SYNTHESIS OF OXYCARBONATE SOLID-SOLUTIONS (TL1-XHGX)SR2BA2CU2(CO3)O-Y(X=0-1.0) AND SUPERCONDUCTIVITY

Solid solution superconductors (Tl-1-x Hg-x)Sr2Ba2Cu2(CO3)O-y were syn thesized for x= 0-1.0. The crystal structures, especially its superstr ucture and superconducting properties, were examined by X-ray powder d iffraction, electron microscopy, resistivity and susceptibility measur ements. The three different crystallographic phases have been observed ; Phases I and II have an 8 times commensurate and 7.5 times incommens urate crystal structure and their propagation vector is along [010]. P hase 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 o xygen deficiency with increasing Hg content. T-c also suddenly dropped from 70 to 60 K at about x=0.7-0.8.