Optimal and overdoped superconducting regimes in Hg-2212 system by Pb substitution

Abstract

Lead substitutions on Hg site and Ca substitutions on Y site have been studied in the Hg-2212 compound in order to reach its optimal doping composition. The unit cell evolution has been studied by powder X-ray diffraction and the structure refined from X-ray synchrotron powder diffraction data. The Pb4+ substitution stabilizes the Hg2O2-δ layer allowing full Ca substitution on the Y site. The Ca doping makes the Ba-O2 plane to move away from the Hg-O3 plane, it also reduces the buckling which remains still high (9.7°). The superconducting transitions correspond to optimally and overdoped samples. The Tcmax (82-84 K) is found identical as in (Hg,Tl)-2212 samples suggesting this value to be intrinsic at optimal doping. © 2002 Elsevier Science B.V. All rights reserved.