High resolution electron microscopy study of the high Tc superconductor Tl0.5Pb0.5Sr4Cu2CO3O7

The structure and the microstructure of the new high Tc superconductor Tl0.5Pb0.5Sr4Cu2CO3O7 have been studied by high resolution electron microscopy. The experimental images fit well with the calculated ones based on a structure built up from the intergrowth of a 1201-type slice [Tl0.5 Pb0.5 Sr2Cu Co5[1201∞ with a [Sr2Cu Co3O2[∞unit. The comparison of the calculated and experimental images with those of a 1223 structure, which exhibits similar cell parameters to those of Tl0.5Pb0.5 Sr4Cu2CO3O7, shows that the oxycarbonate exhibits a characteristic contrast for some focus values which allows to differentiate the two structures. The investigation of numerous crystals attests of the high regularity of the stacking of the layers along c. One single type of defect was observed which suggests the possible existence of a new member [Tl0.5Pb0.5 Sr2CuO5[[Sr2CuCO3O2[2. (author). 13 refs., 10 figs., 1 tab