Synthesis of oxycarbonate solid solutions (Tl_1-xHg_x)Sr₂Ba₂Cu₂(CO₃) (x=0-1.0) and superconductivity

Solid solution superconductors (Tl_1-xHg_x)Sr₂Ba₂Cu₂(CO₃)O_y were synthetized for x=0-1.0. The crystal structures, especially its superstructure and superconducting properties, were examined by X-ray powder diffraction, electron microscopy, resistivity and susceptibility measurements. The three different crystallographic phases have been observed; Phases I and II have an 8 times commensurate and 7.5 times incommensurate crystal structure and their propagation vector is along [010]. Phase III has a 4.7-4.5 times incommensurate structure along the [110] direction. The discontinuous change at about x=0.7-0.8 is due to the oxygen deficiency with increasing Hg content T_c also suddenly dropped from 70 to 60 K at about x=0.7-0.8.