The influence of oxygen content on the Tc of HTS Hg-1245

Анотація

We have observed an extraordinary behavior of the HgBa₂Ca₄Cu₅O_12+d layered HTS (phase 1245) in the overdoped state. Earlier we have synthesized the phase Hg-1245 with different oxygen content and consequently different values of the lattice parameter a. We have observed a coincidence of a values when the T_c(a) cupolas reach their maxima for phases Hg-1223, 1234, and 1245, and a merging of their overdoped parts together with abrupt falling off of the T_c values. The Hg-1245 phase has shown the most unusual behavior. Contrary to other phases, this one contains three types of CuO₂ layers in a unit cell. We supposed that, in the case of the Hg-1245 phase, the holes coming from the reservoir, which is the Hg-O plane, cannot reach the &quotfar&quot CuO₂ layer which is notable for this phase. We have calculated the hole concentration for each layer for 1223, 1234, and 1245 phases. The results obtained confirm our assumption. The hole concentration appears negligibly small for the overdoped 1245 phase. We can consider the &quotfar&quot CuO₂ layer as not taking part in superconductivity. The analysis of the behavior of the T_c(a) cupolas for the phases with different number of CuO₂ layers and of hole density distribution between the layers has been carried out.