Pb-doping effect on irreversibility fields of HgBa2Ca2Cu3O8+δ superconductors

Abstract

We prepared nearly single-phase polycrystalline samples of HgBa2Ca2Cu3O8+δ(Hg-1223) without and with Pb doping, i.e., Pb-free Hg-1223 and (Hg0.8Pb0.2)-1223, by means of a sample encapsulation technique. According to quantitative energy dispersive x-ray spectroscopy analyses and iodometric oxygen titration, the Pb-free Hg-1223 and the (Hg0.8Pb0.2)-1223 sample were identified to be Hg0.97Ba2.00Ca2.04Cu3.00O8.33 and (Hg0.79Pb0.29)Ba2.00Ca1.98Cu2.94O8.42, respectively. The highest Meissner-signal onset temperatures for the Pb-free Hg-1223 (after post-annealing in O2 gas) and the (Hg,Pb)-1223 (as-sintered) sample were observed at 135.4 and 132.0 K, respectively. The difference in the irreversibility fields (Hirr) for both samples was very small at temperatures above 80 K, while, at temperatures below 70 K, the Hirr versus T curve for the (Hg,Pb)-1223 sample shifted toward the higher field side. Thus, Pb doping was effective for the improvement of magnetic property of Hg-1223 superconductors, at least, at temperatures below 70 K.