EXTRA OXYGEN DEFECT INDUCED BY Fe-DOPING IN Tl-SYSTEM SUPERCONDUCTOR

In Fe-doped Tl-1223 superconducting phase, Fe-dopants significantly destroy superconductivity . Hall coefficient, thermogravimetric measurements and M?ssbauer effect show that Fe-dopants not only directly destroy the integrity of Cu-O layers to low superconduction transition temperature, but also induce extra oxygen to enter lattice. These extra oxygen defects can strengtheningly bind carriers in Cu-O layers, Such binding effect gives rise to decreasing of the carrier density with Fe-doping level increasing. In addition. the extra oxygen results in a deviation of its neibouring Fe(Cu) from center of Cu-O network, and from a new Fe-O coordination. It is important for high-Tc superconducting mechanism to study the structural details and carrier-binding effect of extra oxygen defect on superconducticity.