Distributions of the Hg, Pb and Tl atoms in a single grain of a Hg0.55Pb0.25Tl0.2Ba2Ca2Cu3Oy superconductor

Surplus and deficient regions of Hg, Pb and Tl atoms are found at some edges of a typical Hg0.55Pb0.25Tl0.2Ba2Ca2Cu3Oy superconducting grain. The formation of these regions can be explained by a simple model which takes into account the growth of grains during the Hg superconducting phase formation process. These surplus and deficient regions result in a reduction of Hg superconducting phase and hence increase the amount of weak links among the superconducting grains. This leads to a decrease of critical temperature compared to that of the Hg samples which are only substituted with either Pb or Tl.