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 Hg(0.55)Pb(0.25)T1(0.2)Ba(2)Ca(2)Cu(3)O(gamma) sup erconducting grain. The formation of these regions can be explained by a simple model which takes into account the growth of grains during t he Hg superconducting phase formation process. These surplus and defic ient regions result in a reduction of Hg superconducting phase and hen ce 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.