbxBa2Ca2Cu3Oy, by using encaps ulation and short time annealing techniques. Samples fabricated in thi s manner may have nearly single phase structure and some enhancement o f T-c can be achieved through this method. The materials of this ceram ic with x ranging from 0 to 0.5 exhibit high-temperature superconducti vity at temperatures falling in the range from 103 to 135 K. The sampl e with optimum doping of Pb of x = 0.34 and delta = 0.40 has a highest T-c of 135 K, and its diamagnetic onset temperature T-c(dia) = 143 K. The composition of this sample has been found experimentally and is s pecified by a formula of Hg0.66Pb0.34Ba2Ca1.98Cu2.97O8.4. The valence number for the copper constituent is given by ($) over bar V-Cu = 2.30 . X-ray diffraction (XRD), transmission electron microscope (TEM) and electron probe microanalyzer (EPMA) analyses have been carried out for detailed investigation. Results indicate that the critical temperatur e for samples which were post-annealed with either oxygen flow or in h igh pressure of oxygen gas was increased, while that for those anneale d in argon flow was decreased. Furthermore, the as-prepared samples we re slightly in the under-doped state with respect to the vacancy. It w as shown that T-c parabolically depends on the valence state of copper .